The rabbitfish Siganus guttatus is an important tropical aquaculture species, but fry production is hampered by availability of ideal live feeds. This study investigated the predatory functional response of S. guttatus early juveniles on live brine shrimp nauplii (Artemia franciscana), rotifers (Brachionus plicatilis), and wild copepods. The predation experiment comprised one individual fish of different (small, medium or large) sizes, and either of the three live zooplankton prey at four to six increasing densities in a sealed 1-L plastic bottle with filtered seawater. An experiment was replicated five times, and fish and prey were kept suspended in a plankton roller. Videography and gill raker analysis were done to further understand feeding mechanism. Highest fish consumption rates were on Artemia nauplii, but only medium and large size fish showed a Holling’s type II model with peak consumption at 15 nauplii mL-1 concentration half those regularly provided to the fish in the current rearing practice. The functional response of small fish on Artemia was dome-like. Only the large size fish successfully ingested copepods and the functional response was directly proportional. Rotifers were only ingested by small fish that showed an inversely proportional response. The deviations from Holling’s models were attributed to fish size, Artemia nauplii size, highly evasive behaviour of copepods and the small size of rotifers. This study identified ideal Artemia nauplii concentration to S. guttatus early juveniles, but evasive prey behaviour of wild copepods and small size of rotifers render these prey types less ideal for early juvenile S. guttatus.
