Abstract
All possible hybridizations were done among Clarias batrachus, C. gariepinus and Heteropneustes fossilis. There were three successful viable hybrids such as cross magur (C. batrachus female x C. gariepinus male), local shigur (C. batrachus female x H. fossilis male) and African shigur (C. gariepinus female x H. fossilis male). However, reciprocal cross magur (C. gariepinus female x C. batrachus male) showed very low hatching rate of eggs (2.5%) and survival rate of larvae (0.5%); and all the fertilized eggs of reciprocal local shigur (H. fossilis female x C. batrachus male) and African shigur (H. fossilis female x C. gariepinus male) were found dead before hatching.Morphometric studies showed that cross magur and local shigur were closely related to their respective paternal parent. African shigur, on the otherhand, had developed intermediate characters to its parents. Male and female gonads of cross magur were well developed with normal eggs and milt production. But it was not possible to produce F₂ generation hybrids from cross magur, as all the fertilized eggs were found dead before hatching. Local shigur and African shigur were all male with no milt production. Reciprocal cross magur was also male and deformed. Experiments were done on hatching, larval development and survival of post larvae of parents and viable hybrids at temperatures maintained at 22°C, 25°C, 27°C, 29°C, 31°C, 33°C and 35°C. Hatching time showed an inverse relationship with temperature in all cases. The longest hatching time was recorded in C. batrachus and the shortest was observed in C. gariepinus at all temperatures. Cross magur and local shigur showed intermediate hatching time to their respective parents at all temperatures. African shigur showed long hatching time at lower temperatures (22--29°C) and short hatching time at high temperatures (31--35°C) in comparison to its parents.Hatching rate was highest at 27°C and 29°C and progressively less at increasing and decreasing temperatures in all cases. Cross magur showed the highest hatching rate among all the fishes studied. There was a 'critical period' in each temperature where a large number of eggs died. This critical period was found temperature - dependant and it took longer time to reach critical period in lower temperature and shorter time in higher temperature.Larval period had an inverse relationship with temperature in all cases. All the larvae of local shigur were found dead at all temperatures except 27°C and 29°C, at which, it showed the longest larval period. On the otherhand, C. gariepinus had the shortest larval period at all temperatures. The larval period of cross magur and African shigur were intermediate to that of their respective parents at all temperatures. The survival rate of larvae was highest at 27--29°C and progressively decreased towards increasing and decreasing temperatures. The highest survival rate of larvae was recorded in cross magur at all temperatures.The survival rate of post larvae (upto 21 days) was inversely related to time in all cases. It was recorded highest at 25°C, 27°C, and 29°C with progressive decrease at increasing and decreasing temperatures. Cross magur showed the highest survival rate at post larval stage during the experimental period.