Quantitative Feeding and Weight Changes in Poecilia Reticulata

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Abstract
A total of 298 juvenile guppies, P. reticulatus, approximately 1 cm in length was divided into 4 groups. Of these, 282 lived until termination of the experiments. One group was sacrificed at once, whereas the other 3 were maintained in a growth chamber at 26.7 C [plus or minus] 0.5[degree], with 4 hr. of light and 20 of darkness per day. Experimental fish were fed daily 10 Daphnia pulex, size 1.8 mm, consuming on the average 8.8 per day per fish. Control groups were starved, or fed maximally on a mixed diet. At the termination of each of 8 experiments, all fish were sacrificed, and their wet, dry and ash weights were ascertained. Organic matter weights were taken as the difference between dry and ash weights. The well-fed controls nearly doubled in weight. Starved controls lost over 1/4 of their weight. Experimental fish gained on the average slightly in wet weight, but they lost 9.8% of their dry weight, and 13.3% of their organic matter weight. Wet weights were considered somewhat unreliable. The calculated maintenance requirement of the guppies was 13.8 daphnids per day on the basis of the dry weight of the fish, and 16.9 daphnids per day on the basis of their organic matter weight. In order to gain maximally, the rate of consumption would have to be respectively 64.7 and 69.7 daphnids per day. Based on these results and those of D. pulex grown on Chlamydo-monas reinhardi, it is estimated that the dry weight ratios of the food chain: C. reinhardi[forward arrow] D. pulex[forward arrow]P. reticulatus would be 80.2 : 3.5 : 1.0 for maximum growth. Efficiency of transfer of organic matter from D. pulex to P. reticulatus was estimated to be 23.3% for dry weights and 28.2% for organic matter weights. These figures were within the rather wide range previously given by other authors for transfer of matter from herbivorous to carnivorous fish. This range, which was summarized, lies between less than 7 and 56%.