LEIGHTON: ABALONE MARICULTURE 



to two days. It was observed early in red abalone 

 hatchery research that larvae introduced to 

 tanks precolonized by crustose coralline red 

 algae settled promptly. Tanks which had re- 

 cently held healthy conspecific juveniles, the 

 walls of which presented a well-grazed micro- 

 floral substrate, proved especially beneficial to 

 successful settlement and metamorphosis 

 (Leighton 1987). Several sources of "inducers" 

 which effectively prompt settlement and meta- 

 morphosis appear to e.xist (see Problem Areas). 



Settled larvae immediately begin feeding on 

 bacteria and other microflora. Metamorphosis 

 commences with loss of the velar c'iia and larval 

 operculum. Deposition of peristomial shell is evi- 

 dent within another day, but metamorphosis is a 

 complex and gradual transition. The first respir- 

 atory pore is formed at the end of postlarval life 

 (onset of the early juvenile stage), generally as 

 the abalone reaches 1.5-2.5 mm (age about six 

 weeks). 



Postlarval attrition continues to remain as the 

 principal "efficiency bottleneck" in abalone cul- 

 ture. Under usual hatchery conditions, survival 

 and normal development for swimming larvae 

 are close to 100% (Leighton 1977, 1985), but 

 mortaUties occur in a large percentage of meta- 

 morphosing postlarvae vdth the result that early 

 juveniles represent at best 5-10% of the number 

 of larvae at settUng. Declines are most evident 

 during the fourth to sixth week postfertilization. 

 However, when conditions are optimized (us- 

 ually in small volume containers), survival 



through postlarval life may be over 25% (c.f., 

 Leighton et al. 1981; Table 1). Losses during 

 critical early benthic stages may thus be reduced 

 significantly by appropriate control and care to 

 include frequent water changes, maintenance of 

 clean conditions, and supplying microalgal foods 

 on a regular basis (see Problem Areas). 



Juvenile Culture 



Once postlarval abalone begin to form the first 

 respiratory pore, the pallial system (gills and 

 associated structures) and other features of 

 anatomy become more typical of the adult. The 

 juvenile stage commences at this point and ex- 

 tends to young adulthood and onset of sexual 

 maturity. Dietary changes occur in conjunction 

 with development; first-settled metamorphosing 

 postlarvae feed upon smaller microflora (dia- 

 toms, sessile flagellates, and bacteria). Early 

 juveniles rely on many larger microalgae, but 

 undergo a dietary transition to include a variety 

 of green, red, and brown macroalgae as ad- 

 vanced juvenile stages are approached. The diet- 

 ary transition to macroalgae occurs in many 

 species at about 1 cm shell length (4-6 months), 

 but is usually never complete as microalgal films 

 may be ingested and metabolized through adult 

 life (Leighton 1987). 



When juvenile abalone reach about 3 mm, they 

 are transferred to larger tanks precolonized by 

 appropriate algae. Transfer is achieved with 

 negligible losses by simple brushing (Leighton 



Table 1 . — Size increase for young adult red and green abalones provided two 

 brown algal diets. 



Mean shell length increases (|xm/d) for young adult abalone held in duplicate groups (6 

 individuals group) Abalone were fed to satiation throughout three feeding periods of 

 40-50 days each. All abalone were in the size range 5-10 cm; groups were held in 10 L 

 plastic pails receiving ambient seawater at 1 L'min and vigorous aeration To promote 

 continuous feeding, freshly collected algae were provided in excess (ca 100 g) weekly. 

 Haliotis rulescens observations were made in winter, 13°-17'C; H. fulgens in summer 

 and fall, 18°-22°C. 



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