Introduction
Jade Perch, Scortum barcoo, is an excellent species for recirculating aquaculture systems (RAS). It is a freshwater finfish native to Australia and an upcoming aquaculture species in South East Asia, China, Australia and Europe. Because this is a fast growing, low trophic omnivore species that can be grown on a 100% plant based diet, without negative effects on growth or filet quality, it has great potential to contribute to the development of sustainable aquaculture in Europe (Van Hoestenberghe et al., 2016; Liu et al., 2014).
Controlled reproduction of new species that are suitable for RAS systems is a prerequisite to combine intensive aquaculture with environmental sustainability of the industry (Martins et al., 2010). For the development of controlled reproduction a species-specific broodstock diet plays an important role, together with other environmental factors such as photoperiod and temperature (Izquierdo et al., 2001; Wang et al., 2010). As for many other species new to aquaculture, an unpredictable and variable reproductive performance is an important limiting factor for the mass production of juveniles and the success of the species. By improving broodstock nutrition it has been shown that egg quality, sperm quality and seed production can greatly be improved. From all the essential dietary nutrients that play an important role in reproduction, lipids and fatty acids have been determined as major dietary factors for a successful reproduction and survival of offspring (Izquierdo et al., 2001). The n-3 highly unsaturated fatty acids (HUFAs) DHA and EPA, as well as the n-6 HUFA ARA play and important role in the reproductive cycle of fish (Henrotte et al., 2010). DHA plays a crucial role in the development of neural and visual functions during the early ontogeny of fish. ARA is the main precursor of the 2-series prostaglandins, a type of eicosanoid (Rainuzzo et al., 1997). EPA is also a precursor of eicosanoids that are involved in several reproductive processes, the 3-series prostaglandins. EPA and ARA compete for the same enzymes (cyclooxygenase and lipoxygenase) to be converted into prostaglandins. This is one of the reasons why the ratios of the different fatty acids also play an important role in reproduction (Henrotte et al., 2010; Izquierdo et al., 2001).
Although some aspects of its larval rearing and cryopreservation of spermatozoa have been described, until today no published research has appeared on the reproduction of Jade perch in RAS. The aim of this research is to evaluate the effect of different broodstock diets with specific fatty acid compositions on Jade Perch reproduction.
Materials and methods
The broodstock used for this trial is a F1 generation from Australian wild Jade perch broodstock and was 5 years old at the start of the trial. They were held under a natural (Australian) photothermal regime in recirculating systems. A whole reproductive cycle was simulated over 12 months starting with autumn and ending with summer. The 108 individuals (72 males and 36 females) were randomly stocked in twelve 1800-l tanks.
Three different slow sinking feeds, each containing approximately 6% fat, 40% proteins and 7% carbohydrates, but with a different fatty acid composition were formulated. Feed 1 has a DHA/ARA/EPA ratio of 1/0.1/0.0, Feed 2 has a DHA/ARA/EPA ratio of 1/0.1/0.4 and Feed 3 has a DHA/ARA/EPA ratio of 1/0,8/0,1. Four treatments were studied in triplicate. Treatment 1 received feed 1, treatment 2 received feed 2, treatment 3 received feed 3 and treatment 4 received feed 3 supplemented with live black soldier fly larvae.
During the reproductive season different parameters were measured: maturation stage of oocytes, percentage of ovulated eggs, percentage of oil droplet fragmentation, the total number of collected eggs, the average egg mass, amount of milt collected, sperm motility, duration of sperm activity, larval oil droplet size, percentage of hydrated eggs and percentage of fertilised eggs.
Results
At the time of submission, the trial was still ongoing. As a consequence the results could not be enclosed in this abstract, but will be given at the presentation.
Discussion and conclusion
Literature suggests that DHA is essential in broodstock diets and has a positive effect on reproduction. ARA and EPA compete for the same enzyme to be converted to prostaglandins. It is suggested that a high ARA/EPA ratio has a positive effect on reproduction (Henrotte et al., 2010). In an attempt to have a diet that more closely resembles the natural diet of Jade Perch, live black soldier fly larvae were added to the diet in treatment 4 (Balcombe et al., 2005). This could possible further increase the reproductive performance of our Jade Perch broodstock held in RAS systems.
References
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