Effects of rearing temperature on egg incubation, growth, standard metabolic rate, and thermal tolerance of chocolate mahseer, Neolissochilus hexagonolepis.

Abstract

The present study was aimed to assess the effect of temperatures on egg incubation, growth, standard metabolic rate (SMR), and thermal tolerance of a near threatened Himalayan hill stream chocolate mahseer (Neolissochilus hexagonolepis). For the hatching study, eggs were incubated in four temperatures (17, 20, 23, and 26 ◦C). The total hatching and free-swimming larvae percentage were higher at 23 ◦C (p < 0.05). Experiment I (for validation of the CTmax method) was carried out by incubating eggs at 17 ◦C and 23 ◦C. The CTmax was estimated in response to different warming rates (1–18◦C h 1), acclimation temperatures (17 and 23◦C), and the age of fishes (8, 15, 35 dph). The results suggested that a warming rate of 18◦C h 1 could be used for the thermal tolerance study of yolk-sac larvae (8 dph) and 35 dph larvae, but for free-swimming larvae (15 dph) up to 3◦C h 1 is suitable. Experiment II (for growth, SMR and thermal tolerance) was carried by acclimatizing 15 dph larvae in five temperatures (15, 19, 23, 27, and 31 ◦C) for 60 days. The mean growth rate increased with the increase in temperature from 15◦C to 27◦C (1.30–3.58% day 1) and decreased at 31◦C. The mean SMR of the chocolate mahseer in the above acclimation temperatures was ranged from 1.14 ± 0.36 to 2.81 ± 0.15 μgO2h 1mg 1 and were significantly different (p < 0.01). The Q10 with the SMR of the fish suggested the preferred temperature ranged between 23 and 27 ◦C, and the optimum temperature for growth (ToptG) was estimated to be 25 ◦C. Chocolate mahseer is an eurythermal species which is advantageous for aquaculture practices due to its wide thermal tolerance zone (411.68◦C2 in 15 to 31 ◦C acclimation temperature range) and high ARR values (0.49 - 0.54).