Buoyancy of Atlantic cod larvae in relation to developmental stage and maternal influences

In this experimental study on Atlantic cod, Gadus morhua, buoyancy was found to vary significantly with season, developmental stage, egg size and maternal condition. Before the start of the experiments, wild fish were caught in the Barents Sea and acclimatized to laboratory conditions. Pairs (n = 8), one female (recruit spawner) and one male, spawned naturally in large, indoor compartments of a circular tank and every third egg batch (out of up to 19 batches collected per female) was incubated in aquaria. Following sedation (50 mg l−1metomidate hydrochloride, 30 min), individual larval specific gravity was precisely reported (30 min) using a density-graduated column. Larval specific gravity (meanσt) increased steadily during the first early stages of development (0–25 day-degrees), remained nearly constant during the following stages (25–35 day-degrees), but then decreased gradually (35–55 day-degrees). In general, late-season larvae were significantly less buoyant, i.e. showed higher meanσt, than early-season larvae. Meanσtwas negatively correlated with female condition and egg size and dry weight. Possible implications of these findings for drift and survival are discussed.