Growth energetics of juvenile herring, Clupea harengusL.: food conversion efficiency and temperature dependency of metabolic rate

The relationship between rates of food consumption (C) and somatic growth (G) and the effect of temperature (T) on rates of mass lost during food deprivation were examined in 9–10 cm total length (TL) [1.0–1.5 g dry mass (DM)] juvenile Atlantic herring (Clupea harengus L.) in the laboratory. One feeding-growth trial was conducted at 16°C using groups of herring feeding on known rations of brine shrimp (Artemia spp.) nauplii to quantify gross and net growth efficiency. Rates of mass lost by groups of herring (a proxy for metabolic rate, M) were measured in trials conducted at 9.7, 14.2 and 17.9°C. Gross growth efficiency (GGE = 100*G*C -1) at 16°C was 25% at the highest rations (5.8–6.6% DM). The maintenance ration (Cmain = C at zero G) was equal to 432 J*fish -1*d -1 or 2.0% DM*d -1. At 16°C, net growth efficiency (100*G*(C-Cmain) -1) was 42%. The nucleic acid content (RNA-DNA ratio, RD) in herring muscle tissue was strongly related to somatic growth (G, % DM*d -1 = -0.36*RD2 + 3.21*RD -3.92, r2 = 0.90, P< 0.05, n = 8 groups). The effect of T (9.7–17.9°C) on M was described by a second order polynomial equation M = -1.24*T + 38.2*T -218 (J*g DM -1*d -1) and M = -10*T + 310*T - 1815 (J*fish -1*d -1). This was the first study to investigate the influence of temperature on the metabolic rate of juvenile Atlantic herring under stress-free conditions in the laboratory and provides the first estimates of gross and net growth efficiency for this species feeding on live prey.