Effects of storage and incubation
temperature on the viability of eggs, embryos and larvae in two strains of
an African catfish, Heterobranchus longifilis (Siluriformes,
Clariidae)
D. Nguenga,
G.G. Teugels, M. Legendre, F. Ollevier-2004
Aquaculture Research, 35(14): 1358-1369
Abstract:
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 (3-5°C) and at ambient room temperature
(20.5-22°C). In the second experiment, eggs were incubated from
fertilization to hatching at different experimental temperatures (21, 25,
29, 32 and 35°C) 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 3-5°C
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 29°C,
respectively, for NS and LS. The length of the hatching period was
remarkably shorter for LS than NS at any tested incubation temperature,
except 35°C. No hatching took place at 21°C. The highest proportion of
normal larvae occurred at 25 and 29°C, respectively, for NS and LS.
Hatching rate was highest at 25 and 29°C, respectively, for NS and LS.
There was a significantly higher proportion of deformed larvae at 35°C
regardless of the strain.
(IRAD, Fishculture & Fisheries Research Unit, PO Box 255,
Foumban, Cameroon. E-mail: nguengadavid@yahoo.fr)