Cause of cyclic variation in Honduran shrimp production

D.R. Teichert-Coddington, Department of Fisheries and Allied Aquacultures, and Alabama Agricultural Experiment Station, Auburn University, AL 38649 U.S.A.

R. Rodriguez, Granjas Marinas de San Bernardo, S.A., Choluteca, Honduras

W. Toyofuku, Aquacultivos de Honduras, S.A., Choluteca, Honduras

1 November 1994, CRSP Research Report 94-66

Abstract Relationships among stocking, harvest, and environmental variables for two commercial shrimp farms in southern Honduras were evaluated using stocking date as the time of reference. Data were analyzed from consecutive production cycles during 1986 to 1991 in Farm A and 1988 to 1991 in Farm B. Stocking ponds during March to June and November to February resulted in good and poor shrimp yields, respectively. Step-wise regression analyses revealed that survival, stocking density, salinity, and temperature accounted for up to 80% of the total variation in shrimp yield. The environmental variables alone could account for only a third of total variation. A similar analysis of a monthly means, which emphasized time related variation by minimizing inter-pond variability, revealed that temperature (75 to 85%) and percentage of stocked P. vannamei accounted for up to 88% of total monthly variation. Effects of salinity were minor. The majority of variation in shrimp yields within a farm was related to non-environmental factors whereas cyclical variation over a calendar year was primarily related to temperature and proportion of stocked P. vannamei. Climate cannot be controlled, but farm management can take its predictability into account.

This abstract was excerpted from the original paper, which was published in World Aquaculture 25:57-61, March 1994.

A variable growth rate modification of von Bertalanffy's equation for aquaculture

R.R. Springborn and A.L. Jensen, School of Natural Resources, University of Michigan, Ann Arbor, Michigan, USA

W.Y.B. Chang, Division of International Programs, National Science Foundation, Washington, DC, USA, and, Center for Great Lakes and Aquatic Sciences, The University of Michigan, Ann Arbor, Michigan, USA

1 December 1994, CRSP Research Report 94-67

Abstract In aquaculture experiments of only a few months' duration, fish can approach their asymptotic size and growth rates may change greatly. One objective of aquaculture is to obtain a maximum economic return, and a growth model is needed to relate rate of growth to food consumption and other costs to find the optimum duration of growth cycles. Von Bertalanffy's equation is an asymptotic growth model which can be used for this purpose. A variable growth rate model was developed to describe fish growth oscillations observed in aquaculture experiments. This growth model provides improved estimates of von Bertalanffy's equation in aquaculture and can be used for an efficient evaluation of fish production during production cycles.

This abstract was excerpted from the original paper, which was published in Aquaculture and Fisheries Management 25:259-267, 1994.

Effect of Nile tilapia (Oreochromis niloticus) on the ecosystem of aquaculture ponds, and its significance to the trophic cascade hypothesis

James S. Diana, Daniel J. Dettweiler, School of Natural Resources and , Center for Great Lakes and Aquatic Sciences, University of Michigan, Ann Arbor, Michigan 48109-1115, USA

C. Kwei Lin, Asian Institute of Technology, G.P.O. Box 2754, Bangkok 10501, Thailand

1 December 1994, CRSP Research Report 94-68

Abstract The trophic cascade hypothesis holds that an increase in fish biomass causes a decline in food organisms of the fish, which cascades down to regulate lower trophic levels by altered consumptive demands. This hypothesis was evaluated by stocking Nile tilapia (Oreochromis niloticus) at densities of 0, 1, 2, or 3 fish/m³ in triplicated 220-m³ ponds near Bangkok, Thailand. All ponds were fertilized with 500 kg chicken manure·ha^-1/wk^-1 (sic). We measured phosphorus, nitrogen, chlorophyll a, primary productivity, zooplankton abundance, and fish yield in all ponds. Increased stocking density resulted in decreased adult fish growth but similar yields among the three density treatments. Regressions relating the abundance of each trophic level to the next higher trophic level were either positive or nonsignificant, which is contrary to trophic cascade predictions. Zooplankton became significantly more dense over time in fishless ponds than the other three treatments, but no other trophic level differed among treatments. These results indicate that presence of fish had a significant effect on zooplankton in ponds, but biomass of fish or abundance of zooplankton did not significantly affect other trophic levels.

This abstract was excerpted from the original paper, which was published in Canadian Journal of Fisheries and Aquatic Sciences48:183-190, 1991.

Effects of urea application, aeration, and drying on total carbon concentrations in pond bottom soils

Mohammad Ayub, Claude E. Boyd, and David Teichert-Coddington, Department of Fisheries and Allied Aquacultures, Alabama Agricultural Experiment Station, Auburn University, Alabama 36849, USA

1 December 1994, CRSP Research Report 94-69

Abstract Aerated ponds did not accumulate as much carbon in bottom soils as control ponds. Application of urea to manured ponds did not accelerate carbon loss from bottom soils. When ponds were drained for fish harvest, appreciable carbon was eroded from the surface layers of bottom soil. Further decomposition of soil carbon occurred during the 5-week drying period between crops. Within-pond variation in soil carbon concentration was high; a technique for selecting replication and sample size requirements for experiments on changes in bottom soil carbon concentration is provided.

This abstract was excerpted from the original paper, which was published in The Progressive Fish-Culturist 55:210-213, 1993.

Pond bottom soil respiration during fallow and culture periods in heavily-fertilized tropical fish ponds

Claude E. Boyd, and David Teichert-Coddington , Department of Fisheries and Allied Aquacultures, Alabama Agricultural Experiment Station, Auburn University, Alabama 36849 USA

1 December 1994, CRSP Research Report 94-70

Abstract Benthic respiration in two fish culture ponds at Comayagua, Honduras, was below 1 g CO₂/m² per day during culture periods. When ponds were drained for fish harvest, bottom soils were exposed to the air, and soil respiration rates as high as 10 g CO₂/m² per day were recorded. High rates of soil respiration following removal of saturated conditions declined as labile organic matter was consumed and soil moisture content declined. Laboratory studies showed that the moisture content for greatest soil respiration was near saturation, and either drying soils or completely saturating them drastically reduced respiration. Although soil respiration rates were much greater during the fallow period than during the culture period, more organic matter was decomposed during the culture period because it was much longer (5 months) than the fallow periods (2 weeks).

This abstract was excerpted from the original paper, which was published in Journal of the World Aquaculture Society 25:417-423, 1994.