Respiration and growth of larval herring Clupea harengus: Relation between specific dynamic action and growth efficiency

Rates of growth and oxygen consumption were measured in larval herring Clupea harengus fed various rations (specific ingestion rate between 0 and 45 % body wt d⁻¹). Initially, growth increased linearily with ingestion. However, it showed a saturating response at high ingestion rates, probably caused by a decline in assimilation efficiency.

Growth efficiency was expressed as slope of the linear portion of the growth-ingestion (or growth-assimilation) relationship. The efficiency by which ingested (or assimilated) material in excess of maintenance requirements was converted to larval body mass was high, 0.62 (or 0.89), compared to reported estimates in juvenile fish.

The oxygen consumption rate (R, ng O₂ h⁻¹) of anaesthetized larvae could be separated into two components, one proportional to the body mass (W, μg dw) raised to some exponent b and one component proportional to the growth rate (μ × W, μg dw d⁻¹): R = 131 W0.68 + 127 μ × W. At starvation, the respiration-mass relationship followed the commonly applied allometric equation and had a weight exponent close to the classical ⅔.

Growing larvae, however, increased their rate of oxygen uptake above the starvation level by ca 127 ng O₂ per μg larval dry weight increment (= apparent metabolic cost of growth = specific dynamic action (SDA) expressed relative to growth). This empirical estimate was close to a theoretical minimum estimate of the cost of biosynthesis and transport but was in the lower range of the empirical values reported for juvenile fish.

The observed SDA predicted a growth efficiency very close to that actually observed. The magnitude and composition of SDA in larval and juvenile fish is discussed and it is concluded that the cost of growth is minimum and the efficiency of growth maximum in larval compared to juvenile fish. In an ecological context, this difference may be related to the very steep decline in natural mortality with increasing fish body mass and to the extraordinarily high mortality rates experienced by marine pelagic fish larvae in nature.