Effects of food density on growth and on patterns of prey depletion by larval silverside fish, Menidia beryllina (Cope); a laboratory investigation with image analysis

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The growth and daily prey depletion rates of inland silverside (Menidia beryllina (Cope)) larvae fed different rations (0, 25, 50, 100, or 150 percent of the fishes' initial wet weight) of Artemia nauplii during the period 7 days to 14 days post-hatch were investigated. Instantaneous growth rates ranged from -0.174·day-1 for unfed fish, to 0.181·day-1 for fish fed the 150% ration. Relative consumption rates increased from 0.179 (mg food·(mg fish)-1·day-1) at the lowest ration (25%) to 0.440 (mg food·(mg fish)-1·day-1) at the highest ration (150%) and were linearly related to relative growth rates (mg·(mg fish)-1·day-1) across the range of consumption rates studied. Gross growth efficiencies ranged from -0.020 to 0.376, from lowest (25%) to highest (150%) ration. On one day of the 7-day study, the within-day patterns of food depletion by the fish also were examined with image analysis. Fish ingested food at a constant rate, as long as it was available up to 11 h of feeding. On average, depletion rates in the first 4 h of feeding were not significantly different among fish fed the four rations; however, the depletion rates of the fish fed the 150% ration were significantly higher during the second 4 h of feeding than during the first 4 h. The results provide information for the calculation of a preliminary energy budget for M. beryllina, and also provide aquatic toxicologists with information for the conduct of standard effluent toxicity tests. The daily ration prescribed in the current standard method is approximately three times the amount that can actually be ingested by the larvae. Through the use of our data and image analyzer measurements of food consumed by M. beryllina in the 7-day test, investigators might be better able to identify causes of reduction in growth. © 1993.

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Journal of Experimental Marine Biology and Ecology