Abstract
Globally, wild seahorse populations are threatened due to, habitat destruction and unsustainable human exploitation among others. Furthermore, aquaculture-based mass-scale rearing is still uncommon due to the low survival rates of seahorse juveniles and exceptionally high feed costs. Previous studies have demonstrated the importance of both highly unsaturated fatty acid (HUFA) supplies and a copepod-based rearing for seahorse survival and growth. As the latter is expensive, the question arises as to how high survival rates of seahorse juveniles can be assured under low- to moderate-cost feed regimes. In particular, it remains unknown whether the diet species or their dietary HUFA profiles determine the successful development of seahorse fry. Therefore, the aims of this study were to assess the dependence of growth and survival rates of Hippocampus reidi brood on the animal feed and to infer the impact of feed species vs. dietary HUFA profiles on juvenile growth. A nutrition experiment was conducted where juveniles were treated either with enriched Artemia nauplii (low-cost diet Art) or with a mixed diet of Artemia and copepods (moderate-cost diet Art/Cop). Larval survival and growth were analyzed using Cox proportional-hazard and mixed linear model analyses. We found that i) both diets enabled good survival, ii) diet Art/Cop resulted in superior weight and height growth, and iii) the differential effects of diets Art/Cop and Art cannot be explained by their different HUFA compositions alone. From an economical point of view, our findings of high survival rates and relatively high growth rates with the medium-cost treatment Art/Cop may open new possibilities for the large-scale rearing of seahorses. Even the application of a low-cost Art diet might be appropriate for seahorse aquacultures as both survival and growth rates are only marginally lower compared to the former diet.
Highlights
Wild seahorse populations are threatened due to alteration and destruction of habitats as well as unsustainable exploitation, such as excessive usage for traditional medicine, decoration, and ornamental purposes (Vincent, 1996; Wabnitz et al, 2003; Evanson et al, 2011; Vincent et al, 2011)
The main findings of this study are: (i) Both the diet based on enriched Artemia nauplii and living/frozen copepods, and the diet solely based on enriched Artemia nauplii, provide sufficient nutrients and fatty acids to enable good survival and growth of juvenile seahorses
Diet Art/Cop resulted in superior weight and height growth in comparison to diet Art. (ii) The difference in height growth between treatments increased over time with juveniles of treatment Art/Cop showing a significantly increased final height. (iii) Due to higher amounts of highly unsaturated fatty acid (HUFA) in diet Art, the superior juvenile survival and growth performance with diet Art/Cop cannot be explained by different HUFA compositions alone
Summary
Wild seahorse populations are threatened due to alteration and destruction of habitats as well as unsustainable exploitation, such as excessive usage for traditional medicine, decoration, and ornamental purposes (Vincent, 1996; Wabnitz et al, 2003; Evanson et al, 2011; Vincent et al, 2011). Mass-scale rearing is still rare and commercial aquaculture for traditional medicine purposes is non-existent (Koldewey and Martin-Smith, 2010) This is mainly due to two reasons; (i) the low survival rates of seahorse juveniles (e.g., Woods, 2003; Foster and Vincent, 2004; Olivotto et al, 2011), and (ii) exceptionally high feed costs (e.g., Lavens and Sorgeloos, 1996). Seahorses are characterized by a relatively inefficient digestion system due to an underdeveloped stomach (Tipton and Bell, 1988; Kumaravel et al, 2010) and a short digestive tract transit time (Koldewey, 2005; Murugan et al, 2009; Deobagkar et al, 2012) They possess no significant fat reserves and are forced to have a high daily food intake (Koldewey, 2005; Wittenrich, 2007). Chang and Southgate (2001) found a significant correlation between mean survival of Hippocampus spp. juveniles and dietary n3-HUFA, EPA, and DHA contents
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