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Abstract The African clawed frog, Xenopus laevis, has been used as a laboratory animal for decades in many research areas. However, there is a lack of knowledge about the nutritional physiology of this amphibian species and the feeding regimen is not standardized. The aim of the present study was to get more insights into the nutrient metabolism and feeding behavior of the frogs. In Trial 1, adult female X. laevis were fed either a Xenopus diet or a fish feed. After 4 weeks, they were euthanized, weighed, measured for morphometrics and dissected for organ weights and whole-body nutrient analysis. There were no significant differences between the diet groups regarding the allometric data and nutrient contents. The ovary was the major determinant of body weight. Body fat content increased with body weight as indicator of energy reserves. In Trial 2, 40 adult female frogs were monitored with a specifically developed digital tracking system to generate heat-maps of their activity before and up to 25 min after a meal. Three diets (floating, sinking, floating & sinking) were used. The main feed intake activity was fanning the feed into the mouth, peaking until 20 min after the meal. The different swimming characteristics of the diets thereby influenced the activity of the animals. Our dataset helps to adjust the feeding needs to the physical composition and also to meet the natural behavioral patterns of feed intake as a prerequisite of animal wellbeing and animal welfare in a laboratory setting.

Morphometric data that provide information on body conditions can be used to monitor the health and well-being of animals. In laboratory animals, they can help to evaluate the stress due to experiments or treatments, following the 3R principles. The aim of the present study was to obtain morphometric data of male and female African clawed frogs, Xenopus laevis, as the bases for body condition evaluations. Adult frogs (n = 198) were weighed and standardized photographs were taken. The photographs were used to determine several measurements (length, cranial width, caudal width, thigh width). In addition, a triangle was drawn to outline each frog’s simplified body form, and the triangle surface was calculated. In conclusion, the triangle surface drawn on the dorsal plane of each frog correlated with the body weight of the females. There were significant differences between the body weights and sizes of male and female frogs, with males being smaller (p < 0.001). Based on the morphometric data, females could be assigned to five groups in which an assessment of the animal’s well-being is feasible.

African clawed frogs are common animal models used in various research areas. However, husbandry and especially feeding regimens are not nearly as standardized as is established for other laboratory animals. We recorded the diets and feeding protocols commonly used in laboratory practice in a questionnaire (18 responses). The survey revealed a wide variety of housing conditions. Feeding protocols and, in particular, diet composition varied considerably between facilities. While diets tailored to Xenopus were used in the majority, differences in feeding frequency and dietary components were noted. From five responses, the weekly feed intake per frog could be calculated, showing considerable differences in dry matter intake (1.37–5.4 g). The labelled nutrient content of the diets fed in the facilities (n = 10) met the recommendations in most cases, with protein as the major energy source. However, the mineral content varied markedly between diets. Both floating and sinking diets were used, while quickly sinking diets were associated with feed leftovers. Feed processing may likely influence feed intake behavior. Further research is needed to ensure standardization for aquatic species with respect to husbandry systems, feeding regimens, and especially the nutrient composition of feeds. Furthermore, this work will contribute positively to animal welfare and the comparability of research results.