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Abstract: A significant part of the variation in the early life history traits of fish can be ascribed to the parental origin of the individual larvae. The primary source of this parental contribution has been attributed to maternal effects and evidence for paternal effects is equivocal. Maternal effects are a non-genetic contribution of a female to its offspring but most reported maternal effects are products of both genetic and non-genetic contributions, i.e. female effects. In this study, parental effects on traits of larvae of Atlantic herring (Clupea harengus L.) at hatch were investigated at one temperature using a 5×3 factorial mating design (North Carolina Design II). This allowed estimation of the true maternal effect and the additive genetic variation (heritability). Furthermore, relationships between individual traits were examined and for the first time nucleic acid content and otolith size at hatch were examined together. A significant correlation between the two was found and it is argued to support the notion that otolith growth is more related to metabolic rate than to somatic growth. Maternal effects were detected in larval weight and yolk-sac volume, while paternal and, hence, genetic effects appeared in larval length, yolk-sac volume, RNA:DNA ratio, and lapillar area. The findings suggest that an increased emphasis should be placed upon the importance of male influence on success of early larval fishes. [Copyright &y& Elsevier]

Abstract: Besides variable egg survival, previous studies suggested that the larval stage may be the most critical phase in determining Baltic cod recruitment variability, and that larvae need to conduct an ontogenetic vertical migration from hatching depths (>50m) to upper layers with increased food availability in order to initiate first feeding, improve their nutritional condition and growth, and avoid starvation. Recently, detailed information on the stage-resolved vertical distribution of main Baltic copepod species, including the preferred larval Baltic cod prey species Pseudocalanus acuspes, has become available. Therefore, the vertical distribution of Baltic cod larvae in August 2007 and their depth-dependent nutritional condition and growth were investigated. RNA–DNA based methods were used to estimate growth, including a novel approach to estimate growth performance by relating observed specific growth rates (SGR) of field caught larvae to temperature-dependent reference growth rates (Gref) for fast-growing laboratory reared fish from the literature. This standardization to Gref was found to have a great potential to improve investigations on the growth and ecology of larval fish. The need for early larvae to migrate to shallower layers was corroborated, while larger size classes were found at increasingly greater depths. This may reflect a continuation of the ontogenetic vertical migration in order to follow increasingly larger prey items at greater depths and to save energy in cooler waters below the thermocline. Larval growth generally declined with increasing depth, but the decline in growth became less pronounced in larger size classes. This indicates that larger larvae were better in coping with the ambient environment and the available prey field at greater depths. Generally, Baltic cod larvae grew poorly compared to larvae from other studies, which is discussed in relation to differences in predation and a possible food–temperature trade-off for larvae in the highly stratified Baltic Sea. Comparison with earlier results showed a higher frequency of starving larvae and lower frequencies of larger larvae after the first-feeding stage in 1994 and 1995. As this was a period of low Baltic cod recruitment despite favourable conditions for egg survival, it is concluded that larval starvation mortality has a high potential to contribute to recruitment variability in Baltic cod. [Copyright &y& Elsevier]