Effects of Water Temperature on Growth Performance and Health of Butter Catfish (Ompok bimaculatus)

Abstract

Increased water temperatures, decreased dissolved oxygen levels, and altered chemical substances in freshwater systems cause stress to fish and increase the likelihood of disease. These issues generate a significant amount of economic losses in aquaculture and clearly represent a normal impact of rapid water temperature changes on fish lives. This study examined growth performance and health conditions of butter catfish culture under elevated water temperature levels. In a 10-week experiment, 15 fingerlings per tank were cultured in 4 different temperature regimes (ambient temperature (25.1-29.5 °C) as the control, 29 °C, 31 °C, and 33 °C) with 4 replications. The initial average weight of the fingerlings was 2.72+0.01 g. Water quality parameters (dissolved oxygen (DO), pH, total ammonia nitrogen (TAN), and nitrite (NO2-N)) were measured weekly. Water pH, TAN, and NO2-N were not affected by water temperature, but from waste products in the tank. Except that DO slightly decreased when exposed to higher temperatures, with readings of 8.80, 8.79, 8.69, and 8.27 mg/l in the control, 29 °C, 31 °C, and 33 °C temperature regimes, respectively. Water pH (6.4-6.7) gradually decreased with no significant differences among treatments (p>0.05). TAN values in the control and 29 °C, 31 °C, and 33 °C treatments were 0.729, 0.805, 0.765 and 0.389 mg N/1, respectively. NO2-N values followed a similar pattern to TAN with the control treatment reaching the highest value (0.164 mg N/l) and the 33 °C treatment the lowest (0.103 mg N/l). However, all parameters were within safe levels for fish culture. The highest temperature (33 °C) negatively affected growth performance and fish health. The fish in this regime had significantly reduced percentages of weight gain, feed intake and specific growth rate (SGR) (479.70%, 194.28 g, and 2.55%/day, respectively). However, the feed conversion ratios (FCR) and survival rates did not differ by temperatures (p>0.05) and their values were positive for the culture. However, the fish immune systems were weakened with white blood cell counts (5.50x10 cells/ml) lower and lysozyme activity (8.30 μg/ml) higher in fish held at 33 °C. Even though the hemato-immunological parameters (serum protein, nitroblue tetrazolium (NBT) reduction, hematocrit, and average beads per cell) in all four treatments did not show any variations, other parameters (red blood cells, hemoglobin, and phagocytosis) had higher values, possibly a sign of compensation during the adaptation to their new regimes. Exposure to Edwardsiella ictaluri at a concentration of 1.32×10 CFU/ml led to a mild virulence which caused a 2.5% accumulated mortality rate in the fish held at 33 °C. This infection decreased with higher water temperatures, as there was a virulence rate of 100% accumulated mortality rate at ambient temperature. In summary, to accomplish good production in growth performance and maintain good fish health and water quality in a culture system, the optimal temperature range of butter catfish during the fingerling stage is between ambient temperature and 31 °C. However, fish farmers should take precautions during the culture because enteric septicemia of catfish (ESC), caused from E. ictaluri infection, is a potentially deadly problem in this thermal range. This study concludes that butter catfish can endure slightly increased temperatures arising from global warming.