Summary
In fish, sex determination is a plastic process regulated by a relatively small number of genes that, in turn, leads to a cascade of organism level effects. In other animal taxa, intersexual variation is widespread and has implications in the realms of morphology, behavior, physiology, and bioenergetics. Although relatively well documented in the literature focusing on mammals, birds, and reptiles, the degree to which sex-specific variation is considered is unknown in fish and fisheries research. We examined the scientific literature to evaluate the important sex-related differences in fish and highlighted why some of these differences are of great biological consequence. Sex-specific differences in morphology included sexual size dimorphism, external traits such as coloration, and internal anatomy such as neuron structure. Behavioral differences between the sexes are often linked to reproduction, but there are some documented differences (i.e., variation in aggression and predator avoidance) that are independent of the reproductive period. The potential for sex-related physiological differences are relatively unexplored for fish, although there is strong evidence for disparity in hormone regulation, stress, and immune responses between the sexes. Sex-related variation is also poorly examined in the field of bioenergetics despite the fact that differences in energy requirements and expenditure should and do vary between the sexes. A quantitative literature review of several prominent fisheries journals revealed that sex is often overlooked in fish and fisheries research (between 15 and 44% of articles), which may impair the ability of researchers to detect biologically relevant differences, which in turn can greatly affect management decisions. Although there has been a growing recognition that intra-specific variation (at the population level) is important in fisheries management and research, there is also a need to consider that intersexual diversity exists and is important to understand, conserve, and manage fish and fisheries resources.
Methodology
Qualitative Literature Review
Between September and November 2006, a qualitative review of the examination or consideration of intersexual variation in fisheries research was performed to determine the current state of knowledge concerning intersexual variation in fishes. Four key areas (morphology, behavior, physiology, and bioenergetics) were identified, and the subsequent literature search was tailored to these areas. During this time period, ISI’s Web of Science (1945–present) was searched using the terms presented in Table 1. Results were then screened for relevance before inclusion in the literature review. Studies that did not specifically relate to intersexual variation and one of the key areas were excluded from further synthesis.
Quantitative Literature Review
In October 2006, a quantitative review of the utilization of intersexual variation in fisheries research was performed. Five years (i.e., January 2001 to December 2005) of five prominent fisheries journals were searched for references to intersexual variation or sex in each article contained therein. The journals were searched to determine if authors mentioned intersexual variation or considered sex as a variable in analysis during the study. These journals were North American Journal of Fisheries Management (NAJFM), Fisheries Management and Ecology (FME), Transactions of the American Fisheries Society (TAFS), Journal of Fish Biology (JFB), and Canadian Journal of Fisheries and Aquatic Sciences (CJFAS). These journals were selected because of our belief that they represent some of the key empirical outlets in the field of fish and fisheries, providing regional coverage in Europe and North America. Though there were only a minor proportion of articles published in these journals, it is important to note that most journals surveyed extend their definition of fish to include invertebrates (e.g., NAJFM, TAFS) and in some cases include research on plankton, marine mammals, and other aquatic taxa (e.g., CJFAS). In addition, some of these journals also publish perspectives (e.g., CJFAS) or research on human dimensions (e.g., NAJFM, FME) for which fish sex is not likely to be relevant. For the purposes of this analysis, we included all peer reviewed articles only and excluded editorials and book reviews. No temporal trends were observed while enumerating studies that included sex as a factor, permitting us to pool data for the 5 years to one set of measures per journal. The proportion of studies that included intersexual variation or sex was considered, and the between-journal comparisons were analyzed by chi-square contingency tables (Zar, 1999). Pairwise comparisons were performed to determine significant differences in a proportion of studies that included intersexual variation or sex in analysis between journals (Zar, 1999).