Dissolved-Oxygen Requirements of Three Species of Fish

Critical dissolved-oxygen levels and standard metabolic rates were determined for the bluegill, Lepomis macrochirus; largemouth bass, Micropterus salmoides; and the channel catfish, Ictalurus punctatus, at 25° C., 30° C., and 35° C. Two types of experiments were conducted: shock tests in which the dissolved oxygen was dropped rapidly from near saturation to a critically low point; and acclimation tests in which the dissolved oxygen was lowered gradually over a longer period of time. The minimal dissolved oxygen survived by fish in acclimation tests was lower than that survived in shock tests at any given temperature. In shock tests the minimum dissolved oxygen survived by bluegills was 0.75 p.p.m. at 25° C., 1.00 p.p.m. at 30° C., and 1.23 p.p.m. at 35° C. Slightly higher values were obtained for the largemouth bass at all three temperatures and for the channel catfish at 25° C. and 30° C. At 35° C. the channel catfish was more tolerant of low dissolved oxygen than either the bluegill or largemouth bass. In the acclimation tests the critical oxygen values obtained for bluegills were 0.70 p.p.m. at 25° C., 0.80 p.p.m. at 30° C., and 0.90 p.p.m. at 35° C. With the exception of the channel catfish at 35° C. slightly higher values were obtained with the largemouth bass and channel catfish. Within each species there was little difference between standard metabolic rates at the three temperatures. The standard metabolic rate of the bluegill at 25° C. was lower than that of the other species at the same temperature. Bluegills and largemouth bass weighing more than 15 grams showed no change in metabolic rate with increasing size, but below this weight, metabolic rate varied inversely with weight.