Phosphorus fertilization strategy in fish ponds based on sediment phosphorus saturation level

Madhav K. Shrestha and C. Kwei Lin, School of Environment, Resources and Development, Asian Institute of Technology, GPO Box 2754, Bangkok 10501, Thailand

21 January 1997, CRSP Research Report 97-101

Abstract Two experiments were conducted to determine effective P fertilization strategy in fish ponds in relation to sediment P saturation level. Experiment 1 was conducted in cement tanks with five levels of P saturation in the sediments (5, 24, 44, 60, 79%) and with three P fertilization rates (0.2, 0.1 and 0.05 g m^-3 day^-1, N:P ratios of 2:1, 4:1 and 8:1, respectively). Nile tilapia (Oreochromis niloticus) were cultured in the tanks for 57 days. Results showed that the mean concentration of soluble reactive phosphorus (SRP) in the water column increased with increasing sediment P saturation and P fertilization rate. The maximum net fish yield (NFY), 4.2 ± 0.3 g m^-3 day^-1, was obtained at an SRP concentration of 0.3 mg l^-1; higher concentrations did not increase fish yield. These levels of SRP and NFY were attainable with P fertilization rates of 0.2 g m^-3 day^-1, 0.1 g m^-3 day^-1 and 0.05 g m^-3 day^-1 and N:P ratios of 2:1, 4:1, and 8:1 in ponds where the level of sediment P saturation was below 10%, above 45% and above 60%, respectively. Experiment 2 was conducted in earthen ponds to test and verify the P fertilization rate based on the cement tank results. Three new and three old ponds with 8 ± 1.7% and 88 ± 7.3% sediment P saturated in the top 5 cm of mud were fertilized at a rate of 0.2 g m^-3 day^-1 and 0.05 g m^-3 day^-1 and N:P ratio of 2:1 and 8:1, respectively. Nile tilapia were cultured at a density of two fish m^-3 for 85 days. The mean NFY obtained in new and old ponds were 1.73 ± 0.08 g m^-3 day^-1 and 2.24 ± 0.32 g m^-3 day^-1, respectively, which were not significantly different (P>0.05). We conclude that P fertilization rate should be based on P saturation level in mud to overcome the problem of under or over supply of P in fish ponds.

This abstract was excerpted from the original paper, which was published in Aquaculture, 142(1996):207-219

Polyculture of tilapia with marine shrimp

Bartholomew W. Green, Department of Fisheries and Allied Aquacultures, Auburn University, Al 36849-5419

21 January 1997, CRSP Research Report 97-102

Abstract The potential for tilapia-marine shrimp polyculture is evaluated. Aquaculturally important tilapia are the Nile tilapia (Oreochromis niloticus), blue tilapia (O. aureus), red tilapia (Oreochromis spp.) and, to a lesser extent, Mozambique tilapia (O. mossambicus). Nile and blue tilapia can tolerate salinities as high as 36 ppt to 40 ppt, but best growth occurs at salinities below 20 ppt. Red tilapia, either from Florida or Taiwan, survive and grow well in salinities of 36 ppt. Mozambique tilapia is able to tolerate salinities as high as 120 ppt, but good growth is reported through salinities of 36 ppt. While these tilapia can spawn in waters of various salinities, greater fingerling production is achieved in freshwater or slightly saline (2 ppt to 5 ppt) waters. Maximum salinity tolerance in tilapia appears to be reached at a total length of 50 to 70 mm. Acclimation of tilapia from freshwater to saline water is best accomplished by increasing salinity from 2.5 ppt to 5 ppt daily until the desired salinity is reached. Season, choice of culture species, market, and management/logistical considerations of tilapia-marine shrimp polyculture are discussed. Polyculture of tilapia and marine shrimp may be limited to 6 to 7 months each year during and immediately following the rainy season along the Pacific Coast of Central America depending on the tilapia species selected for culture. Tilapia can be stocked directly into ponds or into cages placed in ponds, supply canals or drain canals. It remains necessary to determine the optimum stocking rates of tilapia for polyculture with marine shrimp and to validate these production systems on commercial farms.

This abstract was excerpted from the original paper, which was published in Actas del Primer Simposio Centroamerica sobre cultivo de tilapia, 1995;177-127.

Timing of supplemental feeding for tilapia production

James S. Diana, School of Natural Resources, University of Michigan, Dana Bldg, 430 E Univ, Ann Arbor, MI 48109-1115 USA

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

14 April 1997, CRSP Research Report 97-103

Abstract The staged addition of feed to fertilized fish ponds was evaluated by adding fertilizers to 15 ponds stocked with Nile tilapia Oreochromis niloticus, then adding feed at half ad libitum rates once fish in the ponds reached a target weight. Each pond was stocked with 750 fish (3 fish/m²), and each treatment included three ponds with first feeding at (a) 50 g, (b) 100 g, (c) 150 g, (d) 200 g, and (e) 250 g. Ponds in Thailand (at the Ayutthaya Freshwater Fisheries Station, Royal Thai Department of Fisheries) were maintained for 236-328 d until the fish reached 500 g.

Growth was similar for all treatments under fertilizer alone (1.17 g/d) and was also similar when feed was applied (3.1 g/d). Feed application rates averaged 1.17% BW/d, indicating substantial use of natural food. Pond water quality did not deteriorate under supplemental feeding. Feed conversion rates averaged 1.03. Multiple regression indicated that 73.8% of the variance in growth was explained by design variables (feed input and days), while 86.2% of the variance in growth was explained by adding dissolved oxygen content and alkalinity into the equation.

The most efficient system was to grow fish to 100-150 g with fertilizers alone, then add feed. First adding feed (at 50% ad libitum) once fish reached 100 g produced the highest predicted annual revenues ($6,164 per hectare). Results of this experiment indicated that either critical standing crop occurred early (before the first fish sample) or did not occur at all in these ponds.

This abstract was excerpted from the original paper, which was published in the Journal of the World Aquaculture Society, 27(4)1996:410.

Optimal resource allocation by fish farmers in Rwanda

Carole R. Engle, Ph.D. Department of Aquaculture and Fisheries, University of Arkansas at Pine Bluff, 1200 North Univ Drive, Box 4912, Pine Bluff, AR 71611

14 April 1997, CRSP Research Report 97-104

Abstract Although many small-scale fish farming projects around the world promote fish production as a source of low-cost protein, increasing evidence demonstrates fish to be an important cash crop, even for limited-resource farmers. A mathematical programming model was developed from survey data of Rwandan farmers to determine optimal resource allocation on subsistence farms in Rwanda. The specific objective of the study was to determine farm plans that maximize returns to a representative Rwandan farm family's resources, subject to constraints of the farm family's proteinic and caloric requirements. Soybeans, sweet potatoes, and maize were selected to meet household nutritional requirements. Fish production was selected as the principal cash crop, in most cases lending support to the evidence that fish is more important as a cash crop than as a primary protein source in Rwanda

This abstract was excerpted from the original paper, which was published in the Journal of Applied Aquaculture, 7(1)1997:1-17.

Observations and model predictions of daily areal primary production in a eutrophic brackish water culture pond

James P. Szyper, Hawaii Institute of Marine Biology, School of Ocean and Earth Science and Technology, University of Hawaii at Manoa, P.O. Box 1346, Kaneohe, HI 96744, USA

16 April 1997, CRSP Research Report 97-105

Abstract Observations of daily gross primary production of oxygen per unit area in a eutrophic, brackish water shrimp culture pond over a 14-day period are compared with predictions from two models in order to assess the utility of the model approaches for ponds and to refine observational protocols and techniques for pond assessment.

The models predicted rates (3.2 to 37.7 g O₂ m^-2 d^-1) which exceeded observations (4.7 to 15.7 g O₂ m-2 d-1) at all but the lowest light levels. Observed rates were also lower than other observations at similar light levels. These shortfalls are attributed to (1) the inadequacy of the method for estimation of community respiration as a component of gross production, in the absence of direct observation; and (2) the possibility of nutrient limitation of rates in the pond ecosystem.

The models are sufficiently sensitive to chosen parameter values, and the day-to-day variation of the parameters in the ecosystem likely sufficiently variable, that daily determinations of parameters should be made when possible, with particular attention to timing and use of surface water. Field observations of daytime community respiration, and improved knowledge of its controlling factors and relationships, are important needs for the advancement of model treatment of photosynthesis in ponds.

Eutrophic pond ecosystems have characteristics (vertical temperature structure resembling natural water bodies, complete light extinction within the shallow water column) which make them amenable to study as microcosms of some general aspects of aquatic primary production, particularly problems involving the prediction of daily areal rates from small-scale volume-based rate data.

This abstract was excerpted from the original paper, which was published in the Ecological Modelling International Journal on Ecological Modelling and Systems Ecology, 88(1996):83-92.