Variability in condition and growth of Atlantic cod larvae and juveniles reared in mesocosms: environmental and maternal effects

Abstract

Standard length, dry mass and RNA : DNA ratio measurements of 3876 Atlantic cod Gadus morhua larvae and juveniles from 26 families of recruit (fish during their first year of spawning) and repeat spawners (fish which were in their subsequent spawning season) reared in two mesocosms (2500 and 4400 m3) under semi‐natural conditions were analysed over a period of 10 weeks using microsatellites. Larvae from recruit spawners were significantly longer and heavier at hatch and throughout the 10 weeks. RNA : DNA ratios from recruit spawner offspring were only significantly higher at week 1. The smaller (2500 m3) mesocosm was characterized by low plankton density during the transition from endogenous to exogenous feeding followed by a higher density during the metamorphosis period (weeks 4 and 5), with the reverse pattern evident in the 4400 m3 mesocosm. Patterns of larval growth followed patterns of zooplankton density. Significant differences in RNA : DNA ratios between the mesocosms at all comparable sampling dates were found and within each mesocosm individual fish exhibited a wide range of growth and condition responses under the same environmental conditions. RNA : DNA ratios as a function of size differed in the amount of variability between mesocosms, indicating that the higher food density led to a higher proportion of well‐conditioned larvae in the first 3 weeks. Food availability probably has a major role in determining offspring growth and condition, with limited effects due to maternal effects in cases where the broodstock females are approximately of similar size and condition.

On the edge of death: Rates of decline and lower thresholds of biochemical condition in food-deprived fish larvae and juveniles

“…Biochemical condition (RD) is one of the most widely used growth indicators for marine fish early life stages (e.g., Buckley, 1984;Buckley et al, 2008;Chícharo and Chícharo, 2008;Clemmesen et al, 2003). Recent research has standardized this ratio (sRD) allowing comparison of measurements made in different laboratories .…”

“…Such phenotypic variability may arise from physiology (Peck et al, 2004a) or genetic differences among individuals (Case et al, 2006;Clemmesen et al, 2003;Saborido-Rey et al, 2003), and can be exacerbated by behavioral interactions among individuals (Moran, 2007). Despite the best efforts to reduce this variability, laboratory-reared groups often contain individuals having different nutritional or growth status.…”

Trophic flexibility in larvae of two fish species (lesser sandeel, <i>Ammodytes marinus</i> and dab, <i>Limanda limanda</i>)

“…RNA and DNA concentrations of whole individual larvae were analyzed using a modification of the method by Clemmesen et al (2003). Samples of lesser sandeel and dab were thawed and standard length was measured using a stereomicroscope.…”

Estimation of Male Reproductive Success of Marine Fisheries

“…Pooled family rearing is costly due to necessary DNA analysis, and in itself should also be replicated, which is rarely done. Studies to monitor the growth and survival of larvae originating from specific families of pleuronectoids and gadoids are rare (e.g., Chambers and Leggett, 1992;Clemmesen et al, 2003). It is anticipated that greater gains in this area will occur as the development of aquaculture breeding programs for species of these taxa advance over the next ten years.…”