Feeding, physiology and growth responses in first-feeding gilthead seabream (Sparus aurata L.) larvae in relation to prey density

The effects of prey density (0.1, 1 and 10 rotifer ml(-1)) on feeding, oxyg en uptake, growth, survival and energetic efficiencies in Sparus aurata lar vae were investigated. Dry weights and total lengths at day 15 after hatchi ng were similar in larvae fed with 10 and 1 rotifer ml(-1) but were signifi cantly higher than in larvae fed with 0.1 rotifer ml(-1). These differences were a consequence of a delay in starting feeding and growth in larvae fed with the lowest rotifer concentrations tested. Growth rates were similar i n larvae fed on 0.1 and 1 rotifer ml(-1), while larvae fed with 10 rotifers ml(-1) showed the smallest growth rate. Survival decreased markedly (from 91 to 7%) when prey density decreased. Ingestion rates of the actively feed ing larvae increased with age at the three prey densities but larvae fed wi th 0.1 rotifer ml(-1) showed lower ingestion rates. The specific oxygen upt ake increased from hatching up to 35-40 mu g dry weight; above this size th e specific oxygen consumption remained almost constant. Survival at the end of the experimental period was closely related to the percentage of larvae able to start feeding at day 6. In larvae fed with 0.1 rotifer ml(-1), the energy ingested during the first days of feeding roughly met maintenance r equirements. Therefore, the survival of larvae able to start feeding is not guaranteed at such low prey density. (C) 2000 Elsevier Science B.V. All ri ghts reserved.