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Fish reproductive investment is the result of essential life history trade‐offs in resource allocation (Stearns 1992). Energy that is surplus to the essential standard metabolic requirements (i.e., maintenance, locomotion, predation avoidance, and feeding activity) is allocated to somatic growth, energy storage, or reproduction after the fish reaches sexual maturation. The priority with which this surplus energy is allocated to each of the above biological functions differs among fish species (Calow 1985). In the case of North Sea plaice Pleuronectes platessa, Rijnsdorp (1990) proposed a hypothetical mechanism, postulating that energy in excess is first prioritized into the building of reserves, then into reproduction, and finally into somatic growth if surplus exceeds a certain threshold.
The interaction between reproduction and growth is one of the most important trade‐offs in fish (Stearns 1992) because most reproductive traits (especially female fecundity) and growth are a function of body size (Wootton 1998). Moreover, animals that have indeterminate growth (e.g., fish) must consider the survival costs and the available energy for reproduction and must make an allocation decision between current and future reproduction as an adaptation to the fluctuating environmental conditions. For instance, an increase in growth during the current spawning period would be associated with a decrease in offspring production during that period, but the resulting larger size of the fish could confer a benefit of increased fecundity in the subsequent reproductive season (Heino and Kaitala 1999; Tsikliras et al. 2007).
The trade‐off pattern between growth and reproduction might differ depending on the reproductive strategy of a fish species. For instance, most clupeiform fishes have indeterminate fecundity (the Atlantic herring Clupea harengus is an exception) and are characterized by a small size, high growth rates, a relatively short life span, and late maturity occurring at a large size relative to adult size such that energy is first allocated to growth and then to reproduction. On the contrary, in many gadiform fishes, fecundity is determinate (the European hake Merluccius merluccius is an exception) and these fish are characterized by a large size, low growth rates, a relatively long life span, and early maturation at a small size; thus, reproduction starts well before the growth rate declines (Rochet 2000