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B. Central America - PD/A CRSP 14th Annual Administrative Report
Pond Dynamics/Aquaculture CRSP
Fourteenth Annual Administrative Report
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IV. Abstracts of Technical Reports

B. Central America Abstracts

Effect of Diet Protein on Food Conversion and Nitrogen Discharge during Semi-Intensive Production of Penaeus vannamei during the Wet Season

Interim Work Plan, Honduras Study 1 (Part I)

David R. Teichert-Coddington, Bartholomew Green, and Claude E. Boyd
Department of Fisheries and Allied Aquacultures
Auburn University
Auburn, USA

John L. Harvin and Rigoberto Rodriguez
Grupo Granjas Marinas Sn. Bernado, SA
Choluteca, Honduras

Delia Martinez and Eneida Ramirez
Laboratorio de Calidad de Agua
La Lujosa, Choluteca, Honduras

Abstract

The objective of this study was to evaluate the effect of diet protein level and feeding rate on shrimp yields, food conversion ratio (FCR), and nitrogen effluents. Earthen ponds ranging in area from 0.7 ha to 2 ha were stocked with Penaeus vannamei post larvae at 24/m2. The larvae were fed high or low rates of a commercially formulated pellet containing 20% or 40% crude protein, respectively. Protein level or feeding rate did not significantly effect gross shrimp yield or mean shrimp size. Feeding rate, but not protein level, significantly affected FCR, which was higher at the higher feeding rate. No interaction was detected between protein level and feeding rate for yield, mean shrimp size, or FCR. A high protein diet fed at a low rate did not influence production any more than a low protein diet fed at a low rate. Mean material exchange in treatment ponds was negative (greater mass discharge than mass intake) for total nitrogen, total phosphorus, chlorophyll-a, and BOD2, and positive for dissolved inorganic nitrogen. There waa net discharge of filterable phosphate at the high feeding rate and a net accumulation at the low feeding rate. More total nitrogen was introduced into ponds by shrimp, water, and feed than was removed from ponds as harvested shrimp and discharge water. The mean treatment difference between input and output nitrogen was significantly higher at the high feeding rate than the low feeding rate. Protein level had no significant effect on the nitrogen balance.

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Effect of Diet Protein on Food Conversion and Nitrogen Discharge during Semi-Intensive Production of Penaeus vannamei during the Dry Season

Interim Work Plan, Honduras Study 1 (Part II)

Bartholomew W. Green, David R. Teichert-Coddington, and Claude E. Boyd
Department of Fisheries and Allied Aquacultures
Auburn University
Auburn, USA

John L. Harvin, Hector Corrales, and Rafael Zelaya
Grupo Granjas Marinas, SA
Choluteca, Honduras

Delia Martinez and Eneida Ramirez
Laboratorio de Calidad de Agua
La Lujosa, Choluteca, Honduras

Abstract

Results of previous research in Honduras have demonstrated that shrimp production is similar at feed protein levels ranging from 20% to 40%, when shrimp are stocked at densities ranging from 5 to 11/m2. Additionally, a 50% reduction in the feeding rate did not affect dry-season shrimp production. The objective of this experiment was to determine the effect of dietary protein and feeding rate on feed conversion and nitrogen discharge in semi-intensive production of Penaeus vannamei. Twelve 1.67-ha earthen ponds located on a commercial shrimp farm were used in a completely randomized study design. Three treatments, with four replicates per treatment, were tested: a 20% and 30% protein feed applied at 50% of the feeding curve, and a 20% protein feed applied at 75% of the feeding curve. Ponds were stocked with hatchery-produced post-larval (PL) Penaeus vannamei to achieve a final stocking rate of approximately 80,000 shrimp/ha. Ponds were harvested 87 days after stocking. Gross yields of head-on shrimp ranged from 412 to 534 kg/ha for the 87-day production period. Feed protein content did not affect gross shrimp yields significantly; however, gross yield of whole shrimp fed the 20% protein feed was significantly greater at the 75% feed curve rate compared to 50% feed curve rate. Feed conversion ratios (FCR) were close to one, and were significantly lower with the 30% protein feed and at the 50% feed rate. Nitrogen and phosphorus additions to ponds as feed were significantly greater with the high-protein feed and with the low-protein feed at the higher feed rate. Significant differences in nitrogen or phosphorus concentrations in water discharged from ponds were not detected among treatments.

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Estuarine Water Quality

Interim Work Plan, Honduras Study 2

David R. Teichert-Coddington, Bartholomew Green, and Claude E. Boyd
Department of Fisheries and Allied Aquacultures
Auburn University
Auburn, USA

Delia Martinez and Eneida Ramirez
Laboratorio de Calidad de Agua
La Lujosa, Choluteca, Honduras

Abstract

The objective of this study was to monitor estuarine water quality in order to detect trends over time, and evaluate the impact of shrimp farming on water quality. Water samples were collected at intake pumps of shrimp farms. Samples were taken every 1 to 2 weeks from at least 12 sampling sites distributed over six estuaries in the shrimp farming area of southern Honduras. Water samples were analyzed and summarized according to estuarine type, location, season, month, and year for total settleable solids, total ammonia nitrogen, filterable reactive phosphate, chlorophyll-a, total alkalinity, salinity, and BOD7. Data collection and analyses are in progress. A preliminary analysis of total nitrogen was completed for El Pedregal estuary. Nitrogen input as feed was greatest during the rainy season due to increased shrimp growth in this season; however, there was no accumulation of nitrogen from heavy feeding because of flushing by runoff. During the dry season, a period of relatively light feeding, nitrogen concentrations tended to increase, because of insignificant freshwater input and low exchange with bay water. Overall total nitrogen concentration did not increase with time, primarily because runoff from rainfall flushes the estuaries yearly.

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Sex Reversal of Tilapia: 17a-Methyltestosterone Dose Rate by Environment and Efficacy of Bull Testes

Interim Work Plan, Honduras, Study 4

Ronald P. Phelps, Leonard L. Lovshin, and Bartholomew W. Green
Department of Fisheries and Allied Aquacultures
Auburn University
Auburn, USA

Abstract

Sex reversal of newly hatched tilapia generally is accomplished via oral administration of 17a-methyltestosterone (MT), which has been incorporated into a starter fish feed at 60 mg MT/kg feed. Other investigators have reported sex reversal of tilapia at dose rates less than 60 mg MT/kg feed; however results from some of these studies are inconsistent, and it is difficult to separate treatment environment effects. Naturally occurring sources of testosterone may be an alternative to using a synthetic androgen, which also is an anabolic steroid, for tilapia sex reversal. Bull testes are a by-product of the beef industry in the US, and are a potential source of dietary testosterone for tilapia sex reversal. The objectives of this research were: 1.) to determine the efficacy of different dosage rates of MT for sex reversal of fish treated in different environments, and 2.) to evaluate the potential of freeze-dried bull testes as a dietary source of testosterone for tilapia sex reversal. Newly hatched Nile tilapia (Oreochromis niloticus) were stocked at 8 fry/l into 80-l glass aquaria located inside a hatchery building or into hapas suspended in 20-m3 outdoor concrete tanks. Trout chow was the carrier for MT, which was incorporated into the feed at 0, 10, 20, 30 and 40 mg MT/kg of feed. Frozen bull testes, obtained from a meat packing plant, were freeze-dried, ground, and mixed with trout chow either in a 1:1 or 1:3 freeze-dried testes: trout chow ratio. The use of freeze-dried bull testes (BT) as a source of testosterone was not effective in producing tilapia populations of 95% or greater males. The percentage of males ( 54%) in populations fed a ration containing 25% BT did not differ from non-treated populations (52.4%). The percentage males (64.8%) obtained when BT composed half of the ration was significantly greater than non-treated populations. Indoor and outdoor treatments did not affect the ability of 17a-methyltestosterone to alter the sex ratio of tilapia. Greater than 97% male populations were obtained at dose rates of 15 mg,
30 mg, 45 mg and 60 mg MT/kg feed when fish were treated in indoor aquaria or outdoor hapas.

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Study of Chemical Variables in Two Estuaries of Southern Honduras

Interim Work Plan, Honduras Study 3 (Part I)

Miguel Antonio Mosquera
Department of Natural Resources and Conservation Biology
Panamerican Agricultural School
Zamorano, Honduras

Abstract (Printed as submitted)

Two major shrimp producing estuaries, El Pedregal and the San Bernardo, were sampled weekly at high and low tides for five weeks during the rainy season of 1995. The sampling period spanned a lunar cycle when tidal levels fluctuated. Water samples were collected from the surface, mid depth, and near the bottom. Samples were taken at four stations along a longitudinal transact of each estuary that discharges into the Gulf of Fonseca. Water was analyzed for BOD5, total phosphorus, filterable phosphate, nitrate nitrogen, total nitrogen, total ammonia, chlorophyll-a, and total suspended solids. El Pedregal estuary had significantly higher concentrations of organic material and more nutrients than the San Bernardo. Mean nutrient concentrations were significantly higher at low tide than at high tide, probably because estuarine water was diluted with relatively pristine gulf water during the high tide. Nutrient concentrations were not predictably stratified along the lengths of estuaries. There was no apparent pattern between nutrient concentrations and lunar phase in either estuary. High freshwater inflow from rainfall probably masked lunar and longitudinal effects of estuarine hydrology. There were few water quality differences between the surface and bottom of estuaries, except for total settleable solids which tended to be higher at the bottom. Otherwise, high tidal fluctuation kept water vertically mixed in the main estuarine channels.

(This thesis was in partial fulfillment of the Ingeniero Agrónomo degree, Escuela Agricola Panamericana, Zamorano, Honduras. Abstract translation by David Teichert-Coddington)

 

Physico-Chemical Characterization of Two Estuaries of Southern Honduras during the Rainy Season

Interim Work Plan, Honduras Study 3 (Part II)

José Antonio Serrano
Department of Natural Resources and Conservation Biology
Panamerican Agricultural School
Zamorano, Honduras

Abstract (Printed as Submitted)

Two major shrimp producing estuaries, El Pedregal and the San Bernardo, were sampled weekly at high and low tides for five weeks during the rainy season of 1995. The sampling period spanned a lunar cycle when tidal levels fluctuated. Dissolved oxygen, temperature, and salinity were recorded at 50-cm intervals from surface to bottom. Measurements were taken at seven stations in El Pedregal and six stations in the San Bernardo. The stations were located along a longitudinal transect of each estuary that discharges into the Gulf of Fonseca. Both estuaries are influenced by rivers. The Black River (Rio Negro) enters the San Bernardo at its head, and the Choluteca River enters the El Pedregal near its mouth. Salinity of the San Bernardo was less than that of the El Pedregal due to river flow through the estuary. In both estuaries, but particularly in the San Bernardo, salinity increased closer to the gulf because of intrusion by higher salinity gulf water. Mean estuarine salinity was significantly higher during high tide. The distance upstream that gulf water exchanged with estuarine water could be demonstrated from the change in salinity at various depths during tidal exchange. Dissolved oxygen concentrations of estuarine water increased with greater influence of the gulf. In both estuaries, dissolved oxygen concentrations were significantly higher near the gulf than upstream. Dissolved oxygen was also significantly higher during the high tide, and during the new moon.

(This thesis was in partial fulfillment of the Ingeniero Agrónomo degree, Escuela Agricola Panamericana, Zamorano, Honduras. Abstract translation by DavidTeichert-Coddington)

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