Effect of size hierarchy on growth and surfacing behaviour in Betta splendens

Abstract

Effect of size hierarchy on food conversion rate and surfacing behaviour in relation to density and feeding frequency were studied in B. splendens. When three size groups of B. splendens were reared individually, small fish consumed the more quantum of feed and also exhibited the higher conversion rate than the other two size groups. The conversion rate of B. splendens was gradually decreased with increasing the body size when they reared individually and grouped together. A significant (P < 0.05) and negative correlation was obtained between the SGR in terms of length / weight gain and body size groups in B. splendens reared under both isolated and grouped. Similar trend was also obtained in surfacing frequency and distance travelled. The feeding frequency significantly (P < 0.05) influenced growth, surface frequency and distance travelled in chosen size groups of B. splendens in relation to density. In low density groups (4 – 8 fish tank-1), fish receiving two meals a day grew better than other size groups while in high density groups, three meals a day elicited the maximum growth than other size groups. Statistically significant (P < 0.05) coefficients were obtained for the relation between conversion rate and density in all tested feeding frequencies. Among the feeding schedules, 2/1 Ff elicited the maximum performance on conversion rate in larger fish than smaller fish. The slope value obtained for conversion rate of larger fish was 2.25 and it declined to 1.36 in smaller fish and both were received two meals a day. It indicates that in all densities, the larger individual converted at a faster rate than the smaller one. Based on the slope value of conversion rate, the smaller individual could grow only about 60% of the larger individual.