The Tasmanian salmonid industry has recently been faced with several significant production issues necessitating increased use of antibiotics and antifoulants. The effects of these chemicals on the local ecology and ecosystem function are currently poorly understood and without evidence to the contrary, it is difficult for the industry to refute the perception that such chemicals have a detrimental effect on the environment.

There is a large body of literature regarding the effects of antibiotics, however the information pertaining to aquaculture is limited. Improvements in husbandry and vaccine development have now all but eliminated the use of antibiotics in aquaculture overseas, consequently there have been few recent aquaculture specific studies, with even fewer studies on ecosystem effects, the available information largely focussing on environmental persistence and antibiotic resistance. However, there is quite a lot of information in the terrestrial livestock and medical areas on the comparative effects of various antibiotics as well as quite a substantial ecotoxicological literature. In contrast there is a substantial local literature on the environmental impacts of antifoulants and heavy metals. There is a need for a targeted review to establish environmental risk factors associated with current antibiotic and antifoulant usage and to develop an appropriate strategy to research and monitor ongoing impacts.

Some data on sediment residue levels for both antibiotics and antifoulants has been collected by the salmon industry in compliance with drug/chemical licensing permit conditions authorities and by the state government in response to concerns regarding antibiotic usage. So far this data has not been collated and has only been subjected to preliminary analysis; a comprehensive evaluation of this data would markedly improve our understanding of current impacts and help to determine what additional information may be required.

Blue swimmer crab (BSC) post-harvest flesh quality in Shark Bay WA is a concern to Abacus Fisheries. 10-20% of crab flesh is unsaleable (i.e. mushy) after cooking, equating to losses of between $250,000 and $500,000/year (Fishery value:$1.8-2.5M/yr).

Mushiness in BSC may be caused by proteolytic enzymes escaping from the hepatopancreas post-mortem and breaking down adjacent muscle tissue (Slattery et al 1989). This can occur if crabs die before cooking (Stevens, 1995) or cooking times are too short or temperatures too low. Slattery et al found that cooking temperatures of greater than 70oC for 10 minutes reduced the problem.

Notwithstanding the above, the problem persists in Shark Bay despite cooking torpid live crabs for 13 minutes at 95-97oC. This suggests further information is needed to resolve the issue. For example, muscle water content is highest in postmoult/early intermoult crustaceans (Musgrove, 2001), possibly contributing to mushiness on processing. Shark Bay crabs moult throughout the year although peaks appear around January/February, May/June and July/August (P. Jecks. pers. obs.).

Parasite infestation (i.e. microsporidians especially Ameson sp.) in harvested crabs may also result in mushy flesh after cooking (Shields and Overstreet, 2007). Stress may also affect tissue quality, influenced by predators (eg. octopus), harvest process, boat well overcrowding or sub-optimum post-harvest chilling. The effect of gut-fullness is also unknown; fuller guts may generate greater protease activity, leading to more postmortem tissue breakdown.

Abacus Fisheries has developed new markets and products, yielding significant premiums and substantial increases in BSC beach price. However, the occurrence of mushy flesh can slow production through excessive time spent checking for flesh quality. This impacts profitability and can threaten the super-premium fine dining market position enjoyed by Abacus Fisheries products. There is a need to clarify the causes of flesh deterioration so alternate harvesting or processing strategies can be implemented.