Individual food intake measurement of freshwater crayfish (Pacifastacus leniusculus Dana) juveniles

Abstract

The inert marker method for individual food intake measurement of signal crayfish (Pacifastacus leniusculus Dana) juveniles (carapace length (CL) ranged from 16.5 to 25.6 mm and wet weight (WW) from 0.88 to 4.47 g) was evaluated in a series of experiments. The measurement technique was tested with two types of diet: a gelatin-based semi-moist diet and an agar-based dry diet. Diets were labelled with X-ray dense ballotini glass beads. After feeding, juveniles were X-rayed, and the amount of ingested glass beads in the digestive track was counted from the X-ray images. The method proved reliable only with the gelatin diet. In the ingested gelatin food, 92.80±8.55% of the glass beads originally in the food were found in comparison with 40.99±24.72% for the agar diet. Subsequently, the growth efficiency of the gelatin diet was compared with typically used raw fish diet (roach, Rutilus rutilus L.), and possible harmful effects of X-raying on the growth and survival of the juveniles were tested on 2-year-old crayfish (CL 22.90±1.66 mm and WW 3.15±0.71 g). Roach-fed juveniles grew significantly faster than the gelatin-fed counterparts. However, the growth performance and survival of the juveniles on gelatin diet was considered good enough to allow long-term growth experiments with individual feed intake monitoring, e.g. for studies on social behaviour of the crayfish. The results of this study confirmed that the X-radiography technique together with a semi-moist gelatin-based diet makes it possible to measure individual food consumption of freshwater crayfish juveniles reared communally.