Interspecific variation in tolerance of tilapia yolk sac fry (Family: Cichlidae) to copper stress
P P G S N SIRIWARDENA, K J RANA and D J BAIRD
Tolerance to pollutant stress could be related to modes of life of species. Although differences in mode of life may or may not be brought about by stress, such differences could be adaptive in terms of pollutant resistance. In the present study, the tilapia yolk sac fry were exposed to acute copper stress in order to determine whether there is a general tolerance response among faster developing substrate spawning and slower growing mouth brooding tilapia yolk sac fry. To predict the possible underlying mechanism to withstand metal stress, early life history growth traits, such as specific growth rate and yolk utilizing efficiency were measured in tilapia yolk sac fry under non-stress conditions. The six tilapia species used in this study were Oreochromis niloticus, Oreochromis mossambicus Oreochromis aureus as mouth brooding species and Sarotherodon galilaeus, Tilapia rendalli and Tilapia zilli as substrate spawning species.
There was a significant (p<0.05) inter-specific variation in the response to acute copper stress among the species tested. The yolk sac fry of mouth brooding species were consistently more sensitive than those of the substrate spawning species. The inter-specific variation in mean specific growth rate (df = 5.12: F = 999.99: p<0 05) and yolk utilizing efficiency for the period from hatching to maximum body weight attainment (df = 5.12: F = 21.196: p<0 05) were significantly different.
The response and the rank order of tolerance to copper between the six species tested reflect a difference in general stress response between the two groups of substrate and mouth brooding tilapia, which may be related to differences in modes of life.