Improving on-farm hatchability of Clarias gariepinus eggs by narrowing the range of incubation temperature
In order to facilitate the reproduction of African catfish Clarias gariepinus by smallholders who cannot afford hatchery buildings, electricity and pipe-borne water, the hatchability of fertilised eggs was assessed under the conditions of a dry and a rainy season, as well as under artificial conditions to protect incubating eggs from wide temperature variability. This comprised incubation in small vs. in large water volumes, in covered vs. in exposed vessels, at surface vs. at bottom of vessels and in brightly coloured vs. in black vessels. During the dull rainy days, temperature
ranged from 24 to 27°C in hapas (implanted in a 200,000 L pond) and from 24 - 30°C in 30 L plastic tanks, regardless of covering or depth of measurement. During the bright sunny days, water temperature varied from 23 - 30 °C in the hapas and from 19 – 37 °C in the plastic tanks. Covering with white locally available polythene bags, enabled the narrowing of temperature range in tanks but not in hapas (ponds). Tank colour did not significantly affect the water temperature. Temperature ranges were narrower at bottoms than at surfaces in hapas but not in tanks. Egg hatchability was inversely proportional to temperature range: the narrowest range conferred a hatchability of 57.21 % while the widest range completely inhibited it. These results were used as bases for recommending best practices for on-farm incubation of C. gariepinus eggs.
Key words: Smallholders, On-farm incubation, improved hatchability