Factors Affecting Variation in Growth of Channel Catfish Fingerlings and Mathematical Modelling of Their Population Statistics

Abstract

A partial differential equation was used to predict population structures in channel catfish, Ictalurus punctatus, fingerlings stocked at low (150,000/ha), medium (300,000/ha), or high (600,000/ha) densities in earthen ponds. An exponential growth rate function incorporated into the model gave better prediction than a constant mean growth rate at low and medium densities. However, both expressions of the growth rate could be used at high fish density without affecting the solutions of the model. Mortality did not have substantial effect on the solutions of the model at either of the three densities. A partial differential equation was used to predict population structures in channel catfish, Ictalurus punctatus, fingerlings stocked at low (150,000/ha), medium (300,000/ha), or high (600,000/ha) densities in earthen ponds. An exponential growth rate function incorporated into the model gave better prediction than a constant mean growth rate at low and medium densities. However, both expressions of the growth rate could be used at high fish density without affecting the solutions of the model. Mortality did not have substantial effect on the solutions of the model at either of the three densities. The components of the total variance in size in channel catfish fingerlings were also determined using populations cultured in tanks. After a 90 day culture period, 86% of the total variance for length and 65% of the total variance in weight could be explained by conditions of the environment. A variance model was used to described the rate of increase in the coefficient of variation {CV). Initial stocking density and time had substantial impact on the rate of increase in the CV. However, fish size did not account for the increase in CV over time. The variance model suggested an asymptotic CV for each population, a value of which was a function of the environment in which the fingerlings where cultured. Mortality was predicted using variations of the length­based method. The traditional method underestimated mortality rates. However, using the descending limb above the modal length improved the prediction of mortality. Growth rate of channel catifsh fingerlings was related to feeding levels and stocking density. In 1992, growth rate was similar at 150,000/ha and 300,000/ha, but greatly reduced at 600,000/ha. Increasing the stocking density from 100,000 to 300,000/ha resulted in 50% more fish harvested and a yield of 2,745 kg/ha rather than 1,809 kg/ha. However, increasing the density from 300,000 to 600,000/ha resulted in only 9% higher fish harvest and lower yield (1,213 kg/ha). Partial harvest increased yield and mean size but not survival.