A functional model for maximum growth of immature stone loach, Barbatula barbatula, from three populations in north-west England

1. The chief objective was to develop a functional model for growth of stone loach, Barbatula barbatula, using immature fish from three populations. The growth model had been developed previously for brown trout, Salmo trutta, but new estimates of the five parameters for the stone loach had to be obtained from laboratory experiments. 2. Fish from four size groups (initial arithmetic mean live weights 0.053 g, 0.231 g, 0.840 g, 1.612 g, with five fish per group) from Great Oaks Wood Beck were acclimatized to constant temperatures of either 3, 5, 10, 15, 20 or 25 °C. Each fish was kept in a separate tank and fed to satiation on freshwater shrimps. Weights and lengths of each fish were recorded at the start and finish of a growth period of 35 days. For each of the other populations (Black and Ford Wood Becks), there were only three temperatures (5, 10, 20 °C) with ten fish per temperature. 3. The growth model was an excellent fit (P < 0.001, R2 > 0.99) for the 120 fish from Great Oaks Wood Beck. Growth rates were negative at 3 °C, close to zero at 5 and 25 °C, and positive at 10, 15 and 20 °C, with an optimum value of 19 °C. When growth rates were positive, they decreased markedly with increasing fish weight for small fish but decreased more slowly for larger fish. At the start of the experiments, weight–length relationships were similar for fish from all three populations and were well described by a power function. There was excellent agreement between growth rates estimated from the fitted growth model for fish from Great Oaks Wood Beck and values obtained for fish from Black and Ford Wood Becks. Data from all three populations were therefore pooled (n = 180) to obtain new estimates of the five parameters in the model. 4. Comparisons between parameter estimates for trout and stone loach showed that the latter grew better in warmer waters (e.g. optimum value for growth was 19.0 °C for stone loach and 13.1 °C for trout, with ranges for growth of 5.0–25.0 °C and 3.6–19.5 °C, respectively).