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Virgin Islands perspective : V.I.P. : agricultural research notes. Vol. 2. Num. 1.
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Permanent Link: http://ufdc.ufl.edu/CA01300010/00001
 Material Information
Title: Virgin Islands perspective : V.I.P. : agricultural research notes. Vol. 2. Num. 1.
Series Title: Virgin Islands perspective : V.I.P. : agricultural research notes
Physical Description: Serial
Language: English
Creator: University of the Virigin Islands, Agricultural Experiment Station
Publisher: Agricultural Experiment Station, University of the Virigin Islands,
Publication Date: 1987
Genre: serial   ( sobekcm )
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Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 51690614
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Table of Contents
    Front Cover
        Front Cover 1
        Front Cover 2
    From the director
        Page 1
    Growth and reproductive characteristics in a flock of V.I. white (St. Croix) hair sheep
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
    Naturally-occurring legumes in the pastures of St. Croix
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
    Ciguatera fish poisoning in the Eastern Caribbean
        Page 12
        Page 13
        Page 14
        Page 15
    Yield results of vegetable varietal evaluation trials in the U.S. Virgin Islands
        Page 16
        Page 17
        Page 18
    Integrating fish culture and vegetable hydroponics: Problems and prospects
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
    Back Matter
        Page 24
    Back Cover
        Back Cover 1
        Back Cover 2
Full Text


f J


Plans perspective Agricultural Research Notes
P Winter-Spring 1987 Vol. 2, No. 1

Arthur A. Richards Darshan S. Padda
President Vice President
Research and Land-Grant Programs


Hatch Act Centennial

Arthur A. Richards
Darshan S. Padda
Vice President
Research and Land-Grant Programs
James Rakocy
Assistant Director
Clara Lewis

Cover Photo: Hydroponically grown lettuce in a recirculating system integrated with fish culture.

From the Director...

From the Director ...

We are pleased to share with you the second issue of the
V.L Perspective, the Agricultural Experiment Station's semi-
annual research report to farm constituents, colleagues and
the public at large.
A perusal of the topics covered in this issue attest to our
dual role of serving both the producers and consumers.
Research reports on white hair sheep, pasture legumes, fish
culture and vegetable varietal testing offer information for
the food producer, whereas the report on ciguatera poison-
ing addresses a public health concern of fish consumers.
The Virgin Islands are passing through challenging times.
The pressure for development is so great that it threatens to
damage the fragile ecosystems and encourage social in-
equality. Agriculture can no longer enjoy a protective shield,
but, instead, must operate as a competitive economic enter-
prise. To pass this test today, agriculture must function as a
business enterprise that is technology-based.
At the same time, the justifiably strong public sentiment
in favor of the small farmer and part-time producer cannot
be ignored. Many of these small farmers may not be able to
participate in strictly "business-like economic develop-
ment," and, yet, they represent an important way of life
which needs to be preserved.
These divergent needs of our community add to the com-
plexities of agricultural development in the U.S. Virgin
Islands. They offer a special challenge to agricultural scien-
tists and community leaders to promote, initiate and
develop systems that are based on social, economic and
technological considerations.

Technical information developed at the Agricultural
Experiment Station and made available to the Virgin Islands
public through this, as well as other publications, will
hopefully contribute towards balanced territorial growth,
promoting food production and, at the same time, conserv-
ing and enhancing our limited natural resources.

Darshan S. Padda
Vice President
Research and Land-Grant Programs

I 'i ,A

Growth and Reproductive
Characteristics in a Flock of
V.I. White (St. Croix) Hair Sheep

By S. Wildeus
Research Animal Scientist

The Virgin Islands White or St. Croix sheep are a breed of
hair sheep that was developed on St. Croix over the past cen-
tury. The animals are white in color, hornless, and show a
body conformation similar to those of other hair sheep in
the Caribbean. Most of these Caribbean breeds are of West
African origin; however, it has been speculated that the V.I.
White sheep were crossed with the British Wiltshire Horn
during some developmental phase of the breed.



Information that is available on the breed under local St.
Croix conditions suggests average mature weights of rams
and ewes to be 119 and 75 lbs., respectively. Lambing rate
estimates range from 1.44 to 1.84 lambs per ewe, with con-
siderable variation between flocks. In order to expand the
information on the V.I. White sheep, a research flock has
been established at the University of the Virgin Islands
Agricultural Experiment Station. The following results rep-
resent data collected on this flock during its first year of
The experimental flock is being housed on approxi-
mately 25 acres, divided into 12 pastures to control grazing
pressure and internal parasites. The predominant forage
species is guinea grass (Panicum maximum), and animals are
stocked at a rate of 2.5 ewes with lambs per acre. As a routine
management procedure, animals are confined overnight to
control predation and larceny. During the duration of the

-- .s, ,


V.I. White Hair Ewes.

Funding Source: Hatch Project #787

study, the flock was exposed to continuous mating. At lamb-
ing, birth weights and litter size are recorded. All lambs are
weaned and weighed at 9 weeks of age. The entire flock is
routinely weighed on a weekly basis.
The body weight of mature ewes averaged 105.5 lbs., but
weights fluctuated throughout the year (Figure 1). Body
weights generally increased throughout the first year of
observation, but showed a slight seasonal increase in June/
July and January/February. The January/February peak in
body weight was associated with increased seasonal rainfall
and pasture growth, while the reason for the June/July peak
is not readily apparent. Only one mature ram is presently
maintained with the research flock, with a body weight of
140 lbs. The average weight of three yearling rams approxi-
mates 100 lbs.
Some indicators of the reproductive performance of V.I.
White ewes are summarized in Table 1. Ewes that lambed
twice during the first year of production had an average
lambing interval of 7.5 months. This would suggest that V.I.
White ewes, with limited exposure to photoperiodic varia-
tion, are capable of producing three lamb crops in a two year
period. Lambing was not distributed evenly throughout the
year, but increased in frequency during June and December





Month of Year

Figure 1. Fluctuations in body weight in mature V.I. White Hair
ewes throughout the year.

Table 1. Lambing performance of mature V.I. White Hair ewes.
Lambing interval 7.5 months
Lambing rate 1.72 lambs/ewe
Weaning rate 1.46 lambs/ewe
Production at lambing 11.0 lbs./ewe
Production at weaning 42.9 lbs./ewe
Frequency of types of births:
single 38%
twins 52%
triplets 10%

l// "



1/ I W 1 I'l1
jmII, ,,~m

(Figure 2). It is not clear at this point if these lambing peaks
are the result of seasonal synchronization.

At lambing, V.I. White ewes produced an average of 1.72
lambs and weaned 1.46 lambs at 9 weeks of age (Table 1).
Lamb loss between lambing and weaning was associated
mostly with triplet births, but also with predation and
abnormal udder formation. The total amount of lamb pro-
duced per ewe lambing was 11.0 lbs. at lambing and 42.3
lbs. at weaning. The incidence of single, twin and triplet
birth was distributed among the flock at 38, 52 and 10%, re-
spectively. This frequency of multiple birth is higher than
that of most breeds of wool sheep, however, not as high as
that reported for the Barbados Blackbelly.
Birth and weaning weights for V.I. White lambs are sum-
marized in Table. 2. Single lambs were significantly heavier



7 20

than twin lambs at both lambing and weaning. Twins
weighed 77 and 74% of single lambs at lambing and wean-
ing, respectively. Differences were also found between male
and female lambs at both lambing and weaning. Ewe lambs
on average achieved weights that were approximately 86%
that of ram lambs. These observations indicate that adjust-
ment factors for type of birth (single, twin or triplet) and sex
of lamb (male or female) will have to be developed for this
breed in order to compare the performance of individual
ewes. More lambing data will have to be collected to calcu-
late valid adjustment factors.
Post-weaning growth patterns, following weaning at 9
weeks of age, were similar between male and female lambs
(Figure 3a). The rate of gain for both sexes was 0.25 lbs./
head/day. Post-weaning growth patterns varied in single,
compared to twin lambs (Figure 3b), with twin lambs show-

Month of year

Figure 2. Annual distribution of lambing in V.I. White Hair ewes under a continuous mating regime.

Table 2. Birth and weaning (9-week) weights of V.I. White Hair lambs.

Single birth Twin birth

male female male female

Birth weights (lbs.) 8.6 7.6 6.8 5.6
Weaning weights (lbs.) 44.5 37.3 31.7 28.7

8 10 12 14
Age (weeks)

16 18

8 10 12 14 16
Age (weeks)

Figures 3A and B. Post-weaning growth in male vs. female and single vs. twin V.I. White Hair lambs.



0 males
* females


ing a more rapid, compensatory post-weaning growth.
Single and twin lambs achieved an average daily gain of 0.18
and 0.26 lbs./head/day, respectively, during a seven week
post-weaning period. All lambs exhibited satisfactory
growth after early weaning at 9 weeks of age, which would
indicate that weaning at this stage may be a feasible manage-
ment tool under local production conditions.
Though the results presented here reflect only data that
have been collected over a period of one year, the informa-
tion gives an indication of the production potential of the

V.I. White sheep. The breed has a high level prolificacy and
good mothering ability, with 85% of the lamb crop being
weaned. The growth rate and mature size is lower than that
of most wooled breeds of sheep, but similar or higher than
in other breeds of hair sheep. A continued effort is being
made to further characterize this breed.

The author would like to acknowledge the assistance of Ms. Kim
Traugott and Mr. Allan Schuster in the collection of the data.

A^ Ni;

VL2'- )*_~ "~

V.I. White Hair Twin Lambs.

Naturally-Occurring Legumes in the Pastures of St. Croix

Michael W. Michaud
Research Agronomist

St. Croix has large areas of both native and improved pas-
tures that are utilized for livestock production. Naturally-
occurring legumes are an important component of these
pastures, affecting the quantity and quality of feed available
to the animals. These indigenous legumes include her-
baceous species as well as woody shrubs and trees.
Though some areas have been planted with improved
forage species, unimproved pastures make the most impor-
tant contribution to the livestock industry. With proper
management, guinea grass (Panicum maximum) tends to be
the most prevalent species, while hurricane grass (Bothriochloa
pertusa) predominates on overgrazed sites. Despite the
dominance of grasses in these pastures, herbaceous legumes
and smaller browse species are generally present.
The extent to which these types of legumes contribute to
pasture composition was quantified by surveys using a step-
point method. Points were selected approximately three
meters apart (five steps) along transect lines that were evenly
distributed throughout each pasture being surveyed. At
each point, a rod was pushed into the ground using the tip of
the foot as a guide (Figure 1). Those plants that the rod
touched at ground level were identified by species and re-
corded accordingly. If the rod touched bare ground, the
closest plant within a forward 1800 arc was recorded.
Results of the surveys are presented in Table 1. The two
most commonly occurring legumes were Desmanthus virgatus,
a small browse shrub, and Teramnus labialis, an herbaceous

P. Joy Michaud
Extension Specialist

vine. These legumes were present in 83% and 77% of the pas-
tures, respectively. In those pastures in which it was present,
Desmanthus was found at 1.0% to 11.0% of the points, while
Teramnus occurred at 0.5% to 10.9% of the points
Other herbaceous legumes found in the native pastures
included Rhyncosia minima, Desmodium sp., Stylosanthes hamata,
and Alysicarpus vaginalis. Alysicarpus and Desmodium were
generally found in the wetter parts of the island, while
Stylosanthes was found in areas dominated by shorter growing
grasses rather than the taller guinea grass.

Figure 1. Step-point method for determining species composition
in pastures.

Funding Source: Hatch Project #784

Table 1. The occurrence of indigenous legumes in the native patures of St. Croix.

Species Percent of pastures in which species is present

Desmanthus virgatus 83
Teramnus labialis 77
Rhyncosia minima 3
-. 30
Desmodium sp J
Stylosanthes hamata 17
Alysicarpus vaginalis 10

The extent to which legumes are found in pastures is Panicum maximum, which normally occurs in well-managed
strongly influenced by grazing management. Surveys were pastures, legumes occurred at more than one quarter of the
performed on two pastures subjected to different grazing points. In contrast, Pasture 2 had been subjected to long-
pressures (Table 2). At the time the surveys were done, Pas- term overstocking and had 15.2 animals per hectare at the
ture 1 had a stocking rate of 5.5 sheep and goats per hectare, time of survey. Its dominant species was hurricane grass,
reflecting the lenient grazing regime to which it had his- while legumes occurred at only 3.5% of the points. Allowing
torically been subjected. While the dominant species was for differences in species composition that would normally

Table 2. Species composition between two native sheep and goat pastures in St. Croix, USVI.

Pasture 1 Pasture 2
Stocking Rate (animals/ha) 5.5 15.2
Panicum maximum 67.5% -
Bothriochloa pertusa 2.0% 87.3%
Leucaena leucocephala 14.5% 1.5%
Teramnus labiahs 7.5% 1.0%
Desmanthus virgatus 4.0% 1.0%
Others 0.5% -
Weeds: 4.0% 9.2%

occur between sites with varying soils and rainfall, it can be
concluded that stocking rates (animals per unit area of land)
affect the legume composition in native pastures.

In addition to the herbaceous and smaller shrub
legumes, larger shrubs and trees make an important con-
tribution to pasture composition. One of the most impor-
tant of these species is Leucaena leucocephala, known locally as
tan-tan. It was found in two-thirds of the pastures surveyed.
When ungrazed or uncut for long periods of time, it can
grow to 9 meters in height. It is, however, particularly palat-
able to all classes of ruminant livestock, and its growth is
limited to 2 meters or less when grazing is imposed. In addi-
tion, pastures are occasionally cut back with a shredder,
which further checks the growth of Leucaena.
The pasture surveys quantified the presence of Leucaena in
either one of two ways. In those pastures where it was short-
statured or below the grass canopy, it was included in the
step-point method used to study the other forage species.
This technique was used to characterize Leucaena in the pas-
tures described in Table 2. With a lenient grazing regime, it
comprised 14.5% of the points. However, increasing the
stocking rate decreased its presence to only 1.5%, thus
demonstrating its sensitivity to management.

In the pastures where Leucaena growth was above the grass
canopy, actual populations were determined by counting
those plants whose main stalk fell within 0.5 meters of either
side of the transect line used with the step-point method.
This was the more frequently employed technique, and pop-
ulations were found to range between 100 and 12,000 plants
per hectare.
Acacia, locally known as casha, another large woody
legume, was found in almost 90% of the pastures. In the dry
areas, the most common species is A. tortuosa, while A. mac-
rancantha tends to be more common in wetter areas. Pop-
ulations averaged 658 plants per hectare and reached over
5,000 plants per hectare in one pasture (Table 3).
Unlike Leucaena, Acacia is an undesirable species.
Although goats occasionally use it for browse, cattle do not
consume it. Its large thorns (Figure 2) and habit of branch-
ing from the base make the pasture underneath them inac-
cessible to livestock (Figure 3). Diameters of the Acacia
canopies were measured, and it was found that up to 30% of
the land was covered (Table 3). Unless Acacia is controlled,
the amount of pasture available to animals can be signifi-
cantly reduced.

Table 3. The presence of Acacia sp. in the native pastures in St. Croix, USVI.

Frequency of Occurrence (%) 90
Number of shrubs/hectare: Mean 658
Range 0 to 5755
% land covered by shrubs: Mean 5
Range 0 to 26

Figure 2. Branch of Acacia showing thorns.

S. a .t. mAk p i o pr. i. ri

Figure 3. Acacia can make large portions of the pasture inaccessable to grazing livestock.

Though the native pastures make the largest contribution
to animal production on St. Croix, small areas have been
planted with improved grasses. Indigenous legumes are
found in these pastures to varying degrees, sometimes mak-
ing significant contributions to their composition. One such
example is a buffel grass (Cenchrus ciliaris) pasture surveyed
by the step-point method (Table 4). Legumes comprised
almost 40% of the points, with Desmanthus and Teramnus the
most prevalent species.
While grasses form the basis of pastures on St. Croix,
legumes are an important component. Desirable her-
baceous and woody species are often present in significant

amounts and contribute much to animal production. Well-
managed pastures require that Acacia species be controlled,
since their presence means a reduction in feed available to
the livestock utilizing them. When proper stocking rates are
used, a species composition favoring the presence of
legumes will be established, resulting in pastures of long-
term productivity.

Thanks must be given to the many farmers who have allowed us on
their land to conduct the surveys. However, special acknowledgement is
given to Allan and Henry Schusterfor their ideas on pasture manage-
ment and permission to collect data on their farm.

Table 4. Forage species found in a pasture planted with "Common" buffel grass (Cenchrus ciliaris), St. Croix, USVI

Species %

Cenchrus ciliaris 32.8
Panicum maximum (local) 9.0
Bothrichloa pertusa 3.0
Desmanthus virgatus 18.9
Teramnus labialis 12.4
Clitoria ternatea 3.0
Rhyncosia minima 2.5
Stylosanthes hamata 2.5

Other 15.9

Ciguatera Fish Poisoning
in the Eastern Caribbean

By J.P. McMillan
Associate Professor of Biology

Seafood poisonings occur world-wide, but the highest
incidence and greatest variety are found in tropical waters.
The seriousness of this public health and economic problem
is aggravated by the fact that most animals implicated in
poisonings dwell in shallow water and are thus the most
accessible marine food resource. Additionally, there is an
environmental feature to the problem because a disturbance
of the coral reef ecosystem by human activities often results
in the proliferation of toxic organisms.
Among the many kinds of seafood poisonings, ciguatera
is the most widespread and serious problem. It has for cen-
turies afflicted people, particularly islanders, living by tropi-
cal seas around the world. Ciguatera poisoning results from
the consumption of fish which contain ciguatoxin (CTX), a
neurotoxin produced by reef-associated microorganisms
called dinoflagellates. When the dinoflagellates are con-
sumed, the CTX enters the food chain where it accumulates
at each link, becoming most concentrated in predatory fish,
those which commonly poison humans. Although rarely
fatal, a ciguatera intoxication is usually debilitating, with gas-
trointestinal manifestations initially and complex neurologi-
cal symptoms following for days, weeks, months, and
even years.
The symptoms of ciguatera usually occur within two to
twelve hours after eating ciguatoxic fish. The gastrointestinal
symptoms are similar to food poisoning: abdominal pain,
nausea, vomiting and diarrhea. However, because CTX is a
neurotoxin, it can be distinguished from spoilage poisoning
by the symptoms affecting the nervous system. These may
include itching or tingling of the lips, tongue, mouth, skin,
palms and soles; aching and weakness in muscles and joints;

and the sensation that hot is cold and cold is hot. There is no
test for ciguatera and its diagnosis is made on the history of
the fish ingestion and the symptoms manifested. The
symptoms may recur after the initial intoxication, becoming
less frequent and less pronounced over time. The severity of
the intoxication depends upon the toxicity of the fish, the
amount consumed, and the body size and health of the vic-
tim. No specific, effective treatment is available.
There are probably hundreds of cases annually in the
Eastern Caribbean. The varieties of fish most frequently
implicated snappers, grouper, kingfish, jacks are those
most widely esteemed, highly abundant, and, therefore,
most sought. And despite local folklore, toxic fish cannot be
discriminated from nontoxic ones on the basis of appearance,
smell, taste or texture. No simple, reliable and inexpensive
test is yet available. In the opinion of experts from local,
regional and international agencies, ciguatera is the greatest
single impediment to the development of the inshore fishery
because of its significance as a public health problem.
From the foregoing, the urgency for research is apparent
and certain objectives are imperative. A test to determine the
ciguatoxicity offish is clearly needed, as is a rational therapy
for the treatment of ciguatera intoxication. For many
reasons, however, progress toward these objectives has been
steady but slow. The problem occurs circumtropically,
affecting island populations primarily, far from the
mainstream of global society and technology. Another
impediment is that CTX, while an extremely potent toxin, is
present even in very toxic fish, on the order of parts per
billion. This causes a supply problem for research and
makes CTX difficult to detect chemically in fish because
there is so little there for analysis. In fact, the molecular
structure of CTX has yet to be completely elucidated,
although it is known to be a heat stable polar lipid with a
molecular weight of about 1,112.
Our research activities are designed to take advantage of
our location in the tropics where ciguatera occurs, and to
extend our capabilities through collaboration with scientists

Funding Source: Hatch Project #786

Figure 1. A line drawing taken from scanning electron micrographs of Gambierdiscus toxicus, the Dinoflagellate recently implicated in the
biogenesis of ciguatoxin (after Dr. F.J.R. Taylor, University of British Columbia).


Cells Stored in Methanol
Boiling Methanol
Discard Residue
Discard Residue

Water Soluble
Extract With Butanol
Water Soluble Butanol Soluble
Add Acetone
Chill (-95C)
Cold Filter
Filtrate B Precipitate B (Toxic)

Add Water
Extract With Chloroform

Chloroform Soluble
Add 80% Methanol
Extract With Hexane
Hexane' Soluble Methanol Soluble
Add Acetone
Chill (-95-C)
Cold Filter
Filtrate A Precipitate A (Toxic)

Figure 2. Extraction and preliminary purification procedure for lipid-soluble (PPT-A) and water-soluble (PPT-B) toxins from
Gambierdiscus toxicus.

and technological resources at other institutions. Studies on
the mode of action and structure of CTX require a supply of
the toxin. We obtain fish samples locally that have caused
ciguatera or are suspected of harboring CTX because of
their species, size and catch location. From these, we extract,
purify and bioassay CTX for our own and our collaborators'
research activities.
Recent experimental work involved the weekly adminis-
tration to mice of sublethal doses of extracts from ciguatoxic
fish flesh implicated in human ciguatera cases, or doses of
nontoxic, control fish extracts. The CTX-treated mice had
significantly lower body weights, lower body temperatures,
and higher ciguatoxicity sign ratings than controls. The
effects of each weekly dose of CTX were consistent in
magnitude and duration, with no progressive increase or
decrease in response over the course of the eight week study.
This is in contrast to reports of sensitization by human
ciguatera victims who have been affected by more than one
intoxication. Histopathology revealed no selective site of
toxicity in the mice. At the end of the study, CTX-treated
mice succumbed to a single lethal dose of CTX. No CTX
antibodies were detected in the sera of the repeatedly CTX-
treated mice. Collectively, the findings in these experimental
animals are consistent with absence of developed immunity
to ciguatera in humans.
Research on the biological source of the toxin(s) which
cause ciguatera, begun a decade ago by scientists in the

South Pacific, has lead to the identification of Gambierdiscus
toxicus, a reef-associated bottom-dwelling dinoflagellate. We
have collected large samples of G. toxicus from the Caribbean
Sea. When extracted, G. toxicus yields two toxic components
which differ in their initial solubilities, one is lipid soluble
(PPT-A) and the other water soluble (PPT-B). Both are heat
stable and precipitate in cold acetone. Ciguatoxic fish
extract (CTX) is water insoluble but does not precipitate in
cold acetone. PPT-A, PPT-B and CTX, however, produce
signs in the mouse bioassay which are virtually indis-
tinguishable, including a pronounced lowering of body tem-
perature. In a number of chromatographic systems, PPT-A
and PPT-B show strong similarities but both differ markedly
in comparison to fish CTX. The toxins ofG. toxicus thus may
undergo structural transformation when passed through the
food web to ultimately become the CTX in fish that causes
ciguatera poisoning in humans.
Ciguatera is more than a research problem. We attempt to
deal with the public health and economic aspects of
ciguatera by an advisory outreach effort to the community
and region. Through newspaper articles and pamphlets,
radio and TV appearances, talks to civic groups, a ciguatera
"hotline," and consultations with fishermen, merchants,
restaurateurs, public health and government officials, we
provide the facts on ciguatera. In doing so, we seek to dispel
folklore, avoid sensationalism, and offer the basis for
informed choices and action.

Yield Results of Vegetable
Varietal Evaluation Trials
in the U.S. Virgin Islands
By Arthur C. Petersen, Jr.
Vegetable Specialist
Tomatoes, peppers and eggplants are as popular in the
U.S. Virgin Islands as in any other part of the world. These
three Solanaceous crops are widely used in many native dis-
hes, and the demand for them is continuously high. Cur-
rently, about 80% are imported from neighboring Eastern
Caribbean Islands and the U.S. mainland. Because of
transportation costs, the price of imported vegetables have
been climbing steadily. The high price for imported pro-
duce has stimulated both large and small-scale vegetable

production. Vegetable production in the Virgin Islands is
limited by soil, water, and climatic problems, as well as by
plant diseases and insect pests. Another major factor limit-
ing local production has been the high cost of labor. Because
most vegetable seeds are purchased from temperate seed
suppliers, choosing the proper variety for local conditions is
fundamental to success regardless of production scale.
The climatic conditions of the Virgin Islands during the
winter season are favorable to the production of bumper
crops. Winter vegetable production in the Virgin Islands has
great potential not only for self-sufficiency but also for the
export market.
To determine which tomato, pepper or eggplant varieties
are best adapted to the Virgin Islands environment, different
varieties were tested annually at UVIAES. In addition to test-
ing for yield, a variety of entries were also evaluated for heat
and drought tolerance for breeding purposes. This report is

Table 1. 1986 estimated yield of pepper varieties.'

Variety: Marketable yield (kg/hectare) Percent Marketable yield (%) Fruit size (g)

Hybrid Jupiter 51,300 95.2 112
California Wonder 45,800 93.2 91
Hybrid Acx-841715 45,400 95.5 93
Yolo Wonder 41,000 94.8 111
Early California 40,600 93.2 92
Giant Resistant #4 39,700 91.7 94
Cubanelle 38,900 96.3 51
Hybrid Hy-fry 36.400 95.7 63
Hungarian Hot Wax 36,100 97.2 34
Hybrid Glory 30,900 93.3 80
Sweet Banana 27,100 95.7 41
Hungarian Sweet Wax 25,700 90.4 80
Cayenne Large Thick 24,700 87.0 23

'Values are means of three replications per variety.

Funding Source: Hatch Project #684

Table 2. 1986 estimated yield of eggplant varieties'

Variety: Marketable yield (kg/hectare) Percent Marketable yield (%) Fruit size (g)
Burpee Hybrid 102,600 88.4 425
Midnite 100,200 91.3 461
Bybird Black Jack 89,700 79.6 459
Black Jet 83,000 90.3 385
Black Beauty 80,700 68.3 668
Hybrid Epic 80,000 89.1 332
Rosita 78,300 83.4 327
Florida Market #10 76,000 89.5 444
Dusky Hybrid 75,300 87.0 316
Super Hybrid 51,007 62.8 397
Hybrid Beauty 51,007 77.7 364
Long Purple 48,900 68.3 220
Hybrid Imperial 34,300 65.5 210

1Values are means of three replications per variety.

a summary of the results obtained from such tests in
A series of three vegetable variety trials were conducted at
VIAES between August, 1983 and August, 1986 on Freden-
borg clay soil with a pH of 7.5 to 8.0. The field was
ploughed, disked, and banked with 30-cm high ridges 90 cm
apart and partitioned into 1.8 x 6-m plots. Each plot consist-
ed of 39 plants arranged in three rows. Plant spacing within
rows was 46 cm apart for pepper and eggplant and 61 cm
apart for tomatoes. Weed control was accomplished using
pre-emergence application of Round-UpTM or DacthalTM
along with mechanical cultivation and hand-hoeing. A ran-
domized complete-block design with three replications
was used.
Seeds were obtained from various sources. Transplants
were started in Jiffy-SevenTM peat pellets and were main-
tained in a 70% shaded greenhouse for a week to provide

uniform seedling establishment. Seedlings were thinned to
one per peat pellet and were maintained under full sunlight
until plants were six weeks old. Seedlings were watered daily
and fertilized bi-weekly with 400 ppm of Peter's 20:20:20
commercial fertilizer.
The vegetable crops were irrigated using a drip irrigation
system when needed to prevent moisture stress to crops.
Plants received a fertilizer (amonium sulfate) application at a
rate of 168 kg/hectare on the second week after transplanting
and a second application at initiation of flowering. Insect
pests and diseases were controlled with recommended rates
of BravoTM, LannateTM, DiazionTM and KocideTM during the
course of the experiment. Marketable yields were harvested
in 6 to 8 pickings for all experiments.
Yields were determined by hand harvesting mature fruits
from the center row of each three-row plot at 7 to 10-day
intervals, depending on the rate of fruit growth and develop-
ment. Peppers were harvested when fruits were about 8 cm

or greater in length. Tomatoes were harvested at the pink
stage of maturity and eggplant when fully matured. All
vegetables were culled and weighed in the field. Fruit harvest
was discontinued when fruit quality was non-marketable.
Marketable yield and some yield attributes of pepper are
summarized in Table 1. Yield in the tests ranged from 51,300
to 24,700 kg per hectare. HybridJupiter, California Wonder,
Hybrid Acx-841715, Yolo Wonder and Early California were
the best yielders. Specialty types such as Cubanelle, Sweet
Banana, Cayenne and Hungarian Yellow Wax also per-
formed well in the trials. Blossom-end Rot and Tobacco
Mosiac Virus were the major production problems of note,
especially towards the end of the growing seasons; but,
yields were not significantly reduced. The bell pepper
varieties had a greater incidence of these diseases.
There were significant differences in yield among the
eggplants (Table 2). Burpee Hybrid and Midnite, with yields

of 102,600 and 100,200 kg per hectare respectively, were the
most productive varieties in the trials. Hybrid Black Jack,
BlackJet, Black Beauty and Hybrid Epic also performed well
in the trials. The major insect pests were aphids and mites,
which occurred mainly at the end of the productive
Yield data for tomatoes are summarized in Table 3. Hy-
brid Revolution, Hybrid Liberty, and Hybrid Count II were
the best yielders. The major insect pests were the fruitworm
(Heliothis spp.), and the major disease problem was Early
Blight. Some of the yield differences were probably due to
differences in their tolerance to Early Blight. None of the
varieties included in the trial displayed any resistance to
the disease.
Results from these trials will be useful in developing the
recommended list of pepper, eggplant and tomato varieties
for production in the U.S. Virgin Islands.

Table 3. 1986 estimated yield of tomato varieties'

Variety: Marketable yeild (kg/hectare) Percent Marketable yield (%) Fruit size (g)
Hybrid Revolution 57,700 91.0 179
Hybrid Liberty 52,500 89.7 166
Hybrid Count II 50,100 90.6 191
Hybrid Celebrity 48,100 93.5 194
Hybid Mountain Pride 46,600 92.6 190
Hybrid President 46,100 90.7 196
Calypso 44,600 89.2 209
Hybrid Floramerica 43,600 87.0 227
Hybrid Duke 42,800 89.1 197
Hybrid Independence 41,000 89.1 191
Hybrid Peto Pride 40,400 93.5 125
Hybrid Better Boy 29,100 86.0 180
ACE 55VF 26,100 89.0 249
'Values are means of three replications per variety.

Integrating Fish Culture and Vegetable Hydroponics:
Problems and Prospects

James E. Rakocy
Research Aquaculturist

The very limited supply of fresh vegetables and fish on
semiarid Caribbean islands and the heavy reliance on
imported products of frequently poor quality have provided
the impetus for studying the integration of fish and vege-
table production in water reuse systems at UVIAES. Com-
bining these diverse agricultural enterprises would maxi-
mize the local production of food per unit of water con-
sumption. Additionally, fish culture wastewater would pro-
vide the majority of nutrients required by the plants while
nutrient uptake by the plants would help in purifying the
wastewater, which could possibly lead to higher production
levels of fish.
Integrating fish culture with vegetable hydroponics
creates special problems. One of these problems is the large
amount of sludge that is generated from fish waste. In recir-
culating fish culture systems, sludge is removed by the pro-
cess of sedimentation in conical or rectangular clarifiers.
Although the clarifier removes most of the sludge, a certain
amount of sludge remains suspended as small colloidal par-
ticles. Hydroponic systems frequently utilize fine support
medium such as sand or gravel. When these media are used
in integrated systems, they tend to become clogged over
time with a buildup of sludge. Even the nutrient film tech-
nique faces the danger of becoming fouled with the forma-
tion of a sludge blanket. Excessive sludge buildup has a
deleterious effect on plant growth because it blocks the flow
of water and creates anaerobic zones.
Integrated systems require good water clarification and
specially designed hydroponic tanks. Research at UVIAES
has shown that reciprocating gravel biofilters with a false
bottom perform well as hydroponic tanks. Reciprocating

Ayyappan Nair
Assistant Aquaculturist

biofilters continuously flood and drain to alternately expose
nitrifying bacteria to wastewater and air. This cycle is also
beneficial to plant roots. The gravel will not clog with sludge
if it is suspended on a sturdy wire mesh that is supported
about 7.5 cm off the tank floor. It is best to use a shallow
layer of gravel (20 cm) and a large grade (2.5 cm). To prevent
a sludge blanket from forming on the tank floor, some fish
must be placed in the hydroponic tank. Their swimming
action keeps the sludge suspended and flowing through the
system until it is removed by the clarifier.

There are some problems associated with the use of
gravel as a hydroponic substrate. Its weight requires strong
and expensive tanks. It is also very difficult to plant in coarse
gravel. A better hydroponic substrate is floating sheets of
styrofoam with holes for small plastic baskets to support the
transplants (Figure 1). Fish are still needed to prevent sludge
accumulation on the tank floor, and a screen, though less
sturdy, is still needed to prevent the fish from having access
to the plant roots. Some species such as tilapia will eat

Another major problem with integrated systems is the
buildup of dissolved nutrient salts to levels that are toxic to
plants. In recirculating systems at UVIAES with a total water
volume of 15 m3, an initial salt concentration of approxi-
mately 100 mg/liter reached 2,000 mg/liter after 150 kg of
fish feed were consumed. These were closed systems in
which daily makeup water was added at a rate of 1% of the
total system volume. Tomato plants begin to exhibit signs of
toxicity when the salt level exceeds 2,200 mg/liter.

Funding Source: Hatch Project #692

Figure 1. Hydroponically grown lettuce in a recirculating sy

Large dilutions would be required to prevent salt toxicity,
but this approach could consume too much water. The rate
of salt accumulation would be significantly decreased by
enlarging the plant growing area so that nutrient uptake by
the plants removes most of the salts. The optimum ratio be-
tween the plant growing area and the feeding rate has yet to
be established.
Fish feeds do not contain adequate levels of all the nu-
trients required for plant growth. Iron and potassium must


integrated with fish culture.

periodically be supplemented. During system startup,
plants also benefit from the addition of phosphorous. A
recent study has shown that calcium is also deficient in sys-
tems with styrofoam substrates but not in systems with
gravel substrates composed of sedimentary rock (Figure 2).
If plant growing areas are enlarged to decrease salt buildup,
additional nutrients may have to be supplemented.
Closed fish culture systems have traditionally relied on
some form of calcium carbonate such as oyster shells or

tVI O.



*-- styrofoam


0 14 28 42 56 70
Figure 2. Calcium concentrations (mg/liter) in recirculating fish
culture systems containing gravel or styrofoam substrates for
vegetable hydroponics.

limestone to neutralize acid formed by ammonia removal
during the process of nitrification. As carbonate ions neu-
tralize the acid, high concentrations of calcium develop.
Calcium carbonate substrates are not recommended for
hydroponic systems because high calcium levels will precipi-
tate phosphorus and make it unavailable for plant nutrition.
Therefore, closed integrated systems require some other
form of base to neutralize acid. Research at UVIAES has
shown that potassium hydroxide is an ideal base for
integrated systems because it not only neutralizes acid but
also supplements potassium, which is required by plants in
very high concentrations. Potassium hydroxide pellets are
added once every two days as the pH approaches 6. Hydrox-
ides of calcium and magnesium may be needed if potassium
levels become too high because plants require a certain
balance between potassium, calcium and magnesium ions
for maximum growth.
Another problem with integrated systems is the use of
pesticides to control insect and disease outbreaks on the

Figure 3. Plan view of a recirculating system for tilapia culture and vegetable hydroponics: A, rearing tank; B, outlet; C, clarifier; D, baffle; E,
valve; F, sump; G, upper hydroponic biofilter; H, lower hydroponic biofilter; I, reservoir; J, pump; K, water inlet; L, overflow outlet; M, return
inlet; N, drain line; 0, canopy.

Table 1. Hydroponic production of four varieties of tomatoes in a recirculating fish culture system during a 16-week

Cherry Challenger Vendor Floradade Sunny

Fruit production*
no/plant 163 31 79 83
kg/plant 2.9 3.7 9. 10.1
kg/m2 15.8 18 16.3 18.4
Marketable tomatoes (%)* 97 88 96 97
Survival (%) 100 81 100 100

*Does not include unripened tomatoes.

Table 2. Hydroponic production of varieties of lettuce, pac choi and Chinese cabbage in a recirculating fish culture system
during a 16-week experiment.*

Lettuce Pac Choi Chinese Cabbage
Buttercrunch Summer Bibb Pac Choi Le Choi 50-Day Hybrid Tropical Delight

no/m2/crop 24.7 24.4 18.3 18.0 18.4 18.2
kg/m2/crop 4.7 4.3 7.6 8.7 11.3 10.6
Mean size (g)+ 193 180 442 508 638 589
Mean survival (%) 99 99 97 94 96 97

*Based on four crops except pac choi (3 crops).
+ Includes only edible portion of plant.

vegetables. Most pesticides are very toxic to fish. If pesticides
are used, a small portion will invariably reach the culture
water either through drift or leaf drip onto the hydroponic
media. Integrated systems need pesticides that are relatively
non-toxic to fish and break down quickly in water. One such
pesticide is acephate, a systemic organophosphate. Effective
biological pest management is needed for integrated
In spite of the problems, integrated systems have poten-
tial for commercial production of fish and vegetables in
regions where agriculture is severely limited by a shortage of
freshwater. Very good results have been obtained with an
experimental unit at UVIAES (Figure 3). The system is sim-
ple to operate, reliable and productive. It consists of a 12.8-
m3 rearing tank, a 1.9-m3 clarifier, a 1.4-m3 reservoir and
two reciprocating gravel biofilters (2.1 m3 each) that also
serve as hydroponic beds. The total plant growing area is
13.8 m3. Water for the system is obtained by harvesting rain-
water with a vinyl catchment.

The system has been used for the production of tilapia,
tomatoes and several types of leafy green vegetables. The sys-
tem is capable of producing 50,000 sex-reversed fry
monthly, 8,000 fingerlings (20 g) in 3 months or 400 kg of
marketable tilapia in 6 months. Water consumption per kg
of tilapia production is approximately 87 liters, which is less
than 1% of the water required for raceway production and
only 10 to 20% of the water required for pond production.
Good yields of tomatoes, lettuce, pac choi, and Chinese cab-
bage have been obtained in variety trials (Tables 1 and 2).
The problems that arise from integrating fish culture with
vegetable hydroponics have proven to be challenging but
not insurmountable. Through water reuse and resource
recovery, integrated systems have demonstrated potential
for expanding food production in areas with scarce water
resources and a need for food self-sufficiency.


3 3138 00175 2566

Disclaimer Statement

V.I.Perspective is published biannually by the University of the Virgin Islands Agricultural Experiment Station. Contents of this publication constitute
public property. The written material may be reprinted if no endorsement of a commercial product is stated or implied. Please credit the University of the
Virgin Islands Agricultural Experiment Station. Trade names or products occasionally are printed. No endorsement of products or firms is intended, nor is
criticism implied of those not mentioned.
The University of the Virgin Islands, including the Agricultural Experiment Station, is committed to the policy that all persons shall have equal access to
its programs, facilities, and employment without regard to race, religion, color, sex, national origin, handicap, age or veteran status.

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