Laboratory experiments on mechanisms of competition and resource partitioning between Menidia menidia (L.) and Menidia beryllina (Cope) (Osteichthyes:Atherinidae)

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Postlarvae of two atherinid species, Menidia menidia (L.) and Menidia beryllina (Cope), were tested in two 14-day experiments at four densities of fish to determine effects of interspecific versus intraspecific competition for food. In one experiment, when M. menidia was slightly larger than M. beryllina (simulating a slightly earlier hatching time in nature) M. menidia exhibited a clear competitive advantage over M. beryllina, as demonstrated by covariance analysis of fish biomass change on fish density. In the second experiment, when M. beryllina was larger than M. menidia, neither species showed competitive advantage. The results suggest that M. menidia has an inherently superior ability to compete for food. Results of the experiment in which M. menidia was the larger species indicate the selective pressures which could have caused the two species to evolve spawning times ≈1 month apart. In another set of experiments, post-larval and juvenile M. menidia and M. beryllina were fed wet weight rations of Artemia nauplii ranging from 10-640% of initial body weight per day during a series of three 10-day feeding trials. As Menidia menidia grew, they required a smaller percentage of body weight per day in food for maximum growth (640, 320, and 160% for the three feeding trials). The same trend was observed with M. beryllina, although the percentages (160, 160, and 80%) were much less than those for M. menidia. Menidia menidia also required more food per day (20-135% of body weight) as a minimum ration for survival and growth than did M. beryllina (5-60%). The explanation for these differences may be that M. menidia in nature hatch earlier in the year, when Zooplankton is more abundant, than do M. beryllina. The two species have apparently evolved different feeding requirements as adaptations to the different food availabilities that they encounter. © 1985.

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Journal of Experimental Marine Biology and Ecology