Some aspects of the metabolism of brown trout and perch

Abstract

Using recirculating water fish tunnel respirometer, the metabolism of brown trout, Salmo trutta (L) and perch, Perea fluviatilis (L), was investigated. The fish were subjected to increasing velocity swimming tests at 5°C, 10°C and 15°C. After swimming failure, following the final speed increase, the recovery of the fish was monitored for a period of three hours. Whilst undergoing the routine and active metabolic conditions of the experiments, analyses were carried out on the uptake of oxygen and excretion of carbon dioxide and ammonium nitrogen. A new method for the analysis of carbon dioxide in fresh water was described, based on the so called carbon dioxide electrode. The measurements made enabled the respiratory quotient to be estimated. It was found that brown trout, undergoing routine activity, catabolised the same percentage (287.) of protein at both 5°C and 15°C, in relation to the total metabolism at each temperature. The lipid and carbohydrate contributions to the total metabolic rate, however, demonstrated a marked temperature effect. At 5°C lipid provided 49% of the total energy utilised 'and carbohydrate 22%. At 15°C the situation was reversed, lipid providing 27% and carbohydrate providing 46% of the total energy utilised. At 5°C and 10°C brown trout maximum sustained swimming speeds were accompanied by a catabolic metabolism comprised of 70% lipid oxidation. At 15°C the swimming metabolism of brown trout was suggested as being characterised by a hetogenic condition coupled with a gluconeogenesis. Perch active metabolism at all three temperatures indicated a strongly anaerobic energy supplying mechanism was operating. The perch routine metabolism, measured at only two temperatures, 10°C and 15°C also showed a temperature effect. In contrast, however, to brown trout; as the temperature decreased lipid oxidation also decreased. The recovery metabolism for both brown trout and perch enabled an hypothesis to be propounded relating to acid base balance. It was suggested that brown trout, which appeared to resist overt anaerobic metabolism, possess a system of NH4+ excretion which can utilise metabolically produced H+ ions to maintain blood pH stability. This hypothesis was discussed in relation to the findings of the study and previously reported observations.