FISHERY BULLETIN: VOL. 87, NO. 3, 1989 



Figure 3. — Cylindrical larval and postlarval rearing tank. Vortical drive 

 airlift circulated tank in its simplest form. Tank is self-cleaning and vertical 

 extension for air-lift pipe allows foam fractionation (from Leighton 1965 

 (unpubl. data), 1977). a. Airline; b. air stone at base of airlift column; c. 

 drain port, normally closed; d. vortex; e. central stand pipe, removable; f. 

 return flow. 



Gravid adult abalone may be induced to spawn 

 using several different methods. Thermal shock, 

 still used in some hatcheries in Japan (Ino 

 1980), was initially used in U.S. abalone culture, 

 but soon abandoned in favor of the method of 

 Kikuchi and Uki (1974) using UV-irradiated sea- 

 water. Also available is the hydrogen peroxide 

 method developed by Morse and associates 

 (Morse et al. 1977, 1978). Each approach has its 

 advantages and disadvantages (Ebert and Houk 

 1984; Leighton and Lewis 1982). Usually brood- 

 stock are spawned in separate containers, then 

 gametes are collected and combined to yield the 

 highest fertilization rates. Eggs are subse- 

 quently washed and incubated under static con- 

 ditions at temperatures most appropriate for the 

 species (Leighton 1972, 1974). 



Embryos generally hatch from eggs in 12-18 

 hours as trochophore larvae. Soon after hatch- 

 ing, larvae display a negative geota.\is (Leighton 

 1972, 1974), swimming at the surface in culture 

 containers for (5-12 hours. This behavior, com- 

 mon to red, green, pink, and white abalones, has 

 been mistakenly regarded as a positive photo- 

 taxis in observations with H. rufescens by some 

 workers (c.f., Ebert and Houk 1984; Hooker and 

 Morse 1985). Light, however, has a negligible 

 influence on the swimming behavior of these 

 species in the trochophore and pre-eyespot 

 veliger larval stages. Larvae then become in- 

 creasingly demersal with age. Culture routines, 

 involving water changes and concentration of 

 larvae, take advantage of these behavioral char- 

 acteristics. 



In the hatchery, larvae are generally reared 

 through swimming stages (approximately one 

 week) in culture containers of small volume (5-10 



L) with careful attention to water quality, bac- 

 terial contaminants, temperature, and density. 

 Highly filtered (ca. 1 jjtm) seawater, antibiotic 

 treatment, and daily water changes promote 

 maximum survival (virtually 100%) and normal 

 development when larvae are incubated at den- 

 sities of 2 individuals/mL or less (Leighton 1977). 

 Some laboratories utihze mesh-bottom plastic 

 cylinders immersed in a highly controlled, circu- 

 lating system similar to that employed in bivalve 

 culture (Ebert and Houk 1984). 



The temperature dependency of early devel- 

 opment for the principal California species is 

 described by Leighton (1972, 1974). Cold-water 

 species (red, pinto, flat, and white) have thermal 

 optima for larval development in the range of 

 12°-16°C. The black abalone, while broadly toler- 

 ant of temperature in adult stages, is similar to 

 the cold-water species in larval life (optimum 

 14°-18°C; Leighton 1987). The green abalone is 

 distinctive, having a thermal optimum for larval 

 development in the range of 18°-24°C (Leighton 

 1974, 1985; Leighton et al. 1981). The pink aba- 

 lone is intermediate in its thermal requirements. 

 In contradiction to a recent report by Hooker 

 and Morse (1985), only the green abalone among 

 California species may be considered "thermo- 

 philic". Hatcheries involved in culture of red, 

 pink, and green abalones must observe the tem- 

 perature requirements of these species closely. 



Advanced larvae are induced to settle and 

 begin metamorphosis using a variety of methods 

 (see Problem Areas). Commonly, larvae at an 

 age of about six days are admitted to small vol- 

 ume tanks supporting thin coatings of benthic 

 microflora (chiefly diatoms and associated bac- 

 teria) wherein larvae settle within several hours 



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