Pre‐soaking of the feed pellets: a trick for successful feed utilization in juvenile green turtles (Chelonia mydas Linnaeus, 1758)

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Green turtle (Chelonia mydas Linnaeus, 1758) is listed as a marine endangered species, and is protected against over exploitation by the International Union for Conservation of Nature (IUCN) and the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). This species is carefully propagated in Thailand within 1 year after hatching, prior to release in natural habitats, under the Department of Marine and Coastal Resources, Ministry of Natural Resources and Environment. This ex situ conservation program has attempted to increase the survival and fitness of juvenile turtles before they encounter real ecosystems. Over three decades, various artificial feeds for marine species have been selected and accepted for use in green turtles (Wood and Wood, 1981; Jones et al., 2009; Price et al., 2013; Kanghae et al., 2014a,b). However, the survival and the growth quality of juvenile green turtles are still poor in such rearing, partly due to undeveloped husbandry protocols, especially in the feeding techniques.
Recently, a preparation trick by pre‐soaking the feed pellets in water, prior to use in feeding, has contributed to the successful rearing of juvenile green turtles (Kanghae et al., 2014b). On the other hand, feeding unsoaked pellets was inferior in survival, growth and feed utilization of green turtles, relative to feeding fish fillet (Ruangkaew and Buakaew, 2005). Moreover, sea turtles fed with commercially prepared pellets can develop floating‐bloating problems when overfed (Fontaine et al., 1985), and even when not overfed (Higgins, 2003). Pre‐soaking the feed in water might have reduced the abdominal bloating of turtles, a condition that may lower the survival of juveniles. For terrestrial animals, increases in phosphorous availability and retention were obtained with pre‐soaked feed (Näsi et al., 1995; Esmaeilipour et al., 2013). Such findings correlate well with the improvements in chemical composition, physicochemical properties and digestibility of some feed ingredients, observed from pre‐soaking in water (Wina et al., 2005; Chumwaengwapee et al., 2013; Thongprajukaew et al., 2013b). These findings suggest that feed utilization is affected by pre‐soaking. Such positive effects might be pursued further by optimizing the pre‐soaking parameters, in particular the mixing ratio of water and feed pellets.
The aim of this study was to optimize the soaking ratio of pellet feed, specifically for the rearing of juvenile green turtles. The soaking ratio 0.3 (1:0.3 w/v of pellet to water) used in an earlier study (Kanghae et al., 2014a) was used as the baseline control and compared to the higher soaking ratios 0.5 and 0.7. Non‐pre‐soaking treatment was not performed as it is already known to cause high mortality in this species (Ruangkaew and Buakaew, 2005). Protection by IUCN, CITES and Wildlife Preservation and Protection Act in Thailand support this as the proper choice. The success in production of head‐started turtles was evaluated based on observation techniques that were unobtrusive, non‐invasive and without ethical concerns. The digestive function was assessed from faecal carbohydrate‐digesting enzymes (amylase and cellulase), lipid‐digesting enzyme (lipase) and protein‐digesting enzymes (pepsin, trypsin and chymotrypsin). These enzymes have been used in assessing green turtles for their digestive physiological acclimation, which relates to feed utilization (Kanghae et al., 2014b; Thongprajukaew et al., 2014). Moreover, faecal digestive enzymes have become an important tool for biochemical, physiological and ecological studies (CÓrdova‐Murueta et al., 2003, 2004). The direct assessment of faeces has been used for nutritional evaluations in fish (Amirkolaie et al., 2006), in birds (Varo and Amat, 2008), as well as in green turtles (Amorocho and Reina, 2008; Kanghae et al., 2014a,b). Moreover, changes in the thermal transition properties can be used for evaluating available nutrients present in faeces (Thongprajukaew et al., 2014).
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