Reproductive Strategies in Flatfish: A First Synthesis

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Abstract
The factors determining the age and size at maturity of temperate species of flatfish were examined. In some species maturity is governed by size, not age. The most likely determinant of this size is size-dependent predation. Many species fast during the winter months and rely on reserves stored in the body tissues to provide energy for gonad maturation. The stress placed on a fish by the breakdown of body tissues may be very substantial and could significantly affect the predation function. Under these conditions, selection may favor the deferment of maturity until a size is achieved at which predation is relatively low. Such a mechanism may account for the extreme geographic variation of life history of American plaice, Hippoglossoides platessoides and witch flounder, Glyptocephalus cynoglossus. The generality of winter cessation of feeding suggests that the above hypothesis may also be applicable to a wider range of species. By contrast, in several species, age has been more important than size in determining the onset of maturity. Age is likely to be more important than size in early maturing species; in these a decrease in the age at maturity may be, temporarily at least, prevented by genetic/physiological constraints imposed by the time required for oocyte development. This hypothesis is tested and supported by historical data on several European species. The intra- and inter-specific patterns of allocation to fecundity are examined. Interspecific differences in allocation to reproduction are greatly reduced but not eliminated when egg volume is taken into consideration. Factors influencing the observed allocation patterns are examined.