Aquaculture research vol:35 issue:14 pages:1358-1369
Two experiments, dealing with short-term storage of ova and thermal conditions to optimize gamete and eggs management in hatcheries of the African catfish, Heterobranchus longifilis, were carried out. In the first experiment, ova collected by stripping from two strains of H. longifilis were stored for intervals up to 8 h at two temperature regimes: in a domestic refrigerator (3-5degreesC) and at ambient room temperature (20.5-22degreesC). In the second experiment, eggs were incubated from fertilization to hatching at different experimental temperatures (21, 25, 29, 32 and 35degreesC) to determine the effects of temperature on the kinetics of white egg appearance, hatching times and hatching quality. Gamete storage at warmer temperatures significantly prolonged viability irrespective of the strain used. In fact, the hatching rate for ova stored at 20.5-22 and 3-5degreesC for 5 h ranged between 75.2-79.3% and 6.5-9.4% respectively. Loss of viability was most noticeable after 6 h storage at ambient room temperature. Post-storage viability significantly declined after 2 h exposure to the domestic refrigerator temperature. No hatching of normal larvae took place after 8 h post-storage time. Results from the second experiment showed that time to maximum whitening of eggs was both strain- and temperature-dependent. The time to maximum mortality of eggs was shorter in the Layo strain (LS) than in the Noun strain (NS), regardless of incubation temperature. The appearance of white eggs was shorter with increasing incubation temperatures. Hatching times decreased with increasing temperature, regardless of strain. Hatching took place from 21 to 27 h and 19 to 24 h after fertilization at temperature of 29degreesC, respectively, for NS and LS. The length of the hatching period was remarkably shorter for LS than NS at any tested incubation temperature, except 35degreesC. No hatching took place at 21degreesC. The highest proportion of normal larvae occurred at 25 and 29degreesC, respectively, for NS and LS. Hatching rate was highest at 25 and 29degreesC, respectively, for NS and LS. There was a significantly higher proportion of deformed larvae at 35degreesC regardless of the strain.