Naga, The ICLARM Quarterly (Vol. 23, No. 2) April-June 2000 18 Introduction The tropical marine anemone- fishes (Pomacentridae) are important in the trade for ornamental fish (Wilkerson 1998) and are a popular subject of research (Fautin 1991). Over the last 20 years, mariculture centers and scientific laboratories have started rearing these fishes in large quantities (McLarney 1985, 1986; Miyagawa 1989; Hoff 1993; Young 1996; Job et al. 1997). The list of marine fishes reared in cap- tivity today, for purposes other than human consumption, contains more than 84 species (Tables 1 and 2). The fact that 26 different species from the family Pomacentridae are reported to be reared is notable. This is a sig- nificantly higher number of species compared to all other families. How- ever, when we look at species that can be reared reliably in large quan- tities, they include only a dozen anemonefish species, seven species of gobiids (Gobiidae), five species of cardinalfishes (Apogonidae) and eight species of pseudochromids (Pseudochromidae) The last two are only included here as a result of re- cent work by Gardner (1997) and Job et al. (1997). For all the species within the families mentioned above, larval rearing is still time-con- suming and expensive. This paper describes the growth experiments conducted at the Sir George Fisher Research Aquarium, James Cook University (JCU), to im- prove the methods for rearing anemonefishes so as to reduce the time and cost of rearing them for sci- entific studies. Only two studies have experi- mented with ways of enhancing the efficiency of larval rearing of anemonefishes. Frakes and Hoff (1982) published a study on the ef- fect of high nitrate-N on the growth and survival of juvenile and larval anemonefish A. ocellaris. Alayse (1984) studied the survival rate of A. ocellaris larvae fed on enriched food. This study examines the growth rates of larvae and juveniles under different light regimes. This variable is important as anemonefish larvae are visual feeders (Coughlin 1994; Job and Bellwood 1996). Sci- entists have shown that an extended photoperiod can significantly in- crease the growth rate of the larvae and early juveniles of a variety of marine fish species (Fuchs 1978; Barahona-Fernandes 1979; Boehlert 1981; Kiyonon and Hirano 1981; Tandler and Helps 1985; Duray and Kohno 1988; Barlow et al. 1995). Hoff (1996) and Wilkerson (1998) estimate the optimum growing con- ditions for anemonefish larvae to be a 16-hour daily light period, while Juhl (pers. comm.) recommends a 24- hour light regime. None of these au- thors present supporting data. This study investigates the effect of 12 hour, 16 hour and 24 hour photo- periods on the growth and larval duration of the anemonefish A. melanopus . Materials and Methods FISH MAINTENANCE AND REARING Breeding pairs of A. melanopus were collected from the Cairns sec- tion of the Great Barrier Reef and placed in 60-l tanks with gravel fil- ters and 200-l powerheads for the circulation of the water. Rocks were placed as a surface on which the fish could spawn. Water in the tanks was obtained from the JCU aquarium sys- tem. It had 33% salinity, 27-30°C tem- perature (daily variation, summer), 21-25°C (daily variation, winter) and a pH of 8.0-8.2. The water in the pa- rental tank was flushed daily with water from the main aquarium sys- tem. The JCU system is closed, with coastal water filtered through sand and large protein skimmers. Spawning occurred approximately every three weeks, and produced Effects of Photoperiod on Growth of Larvae and Juveniles of the Anemonefish Amphiprion melanopus M. Arvedlund, M.I. McCormick and T. Ainsworth Rearing of anemonefishes is now relatively routine compared to the culture of cardinalfishes (Apogonidae) or angelfishes (Pomacanthidae). However, it is still a labor intensive, time intensive and expensive procedure. To reduce time and cost of rearing anemonefishes, experiments were undertaken to improve the methods for rearing Amphiprion melanopus. These experiments were conducted to determine the effect of the length of photoperiod on larval duration, growth to metamorphosis and early juvenile phase. Growth of larvae was significantly faster and the duration of the larval phase was significantly shorter, under a photoperiod of 16 hours light/8 hours dark, compared to the photoperiods of 12 hours light/12 hours dark and 24 hours light/0 hours dark. Abstract