26 



ONTOGENY AND SYSTEMATICS OF FISHES-AHLSTROM SYMPOSIUM 



to consume and which may be larval predators. Fish larvae, 

 particularly yolk-sac stages, are vulnerable to various carnivo- 

 rous copepods, amphipods, euphausiids and chaetognaths 

 (Hunter, 1981). 



Cultured foods.— T-wo cultured foods, the rotifer Brachiomts 

 plicatilis, and nauplii of the brine shrimp, Arteinia. should be 

 considered as potential foods for rearing marine fish larvae as 

 many fish larvae can be reared on a combination of these two 

 foods. These two foods may also be used as a supplement to 

 diets of wild plankton. Groups of fishes that have been reared 

 to metamorphosis on a combination oi Brachionus and Anemia 

 or on Artemia alone include C. harengns, species of serranids, 

 scombrids, atherinids, various flatfishes, sciaenids, and saganids 

 (May, 1970; May etal., 1974; and unpubl. SWFC data). /lr?ew;a 

 nauplii are recommended only for larvae with differentiated guts 

 as they are quite resistant to digestion whereas copepods are not 

 (Rosenthal, 1969). 



Methods for culturing rotifers using algae are given by Thei- 

 lacker and McMaster (1971); culture methods employing for- 

 mulated artificial diets or freeze dried algae (Gatesoupe and 

 Robin, 1981; Gatesoupe and Luquet, 1981) and ones using 

 brewers yeast also exist. Many of the essential facts given in 

 these original papers will not be repeated here but I will point 

 out a few practical points regarding rotifer culture using algae. 

 Suitable algae species for rotifer culture include Dunaliella, 

 Nannochloris, Tetraselmis, and Chlorella which may be grown 

 using standard culture media (Guillard, 1975) or using liquid 

 commercial plant fertilizers (dosage for fertilizer containing 8% 

 total nitrogen = 0. 1 ml of fertilizer/1; dosage among brands is 

 adjusted depending on total N content). We prefer commercial 

 plant fertilizers that have an organic base such as liquid fish 

 fertilizers and avoid those that have soil penetrants. A daily 

 doubling rate can be expected in healthy rotifer cultures, and 

 cultures can be maintained for weeks or even months by adding 

 fresh algae or nutrients and sea water, although single batch 

 harvesting after about 2 weeks gives more dependable results. 

 Rotifers are harvested using gravity flow through a nylon filter 

 (20-40 ^m mesh) as pumps may kill rotifers. 



Production ofArlemia nauplii is simple since all that is needed 

 is to hatch the cysts ("Anemia eggs"). Cysts from a variety of 

 strains of Anemia are commercially available. The strains differ 

 considerably in average naupliar size (423-775 ^m length), in 

 pesticide content (DDT, PCB, and chlordane) and in certain 

 fatty acids (Klein-MacPhee et al., 1982). These authors show 

 that very low survival (15%) of P. amehcanus larvae occurred 

 when they were fed San Pablo Bay (San Francisco) nauplii 

 whereas survival of larvae fed other strains varied from 60- 

 80%. Beck et al. ( 1 980) gave similar results for Menidia menidia 

 larvae. Of all the strains tested in these papers the Australian 

 and Brazilian strains seem the most suitable for rearing larvae 

 and the San Pablo Bay (USA) the least. - 



Anemia hatcheries vary from a jar to complex automated 

 systems. The J. D. Riley Anemia hatching box has been used 

 with slight modification in many laboratories for over 20 years. 

 It is a sea water filled box separated in half by a sliding partition; 

 Anemia cysts are added to one side (I g/l) and they hatch 1-2 



^ Exotic Anemia cysts are available from: Artemia Inc., P.O. Box 

 2891, Castro Valley, California 94546 USA and Biomarine Research. 

 4643 W. Rosecrans, Hawthorne, California 90250 USA. 



days later depending on the temperature selected (23-30° C). 

 The tank is then illuminated, the partition raised slightly off the 

 bottom, and the nauplii, attracted by the light, swim beneath 

 the partition leaving behind the hatching debris and unhatched 

 cysts (Shelboume, 1964). A semiautomatic version of this sys- 

 tem is described by Nash (1973), and various other improve- 

 ments in aeration, illumination, temperature, and other factors 

 have increased yields to lO' nauplii per 4.8 g of cysts (San 

 Francisco Bay Brand) (Dye, 1 980). In recent years decapsulation 

 of Anemia cysts using hypochlorite bleach has become popular 

 because it increases yields, increases the dry weight of the nau- 

 plius (Bruggeman et al., 1 980) and eliminates contamination of 

 larval fish rearing tanks with unhatched cysts. 



It should also be noted that freshly hatched Anemia nauplii 

 are clearly more nutritious than older starving individuals and 

 consequently new batches should be frequently produced. In 

 general, prey with full stomachs are probably nutritionally pref- 

 erable to ones with empty stomachs. Similarly, more Dicen- 

 trarchits labrax larvae seem to survive when rotifers are nutri- 

 tionally enhanced by 30 min immersion in a solution containing 

 vitamins and soluble proteins (Gatesoupe and Luquet, 1981). 



Mass culture of marine copepods is difficult and laborious 

 and therefore not recommended when a taxonomic series is the 

 sole objective. Nevertheless, culture of marine copepods may 

 be the only way some fish larvae can be reared if wild zooplank- 

 ton is not readily available and larvae die when fed Anemia 

 nauplii (rarely are more than a single strain of Anemia tested, 

 however). Harpacticoid copepods (Tignopus sp., Tishe sp., and 

 Euterpina sp.) are the most frequently used copepods because 

 of ease of culture; for culture techniques see Kahan et al. (1982) 

 and Hunter (1976). Euterpina may be preferable to Tignopus 

 or Tishe because the nauplii and copepodites of Euterpina are 

 pelagic and therefore available to the larvae whereas nauplii and 

 copepodites of Tigriopus and Tishe tend to remain on surfaces 

 and are therefore less available (Kraul, 1983). See Nassogne 

 (1970) and Zurlini et al. (1978) for laboratory culture of Euter- 

 pina. 



Eood density. —The optimal food density for fish larvae depends 

 upon the size of the food organism and size or age of the larvae. 

 Densities of 1-3 organisms/ml have been routinely used for 

 larvae fed wild zooplankton (largely copepod nauplii) during 

 the first 1-2 weeks of feeding (Houde and Taniguchi, 1979). 

 The same density range is used when cultured .Anemia nauplii 

 are the food. A higher density range (IO-20/ml) is used for 

 cultured B. plicatilis which are about 1/10 of the weight of an 

 .irtemia nauplius (Theilacker and McMaster, 1971). A very 

 small food particle, the dinoflagellate Gymnodinium splendens 

 (40 nm dia), is used for the first 2 days of feeding in northern 

 anchovy larvae (Lasker et al., 1970; Hunter, 1976) at a high 

 density of about lOO/ml. In very active species such as S. ja- 

 ponicus or the siganid Siganus canaliculatus high food densities 

 can cause heavy mortality because of overfeeding since most 

 larval fishes seem to lack a satiation mechanism (May et al., 

 1974; Hunter, 1981). Overfeeding seems to occur only when 

 such easily captured prey as .irtemia nauplii are used as food. 



Piscivorous fish /arvac — Piscivorous fish larvae such as the 

 scombroids, Sphyraena and others pose special problems in 

 culture. Fish larvae are an ideal food for such larvae; in fact, 

 our only success in rearing Katsuwonus pelamis larvae to meta- 

 morphosis was probably related to an abundant supply of yolk- 



