Biology and culture of the clown loachChromobotia macracanthus(Cypriniformes, Cobitidae) : 4- Thermal biology of embryos and larvae

Abstract

The knowledge of how fish survive and grow at different temperatures, and how these traits vary between life stages, is essential to evaluate the effects of climate change on wild fish and implement effective strategies in aqua- culture. These issues are addressed in this study through a series of experiments that evaluate the effect of temperature (23−34 ◦ C) on the embryos and larvae of clown loach, Chromobotia macracanthus. This species is endemic to the rivers of Sumatra and Borneo, highly praised on the ornamental fish market, and has been reproduced in captivity recently. No embryo survived a 24-h exposure to 34 ◦ C until the age of 3 days after hatching (dah); mortality was high at 32 ◦ C at 2 and 3 dah, whereas it was low and similar from 1 to 4 dah at 23−29 ◦ C( <10%). Yolk absorption was proportional to water temperature (Q10 ◦C of 1.69 in the 23−32 ◦ C range), but fish reared at cold temperatures were larger than others at the start of exogenous feeding (5.7 vs. 5.5 mm TL, at 23 and 32 ◦ C, respectively). The survival of larvae fed Artemia nauplii ad libitum was high at 23−32 ◦ C( 80 −100%), but almost null at 34 ◦ C. Growth models at different tempera- tures were produced from weekly measurements in two experiments, and tested by comparing their predictions with the results of a third experiment. Throughout the larval stage, the optimal temperature for growth (T ◦) was close to 29 ◦ C, and departures from T ◦ resulted in substantial growth penalties (−30% SGR for -5.1 ◦ Ca nd+3.1 ◦ C). High survival, fast growth (0.7 mm day −1 ) and limited size dispersal at T ◦ opt are encouraging perspectives for the aquaculture of clown loach. From an ecological perspective, the species has an atypical thermal biology, as it is less thermophilic than other tropical fishes, but more stenothermal than temperate fishes exhibiting similar values of T ◦ opt, both traits being of particular concern in the context of global warming.