FISHERY BULLETIN: VOL. 72, NO. 4 



were initiated with newly hatched trochophore 

 larvae. Trochophores normally hatched from eggs 

 at 15°-18°C within 12 to 18 h. Shortly after hatch- 

 ing, larvae swim to the surface ( negative geotaxis) 

 and are easily drawn into a pipette for transfer to 

 experimental containers. 



Thermal influence on development and survival 

 of larvae and postlarvae was observed using a 

 temperature gradient apparatus; an aluminum 

 block (30 X 15 X 150 cm) bored to accommodate 

 replicate series of test tubes (25 ml). Cooling coils 

 and heating elements at opposite ends maintained 

 a temperature differential (range: 7°-31°C) with 

 but slight fluctuation (±0.5°C per gradient posi- 

 tion) over the course of the average experiment 

 (2-4 wk). The apparatus is similar to that used 

 with H. sorenseni larvae (Leighton, 1972) and has 

 been thoroughly described elsewhere (Thomas, 

 Scotten, and Bradshaw, 1963). 



In the typical experiment duplicate series of 10 

 tubes, each tube containing 20 ml of seawater, 

 were placed in the thermal gradient with 50 eggs 

 or larvae. Incubation was carried out in darkness. 

 A foam urethane cover insulated the apparatus. 

 Inspection of the tubes was made daily during the 

 first week and on alternate days thereafter to de- 

 termine the stage of development attained. As 

 abalone larvae are lecithotrophic, feeding was not 

 necessary until settlement. At that time a mixture 

 of three species of pennate diatoms (Nitzschia 

 spp.) was supplied. 



Studies on postlarvae were also conducted using 

 the temperature gradient block. Between two and 

 five individuals were placed in each tube. Postlar- 

 vae 1-2 mo of age were picked individually from 

 walls of culture containers (Pyrex beakers or 

 polyethylene pails) using a finely bevelled ap- 

 plicator stick. Several drops of the diatom culture 

 were added to each tube twice weekly over the 

 usual 2-wk observation period. 



To examine the effect of temperature on the 

 success of juveniles, groups of 8-12 individuals 

 were reared in six 10-liter polyethylene contain- 

 ers maintained at 12°, 15°, 18°, 21°, 24°, and 27°C 

 (±1.0°). Water was continuously aerated and the 

 entire volume exchanged once a week. Food was 

 either a mixture of unicellular and filamentous 

 algae cultured within each container under il- 

 lumination of a fluorescent lamp or fronds of the 

 brown alga, Egregia laevigata, collected in fresh 

 condition every 3-4 days. Growth of juvenile 

 abalones was measured for month-long intervals 

 in these experiments. 



Progeny of each spawning were maintained in 

 the laboratory for over 1 yr providing comparative 

 information on juvenile growth rate in aquaria. 

 Diatoms and minute filamentous algae served as 

 food during their first few months. Older juveniles 

 were provided larger algae, Egregia laevigata, 

 Eisenia arborea, Macrocystis pyrifera, and 

 Laminaria farlowii. 



DEVELOPMENTAL FEATURES OF 



LARVAE, POSTLARVAE, AND 



JUVENILES 



While morphogenesis is gradual and does not 

 progress in a stepwise manner, various stages of 

 larval and postlarval development are recogniz- 

 able. Development rate was measured in terms of 

 the time required for larvae to first gain features 

 distinctive to each stage. Eleven such stages are 

 passed from trochophore larva to circular-shelled 

 postlarva (Figure 1). Settlement (the crawling 

 stage) marks the end of larval life. Postlarval de- 

 velopment then begins with the deposition of 

 peristomial shell and persists to formation of the 

 first respiratory pore ("notch stage," Leighton, 

 1972) at an age of 1-3 mo. Thenceforth to first 

 sexual maturity the abalone may be regarded as 

 juvenile. 



Figure 1.— 1) Trochophore larva after hatching. 2) Cap-shell 

 early veliger larva. 3) Inflate-shell veliger (torsion stage). 4) 

 Early operculate veliger (preeye spot). 5) Incipient cephalic ten- 

 tacle stage operculate veliger. 6) Midformed cephalic tentacle 

 stage. 7) Digitate or branched cephalic tentacle stage. 8) Crawl- 

 ing and settling stage. 9) Peristomial shell stage postlarva. 10) 

 Midasymmetric shell postlarva. 11) Circular-shell postlarva. 



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