Survivorship and growth of the sea cucumber Australostichopus (Stichopus) mollis (Hutton 1872) in polyculture trials with green-lipped mussel farms

The suitability of the common New Zealand sea cucumber Australostichopus mollis to polyculture with green-lipped mussels was investigated in a six-month field study. Sea cucumbers were caged at three densities (2.5, 5 and 15 ind m- 2) on the seabed beneath an operating mussel farm and survivorship and growth (weight change) monitored on a monthly basis. The sea cucumbers transplanted to below an operating farm showed excellent survivorship (91.7% overall) over the period of the study and exhibited growth at densities exceeding observed natural densities. Growth was density-dependent and at the highest densities appeared to be constrained by food limitation. A. mollis held at 2.5 and 5 ind m- 2 gained 15.37% ± 5.33 (mean ± SE) and 13.16% ± 3.42 of their pre-caged body weight, respectively, while those caged at a density of 15 ind m- 2 showed a 0.21% ± 2.12 weight loss over the six-month trial. In addition, the acceptability of mussel farm-impacted sediment as a food source was investigated in tank-based feeding experiments with wild-collected A. mollis. Adult A. mollis readily consumed mussel farm-impacted sediment in laboratory feeding experiments, consuming 6.70 g ± 1.59 (mean ± SE) wet weight mussel sediment d- 1. These results clearly indicate that A. mollis is an ideal candidate for polyculture with green-lipped mussel farms. © 2007 Elsevier B.V. All rights reserved

Effect of sea cucumber (Australostichopus mollis) grazing on coastal sediments impacted by mussel farm deposition

Deposit-feeding holothurians are important processors of surface sediments in many coastal marine systems. The present study examined the effect of grazing by the sea cucumber Australostichopus mollis on sediment impacted by green-lipped mussel biodeposits (faeces and pseudofaeces) from coastal aquaculture activities. Grazing effects were investigated in a series of tank-based feeding experiments conducted over 1, 2, 4 and 8 week periods. Sediment quality indicators routinely applied to determine the impacts of coastal aquaculture were used to evaluate sediment health from grazed and ungrazed sediments. Sea cucumber grazing resulted in reductions in total organic carbon, chlorophyll a and phaeopigment, as well as chlorophyll a/phaeopigment ratio of impacted sediments. These results demonstrate that sea cucumber grazing significantly reduces the accumulation of both organic carbon and phytopigments associated with biodeposition from mussel farms. Sea cucumber grazing offers a means of constraining or reversing the pollutive impacts of coastal bivalve aquaculture. © 2009 Elsevier Ltd. All rights reserved

Sea cucumber habitat differentiation and site retention as determined by intraspecific stable isotope variation

Stable carbon and nitrogen isotope ratios (δ13C/δ15N) were assessed as a means to ascertain the recent in situ feeding history of the common New Zealand sea cucumber Australostichopus mollis in relation to nutrient enrichment from a longline green-lipped mussel (Perna canaliculus) farm in Northern New Zealand. δ13C and δ15N isotopic signatures and the ratios of sea cucumbers sampled from within the impact footprint of the mussel farm were compared with those of sea cucumbers residing on adjacent natural reefs. Sea cucumbers from beneath mussel farming longlines had significantly different δ13C stable isotope signatures in comparison with sea cucumbers collected from neighbouring natural reef habitats. This difference supports the hypothesis that sea cucumbers in the same bay maintain distinctly different feeding histories, with those residing beneath mussel farming longlines deriving tissue carbon from sediment impacted by farming activities. This hypothesis is further supported by the finding that the isotope signature of sediment collected from beneath the mussel farm is consistent with the expectation that sea cucumbers were feeding on and consuming sediment enriched with bivalve waste (faeces and pseudo-faeces). In contrast, the nitrogen stable isotope signature (δ15N) was found to be similar between sites for both sea cucumbers and assumed food sources. Both findings lend support to the viability of future sea cucumber/green-lipped mussel farm polyculture systems. Sea cucumbers in different locations (mussel farm, natural reef) possessed distinctly different isotope signatures, suggesting that mixing of sea ranched sea cucumbers with natural reef populations would be negligible or non-existent. Similarities between the isotope signatures in low metabolic tissue of sea cucumbers residing at the mussel farm site to that of mussel farm-impacted sediment suggest that cucumbers beneath mussel farms appear to have high rates of retention at the farm site. © 2010 The Authors. Aquaculture Research © 2010 Blackwell Publishing Ltd

Behavioural and anatomical measures of visual acuity in first-feeding Yellowtail Kingfish (Seriola lalandi) larvae

Ontogenetic change in the visual acuity of Seriola lalandi larvae was measured using both behavioural and anatomical techniques. Visual acuity improved over early development (day 4 to day 7 post-hatch), although for all three larval ages examined estimates of anatomical acuity were consistently lower (higher acuity) than estimates of behavioural acuity. At hatching the eyes of larval kingfish were characterized by an undifferentiated retina surrounding a spherical lens, by day 4 post-hatch the eyes appeared to be functional, the retina was fully pigmented and the optic nerve had made contact with the optic tectum. Analysis of prey search behaviour indicated that larvae employ a saltatory type search behaviour in which brief stationary periods are interspersed with repositioning movements. The mean reactive angle increased between day 4 and day 7 post-hatch indicating that the horizontal visual field was expanding with development, thereby increasing the search area of larvae. Pre-strike distances of early larvae were substantially less than one body length, being constantly around a 1/3 of a body length for all larval ages examined. © 2010 Springer Science+Business Media B.V

Effects of dietary enrichment with alpha-tocopherol acetate and post-harvest filleting on lipid oxidation and flesh quality of tropical farmed barramundi (Lates calcarifer)

Pre-harvest dietary enrichment with α-tocopherol acetate in combination with different post-harvest processing techniques was investigated with regard to quality degradation of farmed barramundi (Lates calcarifer), during chilled storage. Fish were fed commercial rearing diets supplemented with two levels of α-tocopherol acetate (standard level 192 mg kg-1 and enriched level 628 mg kg-1). During 5months of feeding, α-tocopherol content of fish fed the enriched diet increased significantly from an initial concentration of 13.67 to 24.18 mg kg-1 after 56days. After this period fish were harvested and subjected to 14day chilled (2°C) storage as either fillets or whole ungutted fish. Dietary α-tocopherol enrichment in combination with storing fish whole and ungutted constrained lipid oxidation over 14days of storage, in comparison lipid oxidation was significantly higher in fish fed the standard diet and filleted prior to storage. Filleting also resulted in significant colour changes with reddening and yellowing of the flesh in conjunction with significantly lower flesh pH compared to barramundi stored whole and ungutted. These results indicate that dietary enrichment with α-tocopherol acetate in combination with storing fish whole and ungutted is the most effective strategy in constraining lipid oxidation and colour fluctuations in barramundi flesh during chilled storage. Statement of relevance: Our findings show that dietary enrichment with α-tocopherol acetate, combined with whole ungutted storage, is effective in preventing lipid oxidation and associated deteriorations in product quality in farmed barramundi flesh during chilled storage. These findings can be used to optimise shelf life of tropical farmed fish. © 2015 Elsevier B.V

Highly localised distribution patterns of juvenile sea cucumber Australostichopus mollis

Information on the environmental characteristics of the juvenile habitat of many deposit-feeding sea cucumber species is limited, despite most fished species exhibiting rapid localised depletion. The current study combined large and small scale surveying techniques within a New Zealand harbour to identify areas with high densities of juvenile Australostichopus mollis, a commercially valuable aspidochirote holothurian. Data from detailed surveys were used to relate densities of juveniles and adults with measures of physical habitat characteristics including depth, sediment facies type, grain size range, as well as measures of chlorophyll-a, phaeopigment, carbon and nitrogen content of surface sediment. Results revealed a highly localised distribution of juvenile A. mollis focused on one site associated with an area of high adult density. Sites of high juvenile A. mollis density were characterised by sediment qualities favouring epibenthic detritivorous deposit feeding, including high nitrogen content, high phaeopigment:chlorophyll-a ratio and small grain size. The high-density juvenile site had facies that were further characterised by the presence of large shell fragments (>10 cm length) of the horse mussel (Atrina zelandica), which may provide a unique settlement microhabitat for early juveniles. Unlike some other sea cucumber species, juvenile A. mollis shows no distinct spatial separation from adult sea cucumbers, no association with dense macroalgae and no clear preference for shallower depths than adults. Overall, the results illustrate the highly localised pattern of recruitment of this species to a widely distributed adult population, which may help to explain the lack of previous observations of juveniles in this species. These results indicate the importance of identifying and protecting what appear to be very specific juvenile habitats in deposit-feeding sea cucumbers to ensure continuing recruitment to exploited populations

Open-top static respirometry is a reliable method to determine the routine metabolic rate of barramundi, Lates calcarifer

Closed-system respirometry is a standard technique used to determine aerobic metabolism of aquatic organisms. Open-top systems are rarely used due to concerns of gas exchange across the air-water interface. Here, we evaluated an open-top respirometry system by comparing the mass-specific routine metabolic rate (RMR) of the tropical diadromous finfish barramundi, Lates calcarifer, in both closed-top and open-top respirometers. The RMR of 190 g barramundi was determined across broad temperatures ranging from 18 to 38 °C. There was no significant difference in RMR between barramundi in either closed- or open-top respirometers at any temperature (p > 0.05). To ensure RMR measurements were not an artifact of the respirometry system, barramundi were reciprocally transplanted into either respective closed-top or open-top respirometer and oxygen consumption re-measured at each temperature treatment. The RMR of transplanted barramundi was found to be virtually identical in either respirometer. RMR increased linearly with increasing temperature; the relationship between RMR and temperature (T; 18-38 °C) can be described as 3.658T-36.294 mg O2 kg-0.8 h-1. The daily energetic cost of RMR was 1.193T-11.838 kJ kg-0.8 day-1. Q10 for barramundi increased significantly with increasing temperature (p < 0.0001). Q10(18-28) was the lowest at 1.7 and Q10(28-38) the highest at 1.9, over the whole experiment temp range Q10(18-28) was 1.8. The current study demonstrates that open-top respirometry is a reliable and practical alternative to closed-top respirometry for accurate determination of the aerobic metabolism of barramundi and has potential application for a number of different aquatic organisms. © 2014 © 2014 Taylor & Francis

Earthy-muddy tainting of cultured barramundi linked to geosmin in tropical northern Australia

Tainting of outdoor pond-reared barramundi Lates calcarifer by muddy-earthy offflavours is frequently reported across tropical Australia. To investigate the possible causes and effects of off-flavour tainting, we analysed water samples from outdoor rearing ponds for the presence of geosmin (GSM) and 2-methylisoborneol (2-MIB), 2 microbial metabolites often associated with tainting episodes. We then conducted controlled doseeffect experiments which measured the accumulation of tainting metabolites in the flesh, and the impact tainting had on taste and flavour attributes. GSM was deemed to be the compound most likely responsible for off-flavour tainting, persisting at moderate (~1.00 μg l-1) to extreme levels (~14.36 μg l-1), while 2-MIB was never detected during the study. Controlled experiments revealed that the accumulation of GSM in the flesh of market-sized barramundi was directly related to GSM levels of the holding water (0 to ~4 μg l-1), with higher levels resulting in significant increases in undesirable taste and flavour attributes, particularly muddy-earthy flavour and weedy aftertaste. We identified the sensory detection threshold for GSM in farmed barramundi to be ≤0.74 μg kg-1, similar to estimates for GSM detection in rainbow trout Oncorhynchus mykiss (~0.9 μg kg-1) and for 2-MIB in channel catfish Ictalurus punctatus (0.7 μg kg-1). Quantitative estimation of flesh-bound GSM using gas chromatography-mass spectrometry (GC-MS) agreed well with human sensory assessment scores and highlights the reliability of chemical analysis of GSM in barramundi flesh while also indicating the value of GC-MS analysis in predicting the impact of GSM on the sensory properties of farmed barramundi. © Inter-Research 2013

Flavour enhancement of freshwater farmed barramundi (Lates calcarifer), through dietary enrichment with cultivated sea lettuce, Ulva ohnoi

Nutrition plays an important role in shaping the organoleptic properties of fish as key flavour compounds are principally sequestered from the diet. Conventional aquaculture feeds are primarily formulated to maximise somatic growth with little consideration given to the effect on organoleptic attributes such as flavour, taste and aroma. We assessed the efficacy of the marine macroalgae Ulva ohnoi to alter the organoleptic properties of cultured freshwater barramundi (Lates calcarifer) by feeding a short term finishing diet. Barramundi were finished on diets containing 0%, 10%, 20% and 30% of dried U. ohnoi for 7, 14 and 21 days. Following harvest the organoleptic properties of fish were subjected to human sensory assessment. The flavour of barramundi finished on diets containing ≥. 20% inclusion level of U. ohnoi was described as being more 'desirable', 'sweeter', and 'rich and complex' when compared to fish finished on a standard commercial rearing diet. Fish finished with U. ohnoi also developed a crab-like/seafood flavour and a cooked crab aroma, resulting in significant increases in these organoleptic attributes. Fillets were subsequently analysed for bromophenol compounds and dimethylsulfide. Bromophenols were not detected at any time in fillets of barramundi that were finished on either U. ohnoi or a standard commercial diet. However, dimethylsulfide was found to be more elevated (~. 8 fold) in fish fed U. ohnoi. Feeding cultured freshwater fish a diet containing the marine algae U. ohnoi was effective in altering the organoleptic profile of fillets, imparting a rich and complex seafood-like flavour. The potent flavour compound dimethylsulfide was associated with this change and appears to be a key flavour compound in this instance. The application of a finishing diet that enhances flavour and aroma properties pre-harvest would enable aquaculture growers to exert direct control over these properties. This is especially important for freshwater finfish species as growers could conceivably produce fish that have organoleptic similarity with wild caught marine species. Statement of relevance: A functional feed providing a mechanism to produce low cost freshwater fish with flavours that are more characteristic of wild caught marine species is presented. This diet caused farmed freshwater fish to develop marine aromas and flavours and increased sweetness and flavour complexity during 21 days of feeding. © 2015 Elsevier B.V

Physiological plasticity v. inter-population variability: Understanding drivers of hypoxia tolerance in a tropical estuarine fish

Physiological plasticity and inter-population variability (e.g. local adaptation) are two key drivers in determining the capacity for species to cope with environmental change, yet the relative contribution of each parameter has received little attention. Here, we investigate the acclimation potential of two geographically distinct populations of the barramundi (Lates calcarifer) to diel hypoxia. Fish were exposed to a daily hypoxia challenge of 6h below 62% saturation, down to a minimum of 10±5% saturation, followed by a return to normoxia. Respiratory and haematological variables were assessed after 8 and 16 days of daily hypoxia exposure. Hypoxia tolerance (measured as the critical oxygen tension; [O2]crit) was not different between populations and not different from control fish after 8 days ([O2]crit≤20.7±2.8% saturation), but improved similarly in both populations after 16 days ([O2]crit≤16.5±3.1% saturation). This improvement corresponded with increases in haematocrit and haemoglobin, but not an increase in the mean cell haemoglobin concentration. Given the similarity of the response between these two geographically distinct populations, we conclude that hypoxia tolerance for barramundi may be more dependent on physiological plasticity than inherent variability between populations. © CSIRO 2016