Abstract

Food web structure of the freshwater crayfish marron (Cherax tenuimanus) in aquaculture ponds and wild-stocks is pivotal knowledge for the understanding and successful management of the species. Food supplied to ponds should be targeted to maximise growth. Food that is not used to elaborate body tissue and for metabolism, represents both an economic and environment cost. In this study, multiple stable isotope analyses (carbon and nitrogen) were used to assess both the food web structure and relative trophic position of marron in aquaculture ponds. Marron have the ability to assimilate carbon from different sources. In ponds the signature of marron differed from the wild-stock. Marron fed commercial foods showed a high fidelity to the specific source of carbon (~-22 ppt). However the main additive to the ponds was pellets with a signature of ~-12 ppt (grains) which indicates a minor use of the whole pellet. Other primary sources of carbon such as leaves (~-27 ppt) and algae (~-38 ppt) indicate that marron are either mixing sources or concentrating on a specific source with a value of ~-22 ppt. Fish meal, a minor component of pelleted food, has the value of ~-22 ppt. The wild-stock showed values indicating substantial incorporation of C3 carbon (~-27 ppt) derived from the dominant riparian vegetation type of these streams. Larger marron of the same cohort tended to show elevated del-N values indicating they were relatively elevated in trophic position; therefore increasingly predaceous and may provide an insight into the cohort size distribution and average size at harvest. Stable isotope analysis is a useful methodology and can be developed further to target pellets for a more sustainable aquaculture industry and for the management of wild-stocks.

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