Population dynamics and size stratification in 75-day old bred juvenile African Catfish (Clarias gariepinus, Burchell, 1822) raised in concrete tanks
Cannibalism and aggressiveness exhibited more frequently by Catfish has been linked to disparity in sizes, sex ratio and/or stocking density, this study was carried out to investigate population dynamics and size stratification within the Clarias population bred in 4m x 4m x 1m artificial concrete tanks. A total of two hundred and fifty (250), 75-day old juveniles were randomly selected and measured for live body weight and linear body measurements which include, Total Length (TL), Standard Length (SL), Head length (HL), Pre-Dorsal Length (PDL), Dorsal Fin Length (DFL), Pre-Anal Length (PAL) and Anal Fin Length (AFL). Two indices (length-weight relationship and Fulton’s condition factors) were also computed for predictive assessment of future performances and wellbeing of the fish. The fish weight ranged between 3.30g and 20.30g with an overall mean body weight of 10.61 ± 0.28g. Based on the weight, the Sturge’s formula was used to construct nine class intervals of 2.0g width each, with the grouping resulting in disproportionate frequency distribution which was statistically (P<0.0001) significant. Of all the variables measured, weight had the highest variability within the population with a CV of 41.88%, while other measures had Coefficient of Variation of between 13.82% and 16.65%. It was observed that based on the mean body weight of the fish studied, only 6.4% are within the 95% Confidence Interval (CI) of the Mean, while 53.2% and 40.4% are respectively below and above the CI. This stratification and population structure provides a good discriminatory tool in separating the fish into fairly homogenous sizes for further rearing to minimize cannibalism and optimize profit.
Keywords: Catfish, Cannibalism, Measurements, Fish wellbeing