Larval cultivation of Periglypta chemnitzii based on microalgal dietary selection

Abstract

Periglypta chemnitzii is an edible shellfish whose hardy nature makes it an ideal species for cultivation by aquaculture. The crucial factor determining whether a species is appropriate for aquaculture is successful breeding of the offspring. In this study, we gathered information regarding reproduction and larval cultivation of P. chemnitzii and assessed the suitability of different microalgae diets to serve as a baseline for the purpose of artificial breeding of the offspring. The embryonic and larval development, larval morphological changes, movement, and feeding behaviour of P. chemnitzii were observed under an optical microscope. Eight microalgal species (Chlorella vulgaris, Nannochloropsis oculata, Dunaliella salina, Platymonas subcordiformis, Pavlova viridis, Dicrateria zhanjianggensis, Isochrysis galbana, and Chaetoceros muelleri) were fed to the larvae at different ages to observe the ingestion and digestion by the larvae. Four kinds of single microalgae diets (C. vulgaris, P. subcordiformis, C. muelleri, and D. zhanjianggensis) and three kinds of mixed diets (P. subcordiformis + C. muelleri, P. subcordiformis + D. zhanjianggensis, and C. muelleri + D. zhanjianggensis) were fed to larvae respectively, and their growth and survival rate was monitored. We found that the fertilised eggs of P. chemnitzii hatched into D-shaped larvae after 11 h 26 min; the larvae then developed to the metamorphic stage at 6 days post hatch (dph) and began settlement at 7 dph. The larvae could ingest C. vulgaris, N. oculata, D. salina, P. viridis, D. zhanjianggensis, and I. galbana at 1 dph; some larvae could also ingest P. subcordiformis and C. muelleri at 2 dph. Notably, C. vulgaris and N. oculata were more difficult to digest. Further, mixed diets were more beneficial than single diets for larval growth and survival. In particular, the mixed combination of P. subcordiformis + C. muelleri afforded the fastest growth and the highest survival rate. In single diets, the fastest growth was attained with C. muelleri; whereas the highest survival rate was obtained with P. subcordiformis. Compared with other bivalve molluscs, the clam P. chemnitzii has larger embryos and larger-sized newly hatched larvae, and its embryonic development and planktonic larval stage are also shorter than that of other species. P. chemnitzii larvae were more likely to ingest the smaller, round-shaped microalgal species and digest the species without cell walls, and therefore, D. zhanjianggensis should be the first choice as an opening diet for P. chemnitzii larval cultivation, followed by a mixed microalgal diet of P. subcordiformis + C. muelleri from 3 dph onwards.