Hybridization of Clarias gariepinus and Heterobranchus bidosarlis with observation of polygenic inheritance and survival of the hatchlings in three different levels of borehole water
Hybridization of two strains of Clariids (H. bidosarlis and C. gariepinus) and rearing of the hatchlings in borehole water at three different water depth (5 cm', 10 cm' and 15 cm') in glass aquaria for eight weeks was carried oufin indoor hatchery of the Department of Water Resources, Aquaculture and Fisheries, Federal University of Technology Minna. The experiment was carried out to observe and to compare the inheritance of external features of the hybrid Heteroclarias and normal Clarias gariepinus and Heterobrachus bidosarlis and also to test their survival in borehole water at three different water depth. The hatchlings were fed adlibitum with live Daplmia and Moina zooplanktons. Results of the survival and mortality rates in different water levels were compared by ANOV A. Treatment 1 (5 cm3 water depth) had survival rate of 46.25 % and mortality of53.25%. Treatment2 (10 cm3 water depth) had 54.25% survival and45.75% mortality. Treatment 3 (15 cm3 water depth) had 74.75% survival and 25.25% mortality. Although the survival rate increased as the water depth increased, the differences were not significantly different (P > 0.05). On the inheritance of some morphological features, the hybrid Heteroclarias was observed to have small adipose fin compared to the normal large adipose fin of Heterobranchus bidosarlis and absence of adipose fin in Clarias gariepinus. The hybrid also had shorter head length (less than 1 /3 of total body length) and a bigger barbel size (about 2mm thick) than normal C. gariepinus which have longer head length (about 1/3 of total body length) and slender barbels (about lmm thick). These were observed to be the dominant characters of H. bidosarlis over C. gariepinus. The hybrid frys grew normally. The regression equations of the lengthweight relationships were Y = -6.34 + 3. 52x, r1 = 0.96 for Heteroclarias (hybrid). The mean initial and final total body length and weight after eight weeks for the hybrids were; 8 mm initial length and 59 mm final length, 0 .14 mg initial weight and 0.57 mg final weight. Specific growth rate (SGR) for the hybrid was 4.35 mg. The mean water quality parameters during the hybrid rearing experiment were; temperature 26°C, pH 6.5, dissolved oxygen (DO) 7 .5 mgL1 and conductivity 0.29 ohms/mis.
KEY WORDS: Hybridization, Heteroclarias, water depth, survival rate and mortality rate.