SynopsisFish species richness in 82 lakes in Ontario, Canada was significantly correlated with surface area. In this region, latitude explained only a small amount of the variation in fish species richness. Thus, our study provides a clear demonstration of the relation between fish species richness and lake area without the confounding effects of latitude and physiography inherent in analyses from broader geographic regions. By comparison with the species-area relationship obtained, we show that acidification clearly depressed the number of fish species in 66 acid-stressed lakes in Ontario. Fish species richness was also significantly correlated with both drainage and surface areas of 21 Ontario rivers. Slopes of species-area regressions of lakes and rivers did not differ significantly, suggesting that species are added to these habitats at similar rates. However, our regression analyses show that rivers support more species of fish per unit surface area of water. Although these results are consistent with some predictions of Island biogeography theory, we suggest that fish species richness is more likely to be a simple function of habitat diversity, rather than an equilibria1 balance between immigration and extinction.

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Ten experimental broods of red-winged blackbird (Agelaius phoeniceus) nestlings, experimentally manipulated to contain two males and two females of similar age, were observed with the aid of video cameras to determine (a) which nestling characteristics were most important in influencing its chances of being fed and (b) if males and females differed with respect to these characteristics. Nestlings that could reach highest while begging were most successful at obtaining food from parents during individual feeding bouts. However, while there was a tendency for nestlings that begged earlier to be offered food first, a nestling's position in the nest during these bouts did not influence its feeding success. Males begged more than often females and were offered more food by parents. Males were also more likely to be fed when they begged. This was most likely because males, being larger than females, were able to reach higher while begging. Neither sex was more likely to beg sooner or occupy certain positions in the nest. However, while males that had been transferred from other nests received less food than natal males, there were no differences in food acquisition between transferred and natal females. Differences in the relative success of males and females under different conditions may help explain differences in fledgling sex ratios observed in many dimorphic species.

Japanese medaka (Oryzias latipes), a small freshwater fish used extensively to investigate sexual differentiation and development, were exposed to octylphenol (OP), a known estrogen agonist, to assess its impact on reproductive success. Male and female medaka were exposed to nominal concentrations of 10, 25, 50, and 100 μg/L OP from 1 d posthatch to 6 months posthatch. In reproduction trials involving exposed males and unexposed females, the males exposed to nominal concentrations of 25 and 50 μg/L showed a reduction in some courtship activity and overall reproductive success. Eggs produced by matings of exposed males and females demonstrated various developmental problems, including circulatory system difficulties, incomplete eye development (i.e., anisophthalmia), and failure to inflate swim bladders upon hatch. One male fish with an intersex gonad was able to fertilize the eggs of an unexposed female. This study is one of the first to show the possible behavioral and transgenerational effects of an estrogenic compound on the reproductive success and second generation embryo‐larval development of fish.