School of Engineering

Projects

Sea cucumber biology and aquaculture

This study aims to investigate optimum growing conditions of sea cucumbers in semi-closed re-circulating aquaculture system and will address issues such as the effects of tank design, substrate depth, particle size on growth and behaviour of sandfish reared intensively in an experimental re-circulating aquaculture system via a factorial design.

Background

Sea cucumbers, once dried and processed into bêche-de-mer, are a high value niche product in the East. Global sea cucumber stocks are severely depleted and aquaculture is considered the only viable means of bridging the gap between supply and demand in the future. The sea cucumber Holothuria scabra is a commercially valuable aquaculture species; however viable intensive tank-based aquaculture techniques have not yet been developed.

Holothuria scabra, is considered as the best candidate species for sea cucumber aquaculture in the tropics. As deposit feeders adapted to processes large quantities of nutritionally poor sediment, sandfish are an ideal species for extensive forms of aquaculture in the natural environment. Stemming from the successful development of hatchery and nursery technology, sandfish is now the predominant species in sea ranching and sea farming programmes from Madagascar to Fiji.

Growth of sandfish is density-dependant and yields for current sandfish production models, range from 2.5 tonnes per hectare for sea ranching programs to 2.8 tonnes per hectare for pond culture. Provision of formulated diets to increase growth rates and permit higher stocking densities is a pre-requisite for intensification of sandfish aquaculture. Despite growing interest from the commercial sector, intensive culture techniques have not been developed for this species, although a number of studies have shown that sandfish grow well on commercially available formulated diets such as prawn starter and abalone feeds.

Project approach

One of the first steps in the development of intensive tank based technology is to determine the optimum tank holding conditions and substrate requirements for sandfish. While it seems clear that sandfish require sand, maintenance of optimum substrate conditions in culture tanks is considered to be one of the main barriers to intensification of production.

As the current research is undertaken in a semi-closed re-circulating aquaculture system consisting of a sand filter, protein skimmer and biological filter, the main objective was not to create an ‘in-tank’ sediment-based biological filtration, but rather to adapt the plenum-based design to prevent the development of anoxic sediment. An airlift pump was connected to the plenum to transport water from the void beneath the plenum up into the water column, creating a circulation of oxygenated water through the sediment. It was hypothesised that the active circulation of water through the substrate would alleviate problems associated with feeding a formulated diet, prevent the formation of reducing conditions and thereby permit increased feeding rates and higher stocking densities of sandfish in culture tanks.