| | In their natural environment, trochus move across reef surfaces to forage on organic detritus and a variety of species of coralline and fleshy algae. They scrape these foods off the reef surface using a toothed 'radula' structure in their mouth. Trochus have been shown to prefer soft filamentous algae rather than leathery brown algae (Nash, 1985, Lee & Lynch, 1997). For aquaculture, benthic diatoms (single-celled micro-algae) such as Navicula spp . and Nitzschia closterium are grown on coral rubble or shell grit for trochus to feed upon. These can be supplied in small vials by CSIRO in Hobart or the University of Northern Territory, Darwin and scaled up to 20 L for inoculating the culture tanks. Recent methods on commercial production of micro-algae for feeding aquaculture species in marine hatcheries are given in Fulks and Main (1991). Husbandry and Health Status Diseases and parasites do not appear to be a problem in the culture of trochus, although little research has been conducted. In the wild, trochus shells can be damaged by a variety of invertebrate animals that bore into the shell, lowering the quality for sale. These parasitic and commensal organisms include copepods, vermetid gastropods, limpets, boring sponges and boring bivalves (Nash, 1993). The prevalence of shell damage by these boring animals increases with age of the animal and appears to differ among reefs and regions. Juvenile trochus released onto reefs for ranching are susceptible to predation, mainly by fish, mantis shrimp, crabs and octopus. Indeed, survival rates of small juveniles placed on reefs can be very low. This is a major impediment to achieving high returns from reseeding with hatchery produced juvenile trochus for stock enhancement. Research in Vanuatu, Indonesia, and King Sound, WA, however, has shown that intermediate culture of juveniles in cages (to protect them from predators) on the reef is promising, to a size of (30 - 40 mm). At 40 mm they are less vulnerable to predation after release from the cages. Robust cages are needed for these shallow reef sites (Purcell, submitted). | |