Understanding the ontogenetic changes in particle processing of the greenshellTM mussel, Perna canaliculus, in order to improve hatchery feeding practices

Abstract

Despite the commercial aquaculture importance of the GreenshellTM mussel, Perna canaliculus, the morphological development of gill structure (ctenidial filaments) in relation to potential particle feeding abilities have not been described. Scanning electron microscopy (SEM) and light microscopy were used to examine the ontogenetic changes across five size classes of mussels from post-settlement larvae to adults ranging from 300μm to >100mm in shell height. Key morphological characteristics were measured including filament width, the eulatero-frontal cirri (ELF) length, interfilamentary space (IFS) and the mean distance between adjacent ELF, dELF. Overall the development of the ctenidial filaments in P. canaliculus, shared some similarities to other homorhabdic filibranch bivalves with differences in the timing of development. Filament width and ELF length followed sigmoidal growth curves in relation to increasing shell height of mussels. The morphological changes of the ctenidia, reflected in changes in the ELF/IFS ratios, together with the development of cilia in the ELF may help explain the differences in the capture efficiency of small particles between small individuals (<6mm in shell height) and bigger mussels (around 60mm in shell height). Ctenidial filaments in small individuals are not fully developed and resemble the “leaking” model, letting small particles through and capturing particles between 15–25μm, while the filaments in bigger mussels resemble the “complete block” model being able to capture bacteria-sized particles around 2μm. This information is not only useful to further the understanding of the feeding biology of this species, but also for the feeding management in hatcheries producing large numbers of juveniles of this commercially important species, considering that under current hatchery practices small-sized mussels are being fed microalgal species mainly with a size of around 5μm.–This article provides information regarding the gill ontogenetic development of the commercially important GreenshellTM mussel, Perna canaliculus.–The information given will help improve hatchery practices, especially regarding the selection of adequate particle size for feeding post-settlement P. canaliculus.–Considering that mussel aquaculture is a global phenomenon, these results could be used worldwide in order to help the industry find economically feasible alternatives for mussel juvenile supply.The New Zealand GreenshellTM industry has recently invested $20M to build a large scale hatchery/nursery to address an on-going shortage with seed supply which has been constraining the growth of the industry. Shortages of mussel seed, caused by poor feeding and starvation, have resulted in seed shortages in the industry for the last three years, shaving off almost 20% production of the entire industry, in the order of $30M lost production a year. Hence there is intense interest in better understanding the feeding biology of juvenile mussels and using this knowledge to resolve the major production issues faced by this aquaculture industry. From our international contacts, we understand that other countries with significant mussel farming industries face similar issues, such as Chile. Therefore, we believe that there is strong reader interest and value in the publication of this fundamental research.