MARINE ECOLOGY - PROGRESS SERIES Mar. Ecol. Prog. Ser. Published October 15 Combined Effects of Prey Concentration and Photoperiod on Survival and Growth of Larval Sea Bream, Archosargus rhomboidalis (Sparidae) C. E. Dowd and E. D. Houde Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami. Florida 33149, USA ABSTRACT: Effects of prey concentrations and photoperiods on sunrival and growth of larval sea bream Archosargus rhomboidalis (Sparidae) were determined in laboratory experiments. Larvae were reared from eggs to 16 d after hatching on copepod nauplii at 25. 50, 100 or 500 1-' combined with photoperiods of 7, 13 or 19 h light. Survival was highest at 13 h light duration and increased as the prey level was raised. Growth was best at 13 h light when prey concentrations were 100 or 500 1-l, but was best at 19 h light when prey concentrations were 25 or 50 1-' At high prey levels the larvae survived and grew best at ambient light durations; at low prey levels they benefited in growth, but not in survival, from a longer than normal photoperiod. INTRODUCTION field, were estimated by Ivlev (1960) and Blaxter (1966). Laurence (1977), using data on the number of Year-class size in marine fishes is determined in hours of light available and food requirements of lar- large part by mortality during the larval stage (Hunter, vae, predicted limiting prey concentrations for winter 1976) when food availability is an important factor flounder Pseudopleuronectes americanus. Laboratory (Cushing, 1975). Effects of food availability on larval experiments to determine effects of light intensity and growth and survival have been examined in laboratory photoperiod on larval fish growth and survival were and field experiments (Lasker, 1975; Houde, 1978; reported by Barahona-Fernandes (1979) on sea bass Houde and Taniguchi, 1979).Because larval fishes are Dicentrarchus labrax and Kiyono and Hirano (in press) visual feeders and cannot feed at most night light on black porgy Mylio macrocephalus. The effect of levels (Blaxter, 1966, 1968a, 1968b),their growth and photoperiod on growth and survival of sole larvae was survival may be lim~ted by the daylight hours avail- examined by Fuchs (1978). able for feeding as well as by prey availability (Blaxter, Objectives of our research were (1) to examine the 1966). In a laboratory study we have examined effects effect of length of photoperiod on growth and survival of photoperiod and prey concentration on growth and of larval Archosargus rhomboidalis, and (2) to deter- survival of larval sea bream Archosargus rhomboidalis. mine whether required prey concentrations differed in Some aspects of the role of light in larval fish ecology relation to length of photoperiod. have been investigated. The structure of the eye of larval plaice Pleuronectes platessa and sole Solea solea, larval responses to visual stimuli and the role of METHODS light in vertical migration were investigated by Blaxter (1968a, b, 1969, 1972, 1973, 1974). Light, its uses and Fertilized eggs of Archosargus rhomboidalis (family role in successful larval fish culture have been Sparidae) were collected in l-m diameter plankton reviewed in 'Marine Ecology', Volume I11 by Kinne nets in Biscayne Bay, Florida (USA) and stocked in 76-1 (1977),and the responses of fishes to light, in 'Marine rectangular tanks at a density of 2 1-l. Rearing proce- Ecology', Volume I by Blaxter (1970).The number of dures were similar to those described by Houde (1978). daylight hours required for adequate feeding by larval Water temperatures were maintained at 26 "C k 1 C" herring Clupea harengus, given the estimated food and phytoplankton blooms of Anacystis sp, and requirements and average prey concentration in the Chlorella sp. were added as a water conditioner. Vari- O by Inter-Research