Differences in growth pattern between spring and autumn spawned herring (Clupea harengus L.) larvae

Abstract Otolith and somatic growth of herring (Clupea harengus L.) larvae were studied in laboratory experiments (500-litre tanks) in autumn 1995 and spring 1996. The larvae were kept at 8 °C and offered natural zooplankton at low (20–40 prey I-1) or high prey densities (1200–2000 prey I-1), and simulated seasonal photoperiods were used. Mean growth rates in length were higher in spring than in autumn both when offered low (0.12 mm d-1 v. 0.08 mm d-1) and high (0.35 v. 0.24 mm d-1) prey densities. Average weight-specific growth rates (G) were 1.7 % d-1 at low and 6.7 % d-1 in the high density groups. Autumn spawned larvae showed a dome-shaped growth pattern with a maximum in growth about 3–4 weeks post hatching, whereas spring spawned larvae grew at approximately constant rates during the same period. Daily mortality rates were less than 2.5 % in all groups. Otolith radii were not significantly different at similar lengths in autumn- and spring-spawned larvae.