Developmental stages and potential mariculture for coastal rehabilitation of endangered Pacific angelwing clam, Pholas orientalis

Abstract

Sexually mature Pacific angelwing clams, Pholas orientalis, were collected from the wild and spawned and cultured under laboratory conditions to document early developmental stages and to develop culture techniques for coastal rehabilitation of this endangered species. There was a highly significant difference ( P < 0.01) found in induced spawning of P. orientalis using desiccation method compared with those that were not desiccated. Depending upon the size, spawners released between 1 and 2 million eggs. Wild spawners used in this study were functional simultaneous hermaphrodites that self-fertilized their own eggs (43.0 ± 0.8 μm diameter). First cellular division and motile morula occurred after 46 min and 3 h, respectively. Actively swimming early veliger and crawling pediveliger stages emerged after about 15 h and 22 h, respectively. Approximately 99.7% of straight-hinge larvae (58.3 ± 0.3 μm shell length) appeared after about 23 h. Fed with Isochrysis galbana, Chaetoceros calcitrans, and Nannochloropsis sp., the average survival rate at umbo stage (128 μm shell length; 115 μm shell width) after 10 days was 92% at 30.0 ± 1.0‰ salinity, pH 8.04–8.15 and temperature 23.5–29 °C. Survival rate of juveniles (1.046 mm shell length; 0.701 mm shell width) in muddy substrate after 30 days post-spawning was about 16%. This is the first time that P. orientalis has been successfully spawned in captivity and reared through early embryonic, larval, and juvenile stages. Postlarvae of P. orientalis were successfully introduced in the muddy cove of San Dionisio, Panay Island, Philippines (11°13′N, 123°04′E) and have produced successive generations that successfully colonized the area. Coastal rehabilitation and mariculture using hatchery-produced seedstock of this species show very encouraging results.