Intake and discharge from six shrimp farms located on riverine or
embayment estuaries of the Gulf of Fonseca were sampled during rainy and dry
seasons of 1993 to 1994. There was a mean net consumption of inorganic nitrogen
and phosphorus, and a mean net discharge of organic matter. Discharged material
was greater in embayment estuaries. Use of inorganic fertilizers promoted
discharge of phosphorus and nitrogen. Total settleable solids and most
nutrients were greater at the end than at the beginning of pond draining. An
exception was BOD, which did not change during the course of pond draining. The
majority of nitrogen entered and left ponds by water exchange. Most phosphorus
entered ponds with feed, but left ponds by water exchange. Mean conversion
ratios of feed nitrogen to shrimp flesh ranged from 1.4 to 4.1. Mean phosphorus
conversion ratio was 6.3. Pond discharge of both nitrogen and phosphorus
increased linearly with the feed conversion ratio. Nitrogen conversion ratios
were not different for embayment or riverine estuaries. However, the conversion
of feed and nitrogen to shrimp flesh was greater during the wet than the dry
Relationships among stocking density, survival, and yield were evaluated
in ponds affected by the Taura Syndrome during wet and dry seasons in Honduras.
Ponds were stocked with juvenile Penaeus vannamei at 6, 8, 10, or 12/m
2. The design was tested on two farms during the wet season and on three farms
during the dry season. There was no significant correlation between shrimp
stocking density and survival during either season. Season did not affect
survival. Production increased with density during both seasons. Net income
increased with density during the wet season, but decreased or remained neutral
with an increase in density during the dry season. Net income was related to
both production and individual shrimp weight. Mean shrimp weight did not
decrease predictively with stocking density. Management strategies for ponds
affected by Taura are discussed.
Effects of nitrogen fertilization on water quality and tilapia yields in
earthen fish ponds supplied with adequate levels of phosphorus was tested.
Ponds were stocked with tilapia at a density of 2/m 2. Nitrogen was supplied as
urea at 0, 7, 14, or
28 kg/ha-wk. Primary productivity responded positively to nitrogen
Chlorophyll a increased linearly (P <0.01), and Secchi disk
visibility decreased curvilinearly (P <0.05) with increasing rate
of fertilization. However, fish yields were not significantly correlated with
nitrogen input, despite higher phytoplankton biomass. Cool dry season water
temperatures apparently inhibited fish growth. Fish were unable to take
advantage of higher available nutrient supply.
Previous studies demonstrated that shrimp production is similar at
protein levels between
20% and 40%, when shrimp are stocked at densities between 5 and 11/m2. Feeding
rates in these studies were such that feed efficiency was relatively low.
Another trial conducted in Choluteca with shrimp stocked at 7.5/m2
demonstrated that production during the dry season was not significantly
affected by a 50% reduction in feeding rate. Wet season production was impacted
significantly by the
50% reduction in feeding, but feed efficiency was improved. These results
indicated that too much feed was applied during the dry season, and that wet
season feeding rates might be reduced, but not by half. It is possible that a
comparatively high protein diet might improve shrimp growth and feed
conversion, if used at a feeding rate that is low compared with that employed
with lower protein diets while reducing nitrogen levels in pond effluents. Pond
chemical budget studies indicate that nitrogen discharge increases with both
feeding rate and diet protein level. Primary productivity in estuaries appears
to be limited by nitrogen. It is therefore economically and ecologically
important to feed at appropriate rates with an appropriate protein level.
The objective of this research is to test the effect of diet protein level on food conversion and nitrogen effluents during the production of Penaeus vannamei at semi-intensive stocking levels during the warm (wet) season and cool (dry) season. The null hypotheses to be tested are: 1) Shrimp growth, yield, and feed conversion during each season will be independent of feeding rate and dietary protein level, and 2) Nitrogen discharge from shrimp ponds during each season will be independent of shrimp feeding rate and dietary protein level.
A completely randomized design in 2x2 factorial arrangement was used to test two feeding rates (50% and 75% of feeding curve) each at two levels of protein (20% and 30% protein); each treatment was replicated three times. Penaeus vannamei post-larvae (PL 8-10) were stocked at 25/m (250,000/ha) in earthen ponds (0.7-1.0 ha) on 10 August 1995. A survival rate of 30% was assumed because of Taura Syndrome-induced mortality. Inlet and outlet water samples were collected for analyses of water quality variables. The experiment is scheduled to be harvested in December 1995.