TOWARDS SUSTAINABLE AQUACULTURE: OMEGA PERCH IN RECIRCULATION SYSTEMS

With juvenile Omega Perch Therapon barcoo, the substitution of dietary fish oil with plant oils in diets with 20% fishmeal didn’t result in a growth deficiency or a difference in fillet recovery. However, when fishmeal free diets were used, there was a certain growth reduction, indicating that juvenile Omega Perch require a minimum amount of about 0.5% of n-3 HUFA in their diet. These dietary n-3 HUFA can be supplied with Schizochytrium; low dietary amounts of these protists don’t cause an inferior fillet quality. DHA from Schizochytrium is stored more efficiently in the fish compared to DHA from fish oil, and the fillet recovery increased when fish were fed Schizochytrium. Both fat and the fatty acid spectrum of the fish fillet are directly proportional to the respective content of the feed. Omega Perch can have up to 3.75% n-3 PUFA in their fillet, one of the highest values ever recorded in fish. A whole body fatty acid survey and qRT-PCR demonstrate that Omega Perch can desaturate and elongate n-3 PUFA towards long chained n-3 HUFA. After hatching from the egg, Omega Perch start exogenous feeding at 3 DPH (Days Post Hatching) and are only 0.3 mg in size. In RAS, the optimal weaning age when Artemia are supplied is at 12 DPH with a further 3 days of co-feeding with dry micro diets before a switch to 100% dry feed can occur. Feeding the larvae the first 3 days of exogenous feeding with smaller sized AF Artemia before switching to EG Artemia resulted in a lower survival (>1%) compared to feeding only EG Artemia (9% survival). This indicates that smaller sized live prey would not result in better survival. When larvae are weaned at 13 DPH, they weigh around 12 mg and reach 140 mg (fingerling size) after 3 weeks of exogenous feed consumption. When the correct feeding strategy is applied, an average survival and fast growth is obtained, to ensure adequate fingerling production. In RAS without denitrifying reactors, nitrate levels determine the water exchange rate. Denitrification occurs in anaerobic heterotrophic reactors with an adequate C/N ratio. In a RAS with Omega Perch fed a 40% protein diet, a sequence batch reactor (SBR) with an alternating anaerobic and aerobic phase can reduce the water exchange from 550 to 30 l per kg of feed. Furthermore, the solids waste stream of the drum filter can be used for adequate denitrification. Dephosphatation occurs, but is rather small compared to denitrification. The SBR has a small but negative impact on other water parameters (CO2, NH3 and NO2) which should be taken into account when dimensioning the components of the RAS system. Off flavour producing bacteria occur in the SBR, however it is unclear if the SBR is responsible for a net increase in off flavour, since adsorption of off flavour in the sludge of the SBR might occur. In short, we report some criteria for sustainable aquaculture of a new species for the European consumer: Omega Perch . Without the use of dietary fishmeal and fish oil, and a low water usage, Omega Perch grows well in recirculation systems. An adequate dietary n-3 source enables a high concentration of n-3 in its flesh.status: publishe

Total replacement of fish oil with vegetable oils in the diet of juvenile jade perch scortum barcoo reared in recirculating aquaculture systems

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Automatic underwater weight estimation of omega perch by computer vision

The aim of this study was to test and evaluate a computer vision technique that estimates the weight of Omega Perch swimming freely in a tank of a recirculation aquaculture system. A set of 105 images of fish were captured out of the water in order to build up a relationship between the fish shape and its weight. Regression analysis revealed that the coefficient of determination (R2) between area and weight is 0.98. Based on this model the mean predicted error weight is 9±7% when compared with the value measured by a weighing scale. This model was then used to estimate the biomass of 15 fish that were moving freely through an underwater corridor where a camera was installed. The results revealed a 10±5% estimation error when compared with the value measured by a weighing scale. Therefore the proposed method might be useful for continuously and automatically estimating the biomass of freely swimming fish without causing stress or damage to them.status: publishe

Effect of weaning age and the use of different sized Artemia nauplii as first feed for jade perch Scortum barcoo

The first days of exogenous feeding are crucial for larval recruitment. A correct first prey item and the determination of the optimal weaning age, can reduce labor cost and fish mortality to a great extent. This study was conducted to evaluate the use of small and regular Artemia fransiscana (AF and EG Artemia, Inve, Belgium) as first feed for jade perch Scortum barcoo, and to determine the minimum required duration of this life feed phase before transition to dry feed can occur. Therefore, we compared first feeding of 3 days AF nauplii instar I with 3 days of EG nauplii instar I and evaluated whether the optimal weaning age for jade perch larvae was at 7, 10, 13 or 16 days post-hatching (DPH). The study was performed in 25-L tanks in a recirculating system and lasted for 21 days (4-24 DPH). Growth, survival and tissue fatty acid composition of the larvae in the different treatments were analyzed. Results indicate that, after the start of exogenous feeding at 4 days DPH, jade perch larvae require a minimum of 9 days of live feed until 12 DPH. Co-feeding ideally starts on 10 DPH. Larvae fed AF Artemia for the first 3 days showed a significantly faster growth than larvae fed EG Artemia, although their survival was lower. Gape width of larvae at 3 and 6 DPH was measured, and implications for prey size are discussed

Effect of weaning age and the use of different sized Artemia nauplii as first feed for jade perch Scortum barcoo

The first days of exogenous feeding are crucial for larval recruitment. A correct first prey item and the determination of the optimal weaning age, can reduce labor cost and fish mortality to a great extent. This study was conducted to evaluate the use of small and regular Artemia fransiscana (AF and EG Artemia, Inve, Belgium) as first feed for jade perch Scortum barcoo, and to determine the minimum required duration of this life feed phase before transition to dry feed can occur. Therefore, we compared first feeding of 3 days AF nauplii instar I with 3 days of EG nauplii instar I and evaluated whether the optimal weaning age for jade perch larvae was at 7, 10, 13 or 16 days post-hatching (DPH). The study was performed in 25-L tanks in a recirculating system and lasted for 21 days (4–24 DPH). Growth, survival and tissue fatty acid composition of the larvae in the different treatments were analyzed. Results indicate that, after the start of exogenous feeding at 4 days DPH, jade perch larvae require a minimum of 9 days of live feed until 12 DPH. Co-feeding ideally starts on 10 DPH. Larvae fed AF Artemia for the first 3 days showed a significantly faster growth than larvae fed EG Artemia, although their survival was lower. Gape width of larvae at 3 and 6 DPH was measured, and implications for prey size are discussed.status: publishe

Incorporation of black soldier fly larvae (hermetia illucens) in the diet of omega perch (therapon barcoo)

Due to the high need and inclusion of fish oil and fish meal in diets of most cultivated fish in our Western world, much more kilogram of fish are used to produce these fish than they produce (Van Hoestenberghe et al. 2013). For many fish species in the wild, insects are a substantial part of their natural diet. Insects can be a new alternative for fish meal in aquaculture diets. Black Soldier Fly (Hermetia illucens) pre-pupae meal might be a suitable alternative for fish meal due to the amount of protein, fat and well balanced essential amino acid profile (Kroeckel et al 2012). The use of Black Soldier Fly in aquaculture nutrition could contribute significantly to the sustainability of fish farming by lowering pressure on natural fish stocks, as well as by converting organic side streams (from agriculture, fruit and vegetable processing facilities, retail,..) to nutritionally valuable feed ingredients. The Omega Perch (Therapon barcoo) is an aquaculture species new for Europe that performs well in recirculating aquaculture systems (RAS) and feeds on grow-out diets with very low or no dietary levels of fishmeal and fish oil. The present study was undertaken to compare production parameters of Omega Perch fed on diets with different mix ratio between Black Soldier Fly larvae and extruded feed pellets.status: publishe

Schizochytrium as a replacement for fish oil in a fishmeal free diet for jade perch, Scortum barcoo (McCulloch & Waite)

© 2016 John Wiley & Sons Ltd. A 10-week trial was conducted to determine the response of juvenile jade perch Scortum barcoo on the replacement of dietary fish oil (FO) in a fishmeal free diet. Three iso-nitrogenous, isocaloric and isolipidic diets were formulated, each containing a different primary fat source: FO, linseed oil (LO), and a mixture of Schizochytrium and LO. The substitution of FO with the mixture of Schizochytrium and LO did not cause a difference in growth. However, there was an 8% reduction in weight gain in fish fed dietary LO, indicating that juvenile jade perch do require a minimal concentration of dietary n-3 highly unsaturated fatty acids (HUFA). Fish fed the Schizochytrium diet stored more efficient n-3 HUFA and in particular DHA in their flesh, and retained a higher fillet recovery compared to fish fed FO. In addition, we demonstrated that jade perch are able to produce both n-3 HUFA and n-6 HUFA when dietary PUFA are present. Fish fed the LO diet for 10 weeks contained the lowest amount of n-3 HUFA in fillets among dietary treatment groups. However, feeding these fish the Schizochytrium diet for an additional 4 weeks increased the n-3 HUFA content towards the same concentration of n-3 HUFA found in the flesh of fish fed FO, without affecting the sensory properties of the fillets. In contrary, feeding the Schizochytrium diet for a continuous period of 14 weeks lowered overall sensory property scores.status: publishe