Preliminary study on the natural extenders for artificial breeding of African catfish Clarias gariepinus (Burchell, 1822)

The objective of the present study was to determine the most suitable extender and their respective dilution ratios for African catfish sperm for artificial induced breeding and cryopreservation purposes. Three natural extenders were tested i.e. coconut water, sugarcane water and soybean solutions, at three different levels of sperm to extender dilutions of 1:20, 1:30 and 1:40. While Ringer solution was used as a control Diluted sperm were fertilized with ready isolated eggs to assess the fertility and hatching rate at 0, 6 and 12 hour intervals. The results showed that the eggs hatched approximately 19 to 27 hours after fertilization. In general, the fertilization and hatching rates decreased with increasing dilution ratio. With respect to natural extenders, the coconut water showed the highest fertility and hatching rates at 1:20 dilution ratio. Therefore, coconut water at 1:20 dilution ratio was the optimal condition for African catfish spermatozoa among the natural extenders investigated.

The effects of dieldrin on various life stages of the African catfish Clarias gariepinus (Burchell)

Early life stages (ELS) of Clarias gariepinus were found to be less sensitive to acute dieldrin toxicity than ELS of Nile tilapia, Oreochromis niloticus; 96 h LC50 for 37 day old fry were 11.7 and 4.95pg/l, respectively. Growth of O. niloticus fry was significantly reduced in 22.4 pg/l dieldrin whereas growth of C. gariepinus fry was unaffected. Adult C. gariepinus rapidly absorbed dieldrin from aquaeous solution and accumulated it in their tissues, especially in the liver where after 30 days in 4.0 pg/l bioconcentration was close to 1000 fold. Chronic exposure of C. gariepinus to dieldrin had no effect on blood haematocrit and haemoglobin, but appeared to slow the growth of catfish, and had a clear negative effect on the reproductive potential of mature females