Frog farming: Investigation of biological and mechanical agents to increase the consumption of pelleted food by adult Rana temporaria
The requirement of moving prey for eliciting feeding behaviour is typical of anurans, and is one of the major difficulties of rearing frogs. This difficulty can potentially be solved by using mechanical devices to move the food, or by mixing inert food with live prey. This study investigated consumption of pelleted food by adult common frogs, Rana temporaria, when moved by a mechanical stirrer or by fly larvae. The mechanical device did not produce higher consumption than inert pellets alone. Fly larvae significantly increased consumption of food pellets, whether these were mixed together, or the larvae were isolated below the pellets by a flexible membrane. Consumption was similar whether the membrane was sealed or perforated, so that movement of the pellets, rather than the scent of the fly larvae, was the stimulus that increased pellet consumption. Frogs did not apparently learn to feed on pellets, with no increase in consumption through the experiment of either control inert pellets or of pellets moved by fly larvae. Consumption (of dry mass) of pellets was similar to that of live crickets by frogs in the same conditions. Frogs consumed significantly more xenopus pellets (produced for aquatic Xenopus toads) than trout pellets from an equal mixture, both by number and mass. The two types of pellet had similar nutritional composition but differed in texture, smell, size and mass, and colour; xenopus pellets being larger (82 mg and 50 mg, respectively) and darker. Any combination of these differences could have caused the difference in consumption, with colour being most likely, darker pellets presenting greater contrast against the white background of the feeding dishes. The difference in consumption shows that optimisation of pellet characteristics, such as the incorporation of a dark dye, could be important in large-scale frog culture.