Effect Of Grow-Apart Syndrome On The Head Diameter, Body Length And Cannibalism In Clarias Gariepinus (Burchell, 1822) Hatchlings
Nine indoor rectangular (0.53 m3) concrete tanks were each stocked with induced-bred Clarias gariepinus fry (mean ± standard error of mean (s.e.m.) =1.63±0.61g) at 500 fry per tank. Ad libitum feeding, restricted feeding and no-feeding treatments each of mixed zooplankton and hatched brine shrimp (Artemia salina) replicated three times was used. One hundred and fifty fry each weighing 2.22 ± 1.22 g (mean ± s.e.m) from the indoor rearing exercise were stocked in each of nine 150 m3-capacity outdoor earthen ponds. These were similarly replicated and treated as in the indoor tanks but 40% crude protein crumbled artificial feed was used. The increase in body length, head diameter and the frequency of cannibalism in the fry were monitored indoor and outdoor for 14 days. The results showed that fish reared in the outdoor earthen ponds had better increases in standard lengths (SL) and total lengths (TL) than those reared in indoor tanks. There were significant differences (P < 0.05) in mean increases in the TL and SL per day for the jumpers (JP) whether reared indoor or outdoor. On the contrary, no significant differences (P > 0.05) in increases in SL and TL per day were recorded for the non-jumpers (NJP) whether reared indoor or outdoor. Fish fed ad libitum showed better increases in length and head diameter for both the jumpers and the non-jumpers than those on other feeding regimes. Unlike in outdoor rearing, increase in the head diameter of the JP and the NJP raised on different feed regimes was significantly different (P < 0.05) for indoor hatchery. The 36.75% mortality obtained in indoor hatchery was due mainly to cannibalism. Little or no feeding of C. gariepinus fry therefore enhanced grow-apart syndrome which encouraged cannibalism, differences in body length and head diameter.
Keywords: jumpers, non-jumpers, restricted feeding, ad libitum, mortality, cannibalism.
IFE Journal of Science Vol. 9 (1) 2007 pp. 33-44