Functional responses during the early larval stages of the charal fish Chirostoma riojai (Pisces: Atherinidae) fed rotifers and cladocerans

Survival during early fish larval stages depends largely upon the availability of appropriate prey. Studied were the functional responses from hatching to 6 weeks of age of whitefish (Charal) (Chirostoma riojai) larvae that were offered selected rotifers (Brachionus rotundiformis and B. rubens) and cladocerans (Moina macrocopa and Ceriodaphnia dubia). The experiments were conducted in a 50 ml medium at a salinity of 2 g L^?1. Each treatment used four replicates. Rotifers were introduced at densities of 0.5, 1, 2, 4, 8 and 16 individuals ml^?1 and cladocerans at 0.1, 0.2, 0.4, 0.8, 1.6, 3.2, 4.8 and 6.4 individuals ml^?1. Two larvae, previously starved for 2 h, were introduced into each test jar and allowed to feed for 45 min. The difference between the initial and final zooplankton density represented prey consumption. C. riojai larvae showed Type II functional response curves, i.e. they consumed more zooplankton with increasing prey availability; above a certain prey density (8–16 individuals ml^?1 in rotifers and 3.2–6.4 individuals ml^?1 in cladocerans) the consumption rate tended to stabilize in most trials. Results are discussed in relation to aquaculture.