Broodstock condition, egg morphology and lipid content and composition during the spawning season of captive striped trumpeter, Latris lineata

Abstract

The striped trumpeter, Latris lineata, is a pelagic marine fish found in southern Australia that is currently being developed as an aquaculture species. Striped trumpeters are multiple spawners with group synchronous oocyte development and spawn in the wild from late winter to early spring. By shifting light and temperature regimes, it is possible to manipulate broodstock to spawn in captivity outside of their normal ambient season. Broodstock condition, egg morphology and biochemistry were examined over a spawning season for three groups of broodstock held under ambient or photothermal-manipulated (PTM) conditions. Using a Torry Fish Fatmeter the muscle fat of male and female striped trumpeter broodstock held under ambient conditions was found to decrease over a season by 25% and 40%, respectively. Five general trends were observed in eggs spawned during both ambient and PTM seasons. First, overall egg volume remained unchanged. Second, the egg oil droplet volumes decreased to < 80% of those measured at the start of the spawning season. Third, there was a decrease in the triacylglycerol (TAG) fraction of egg total lipid and a concomitant increase in the proportion of polar lipid (PL). Fourth, the relative proportions of egg monounsaturated fatty acids (MUFA) decreased over a breeding season, probably as they were depleted because of the energy requirements of vitellogenesis. Fifth, proportions of the essential fatty acids (EFA), 20:4n-6 (arachidonic acid, ARA), 20:5n-3 (eicosapentaenoic acid, EPA) and 22:6n-3 (docosahexaenoic acid, DHA) was typical of marine fish eggs (1.8%, 10.1% and 20.9% of total fatty acids, respectively), and remained unchanged or were elevated in eggs over a season. Data suggest that holding broodstock under PTM or ambient conditions results in similar temporal changes in egg biochemistry, albeit more truncated during the PTM season. Despite ongoing feeding by striped trumpeter during spawning, the total energetic cost of vitellogenesis results in a depletion of lipid in the muscle that is in turn reflected in egg biochemistry. Finally fatty acid requirements for striped trumpeter larvae determined during the live feeding period are not too dissimilar from average egg fatty acid profiles, supporting the theory that egg values can provide a basis for estimating dietary requirements.