Use of biochemical indices for analysis of growth in juvenile two-spotted gobies (&lt;i&gt;Gobiusculus flavescens&lt;/i&gt;) of the Baltic Sea

Andrea Frommel,Catriona Clemmesen

doi:10.3989/scimar.2009.73s1159

Abstract

Multiple biochemical measurements were evaluated as an indirect measure of juvenile fish growth rate. Juvenile two-spotted gobies, Gobiusculus flavescens (Fabricius), caught in the Kiel Bight, were incubated in a temperature gradient table at 7 different temperatures ranging from 9 to 22.7°C for up to 28 days and sampled weekly. RNA/DNA ratios (RNA/DNA), protein and lipid amounts were measured in whole fish homogenates and compared with calculated weight-based growth rates of the individuals. RNA/DNA values were not significantly correlated with weight-specific growth rates. Lipid- and protein-based growth rates, on the other hand, were highly correlated with weight-specific growth (R2 of 0.4-0.5) and lipid-based growth rate explained 45.8% variability of weight-based growth in a linear growth model. Weight-based growth rates showed a dome-shaped relationship to temperature with a maximum around 16°C, a trend mirrored in lipid-based growth rates. The results indicate a stage-dependent shift in energy storage and metabolism with a decoupling of RNA/DNA as an index of weight-based growth rate as the juvenile gobies mature and lipids become the main determinant of weight-based growth in these fish.

Highlights

The importance of larval growth and survival for fish stock recruitment has been recognised for a long time (Hjort, 1914), as described by the “growthmortality hypothesis” that predicts the survival of fish larvae to be directly related to growth, as the predation pressure decreases with increased size of the larvae (Shepherd and Cushing, 1980)
The percent mortality in the food-deprived control groups was at least 5 times higher than that in the fed groups at all temperatures examined
A multiple linear regression model including instantaneous dry weight growth rates (GiDW), lipid changes (GiL) and protein changes (GiP), along with a temperature term, confirmed that lipids are the main factor contributing to weight-based growth, while proteins play only a marginal role and temperature did not significantly affect the relation between growth rate in lipids (GiL) and growth rate in dry weight (GiDW). These results indicate a decoupling of DW growth rate and RNA/DNA due to the constant level of protein synthesis regardless of weight, developmental stage and condition, while lipid deposition increased at this developmental stage

Summary

Introduction

The importance of larval growth and survival for fish stock recruitment has been recognised for a long time (Hjort, 1914), as described by the “growthmortality hypothesis” that predicts the survival of fish larvae to be directly related to growth, as the predation pressure decreases with increased size of the larvae (Shepherd and Cushing, 1980). To estimate recent growth in the field, a method has been established in which RNA/DNA values are measured in field-caught young fish and related back to a laboratory calibrated relationship between RNA/DNA and a weight- or size-based growth rate specific to each species and developmental stage (Buckley et al, 2008; Caldarone, 2005). These predictions are important in estimating the recruitment of young fish to the reproducing stock of the population in order to forecast future stock sizes and, for example, to set fishing quotas for commercially exploited species

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