Improving Profitability to Industry Through the Identification and Management of 'tough' Fish Syndrome in Tropical Saddletail Snapper (Lutjanus Malabaricus)

OBJECTIVES: 1. To determine whether incomplete rigor mortis resolution and 'cold shock' play a role in development of tough fish syndrome (TFS) in tropical Saddletail snapper. 2. To identify links between TFS and specific physiological factors in tropical Saddletail snapper. 3. Communicate findings and recommendations to stakeholders and assist with implementation of any changes to fishing or handling practices required

Streptophage-mediated control of off-flavour taint producing streptomycetes isolated from barramundi ponds

Off-flavour taint of aquaculture products is a global issue reducing consumer confidence in the farmed produce as they are taken up via the gills of fish, and deposited in the lipids of the animal. If the fish are not purged, resulting undesirable muddy earthy flavour taint can be tasted by consumers. These undesirable flavour and odour is caused by the terpenoid compounds namely geosmin and 2-methylisoborneol, produced as secondary metabolites by certain bacteria including the cyanobacteria and actinomycetes. Current strategies to remediate the problem rely on treating the symptoms not the cause and involve the use of time consuming purging methods and costly chemicals. Biological control using bacteriophages, specific to the problem causing bacteria, offers a natural alternative to chemical control, which might reduce further complications of copper based algaecides and its subsequent implications on water quality. In an adaptation of such biological control approach streptomycetes isolated from barramundi ponds were tested for their susceptibility to streptophages to understand whether host destruction via phage lysis would subsequently eliminate off-flavour taint productions by these isolates. Following the determination of the streptophage susceptibility of the isolates one of the most odourous streptomycete species (USC-14510) was selected to be tested further using different pond simulations resembling real-life applications. Geosmin was tested as the indicator of off-flavour taint production and as it has been previously reported that the cyanobacteria-actinomycete interactions occurring in ponds result in even greater levels of geosmin and 2-methylisoborneol, the geosmin levels for the isolate in the presence of cyanobacteria and streptophages were also tested. Findings indicated that the highly odourous Streptomyces species (USC-14510) once infected with streptophages, can lose its capacity to produce off-flavour taints. Pond simulation studies also revealed geosmin production was significantly reduced when streptophages were introduced into the pond water where streptomycete species were grown. The bacteriophage control method developed in the presented study might again confirm significant potential for the bacteriophage-mediated remediation strategy to be adapted by the aquaculture industry

Astaxanthin profiles and corresponding colour properties in Australian farmed black tiger prawn (Penaeus monodon) during frozen storage

The colour of commercial cooked black tiger prawns (Penaeus monodon) is a key quality requirement to ensure product is not rejected in wholesale markets. The colour, due to the carotenoid astaxanthin, can be impacted by frozen storage, but changes in colour or astaxanthin profile, during frozen storage, have not been studied in detail. Subsequently in this study, the aims were to define the astaxanthin (as cis, trans, mono-ester and di-ester forms) content, together with the colour properties, in both pleopods (legs) and abdominal segments. Changes in astaxanthin content and colour properties were further determined during frozen storage (−20°C). Total astaxanthin content was seen to decrease in all samples over time, with the rate of degradation being significantly greater (P < 0.05) in pleopods than abdomen. In both pleopods and abdomen, rate of degradation of esterified forms was significantly greater (P < 0.05) than non-esterified forms. Hue angle (increase), a* value (decrease) and L value (increase) were all seen to significantly change (P < 0.05) during storage, with changes being more prevalent in the pleopods. The pleopods are the key indicator of astaxanthin and colour loss in cooked black tiger prawns and preservation strategies are required to preserve astaxanthin and colour during frozen storage

A novel method for the age estimation of Saddletail snapper (Lutjanus malabaricus) using Fourier Transform-near infrared (FT-NIR) spectroscopy

Near infrared (NIR) spectroscopy was investigated as a potential rapid method of estimating fish age from whole otoliths of Saddletail snapper (Lutjanus malabaricus). Whole otoliths from 209 Saddletail snapper were extracted and the NIR spectral characteristics were acquired over a spectral range of 800–2780 nm. Partial least-squares models (PLS) were developed from the diffuse reflectance spectra and reference-validated age estimates (based on traditional sectioned otolith increments) to predict age for independent otolith samples. Predictive models developed for a specific season and geographical location performed poorly against a different season and geographical location. However, overall PLS regression statistics for predicting a combined population incorporating both geographic location and season variables were: coefficient of determination (R2) = 0.94, root mean square error of prediction (RMSEP) = 1.54 for age estimation, indicating that Saddletail age could be predicted within 1.5 increment counts. This level of accuracy suggests the method warrants further development for Saddletail snapper and may have potential for other fish species. A rapid method of fish age estimation could have the potential to reduce greatly both costs of time and materials in the assessment and management of commercial fisheries