The influence of environmental factors on fish production in tropical ponds investigated with multiple regression and path analyses

Abstract

1. A data set from integrated animal-fish farming experiments comprising 63 variables with nearly 45000 data points was analysed for interrelationships in the system and for causal effects on fish growth. 2. A new multivariate method for the analysis of multifactor data on the basis of multiple regression resulted in the identification of five major environmental variables governing fish growth in the present system: water temperature, wind, BOD of the added manure, pond size, and early morning oxygen content of the pond water. 3. It was found that the early morning oxygen content is mainly a measure of plankton standing crop and therefore represents the nutritional status of the pond for the cultured fish. This explains the negative sign of the regression coefficient for oxygen content. All other environmental variables showed positive effects on fish growth. 4. The new method permitted to derive parameters of the von Bertalanffy growth function for Nile tilapias. The obtained value for K is 5.409, indicating rapid growth of the fish. The values for Loo range from 15.8 to 23.9 cm depending on environmental conditions. 5. One of the advantages of the new method is the possibility to predict fish growth with good accuracy over the whole experimental period, simultaneously taking into account the environmental changes affecting fish growth. The level of precision in growth prediction is mainly affected by the quality of the fish-size data used in deriving the model. 6. The method of path analysis was successfully introduced to aquaculture for the interpretation of experiments and proved valuable to unravel interrelationships in the system