Allometric indices of Chromidotilapia guentheri (Sauvage 1882), Tilapia mariae (Boulenger 1899) and Tilapia zillii (Gervais 1848) of the Osse River, Southern Nigeria

Three cichlids, Chromidotilopia guentheri, Tilapia mariae and T. zilli were collected from the Osse River at Ikoro and examined for length frequency distribution and length weight relationships (LWR). The mean length and weight were 11.05±0.35cm and 51.75±5.63g for Chromidotilapia guentheri, 13.57±0.54cm and 124.67±17.54g for T. mariae and 17.45±0.69cm and 232.92±28.01g for T. zilli. The length frequency distributions for C. guentheri presented a slightly positively skewed distribution with modal length being 10.0 - 10.9cm size class. T. mariae had a positively skewed distribution with a modal size class of 11.0 – 12.9cm. The frequency distribution was bimodal for T. zilli, with modal size classes of 13.0 – 14.9cm and 19.0 – 20.9cm. The regression coefficient (b) was used as an allometric growth index showing a positive regression of weight on length for the three species. The regression coefficients of 1.169, 1.577 and 2.706 for Chromidotilopia guentheri, Tilapia mariae and T. zilli respectively were tested for significance using the Single Factor Analysis of Variance (ANOVA). Chromidotilapia guentheri indicated no significant regression of weight on length (P > 0.05); T. mariae was significant (P < 0.05), while T. zilli was highly significant (P < 0.01), showing the highest degree of isometric growth.