The effect of temperature on the rate of passage of food in the smallmouth yellowfish, <i>Barbus aeneus</i> Burchell (Teleostei, Cyprinidae)

Abstract

The effect of temperature on the rate of gut evacuation in Barbus aeneus was investigated in two ways. In the first, juvenile fish, kept under conditions of constant temperature, were fed marked food items and the time elapsing until these appeared in the faeces was noted. In the second, fish of a range of sizes were caught in the P.K. le Roux dam and immediately placed in cages in the dam to prevent their access to food. Groups of fish were sacrificed at intervals and the contents of standardized gut sections weighed. The field experiment was carried out in summer and in winter. The laboratory experiment yielded the relationship: P = 6270 × T^-2,11 where P is the passage time in hours and T is the temperature in °C. This gives passage times of the order of 8 h at 25°C and 39 h at 11,5°C. The field experiment indicated that there was an exponential relationship between degree of fullness and rate of evacuation, and that complete evacuation required about 24 h in summer, but more than 5 days in winter.