Bioenergetics of growth of a cyprinid, <i>Phoxinus phoxinus</i>: the effect of ration, temperature and body size on food consumption, faecal production and nitrogenous excretion

Abstract

Food consumption, faecal production and nitrogen excretion by minnows, Phoxinus phoxinus , weighing 1–5.5 g were studied at five rations ranging from starvation to ad libitum and four temperatures ranging from 5 to 15°C. The maximum rate of food consumption (C max ) was related to body weight ( W ) and temperature ( T ) by the relationship: C max = aW b1 T b2 . There were significant daily variations in C max , which tended to decline over time. Absorption efficiency increased with increasing ration size and decreasing temperature. Body weight had no significant effect on the faecal production. The equation F = a C b1 e b2 T described the relationship between faecal production ( F ), food consumption ( C ) and temperature. Ammonia‐N predominated over urea‐N in the excreta of most experimental fish. The proportion of urea‐N in the total nitrogen excreted was generally higher at lower rations than at higher rations. Rates of nitrogen excretion increased with increased ration size and were, to a lesser extent, influenced by temperature. Body weight had no significant effect on the nitrogen excretion by feeding minnows. The equation N = a+b l T+b 2 C described the effects of food consumption and temperature on nitrogen excretion ( N ) other than urea‐N excretion. The relationship between urea‐N excretion ( N u ), food consumption and temperature was described by the equation N u = ae b1T ((C+1) b 2. On the average, 11 % of food energy was lost in faecal production and nitrogen excretion by minnows feeding on whiteworms, Enchytraeus spp.