Finfish production in a static, inland saline water body using a Semi-Intensive Floating Tank System (SIFTS)

Using a newly developed culture technology known as the Semi-Intensive Floating Tank System (SIFTS), rainbow trout (Oncorhynchus mykiss), mulloway (Argyrosomus japonicus) and barramundi (Lates calcarifer) were produced in a 0.13 ha static, inland saline water body over a period of 292 days, yielding the equivalent of 26 tonnes/(ha year). Rainbow trout were grown with an FCR of 0.97 from 83 to 697 g over 111 days (specific growth rate (SGR), 1.91%/day) between June and September, when average daily water temperatures ranged from 12.3 to 18.2 °C. Over the same time period, mulloway grew only from 100 to 116 g, however, once temperatures increased to approximately 21 °C in October, food intake increased and mulloway grew to an average size of 384 g over 174 days with an SGR and FCR of 0.68%/day and 1.39, respectively. Barramundi stocked in November with an average weight of 40 g increased to 435 g in 138 days (SGR 1.73%/day) with an FCR of 0.90. The SIFTS significantly reduced nutrient input into the pond by removing settleable wastes as a thick sludge with a dry matter content of 5–10%. The total quantity of dry waste removed over the culture period was 527 kg (5 tonnes/(ha year)), which was calculated to contain 15 kg of nitrogen (144 kg/(ha year)) and 16 kg of phosphorus (153 kg/(ha year)). The release of soluble nutrients into the pond resulted in blooms of macro- and micro-algae which caused large and potentially lethal diurnal fluctuations in dissolved oxygen within the pond, however, comparatively stable levels of dissolved oxygen were maintained within each SIFT1 through the use of air lift pumps

Factors affecting mark quality of alizarin complexone-stained otoliths in juvenile black bream Acanthopagrus butcheri and a prescription for dosage

The relationships between otolith score, a function of increasing stain visibility, and the ratio of alizarin complexone (mg) to fish biomass (g) for 0·1, 0·6 and 7 g black bream Acanthopagrus butcheri show that acceptable marks are produced in all size classes using a stain-to-biomass ratio of 3·3 mg g-1 following an immersion period of 24 h

Development of techniques for the collection and culture of wild-caught fertilised snapper (Chrysophrys auratus) eggs for stock enhancement purposes

Restocking or stock enhancement programs have traditionally relied on captive broodstock to produce individuals for release into the wild. However, this is costly and may limit genetic diversity of the resulting progeny. If fertilised eggs could be collected from the wild and individuals reared for release, the genetic diversity of the released progeny may be improved and associated restocking/enhancement programs may become more cost-effective. Snapper (Chrysophrys auratus: Sparidae), is an iconic recreational and commercial fish species across Australia and New Zealand and has been subjected to overfishing in many locations. Enhancement programs may be useful for increasing biomass in some circumstances, but would require careful evaluation of advantages and disadvantages before commencement. This study developed and optimised egg collection methods for snapper from its wild spawning aggregations in Cockburn Sound, Western Australia, and developed effective otolith marking techniques that would enable future monitoring of released individuals. The study identified the optimum sea conditions for collecting large numbers >100,000) of eggs using plankton nets, in addition to the need for side-scan sonar to locate spawning aggregations, the distance from aggregations at which to sample and the water depth for plankton net tows. Large numbers of eggs collected in 2014 and 2015 were subsampled and visually screened for presence of snapper eggs using known egg diameters. Real-time PCR techniques validated visual identifications of snapper eggs and larvae, limiting accidental rearing of non-target species and reducing associated costs. Trials on larvae reared from these eggs, successfully determined appropriate alizarin complexone concentrations and immersion times for producing enduring marks on post-larvae otoliths. These marks remained visible in otoliths after 12 months, potentially allowing future monitoring of fish released into the wild. Delayed disinfection of eggs to the second day after capture resulted in improved egg viability. Following optimisation of collection and culture techniques, 208,000 larvae were stocked from a single sampling occasion in 2015, of which 19% survived to 55. days post hatch (dph). This survival rate is typical for snapper produced from captive broodstock. This study demonstrated that wild spawned snapper eggs can be captured and cultured in high numbers and future identification of recaptured released fish potentially conducted. An associated genetic study also demonstrated no loss of genetic diversity in cultured fish versus that of adults in the spawning aggregations. This technique has the potential to reduce both the cost of restocking/stock enhancement programs for snapper (and could be evaluated for other suitable aggregating species) and the risks of altering the genetic makeup of wild stocks