Archard, G. A. 2012. Effect of enrichment on the behaviour and growth of juvenile Xenopus laevis. Applied Animal Behaviour Science 39(3-4), 264-270.

Xenopus laevis is the most widely used model amphibian species in laboratories, yet there is almost no experimental evidence to guide best practice for captive housing. Enrichment is an important component of maintenance and welfare. A split-sibship experimental design was used to rear juvenile X. laevis under one of three treatments for 30 weeks: a control with no enrichment, enrichment from plastic drainpipe, or enrichment from a plastic plant. Location and clustering behaviour were quantified, along with the amount of food eaten and the time to start eating. Many Xenopus users work with eggs or embryos, and are concerned with the growth and size of animals because female size determines reproductive output. Snout-vent length (SVL) and mass were therefore measured every 3 weeks. After 30 weeks, final measurements included fat body mass in both males and females, and ovary mass and stage of development in females. Enrichment did not effect the time to start eating, or the amount of food eaten, and there were no differences in growth (SVL or mass) between treatments. There were also no differences in final mean per tank body mass, SVL, head width or fat body mass, or the coefficients of variation of these per tank measures. Ovary mass and developmental stage were both correlated with final body mass, but there was no effect of enrichment on these measures of female reproductive potential. However, there were clear differences in behaviour between treatments. Animals used enrichment in a variety of ways. Animals in tanks with drainpipes lay inside or alongside the pipe. Animals in tanks with plants lay under, against the base of, or among the fronds of the plant. Plants were used more than drainpipes, but enrichment in either form resulted in animals spending less time against the edge of tanks, and less time clustered together. Animals from enriched tanks also had smaller startle responses, suggesting they may have been less stressed. They were harder to catch in tanks than controls, but this was the result of the enrichment itself: once the enrichment was removed there was no difference in capture times. Overall, there is no evidence that enrichment limited the growth or reproductive potential of X. laevis, and clear evidence that they used it when it was available. Enrichment should therefore be provided to captive X. laevis as standard unless there is a well-defined reason not to do so.