Optimal feeding frequency of captive head‐started green turtles (Chelonia mydas)

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The green turtle (Chelonia mydas) is an endangered and threatened marine species, protected in most countries against overexploitation by the International Union for Conservation of Nature (IUCN) and the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Head‐started propagation before release to natural habitat is pursued to improve the survival of newly hatched turtles. Artificial diets have been accepted to use in the 1‐year propagation programme ongoing in Thailand (Kanghae et al., 2014a,b). At the Cayman Turtle Farm, green turtles are fed entirely with fish food pellets (WSPA, 2012). With overfeeding this causes floating–bloating problems (Fontaine et al., 1985) that may emerge also without overfeeding (Higgins, 2003). In addition, turtles fed ad libitum in captivity are also prone to obesity and the fatty degeneration of liver (Solomon and Lippett, 1991). Appropriate feeding protocols for this species remain poorly known and need comparative assessments.
An optimal feeding frequency should be implemented in the routine feeding schedules. This could increase growth by improving food intake, as the appetite returns after gastric evacuation (Riche et al., 2004). However, very little information is available on the feeding frequency of reptiles, especially for endangered wildlife species such as the green turtle. Prior studies on the feeding frequency of turtles found effects on protein intake, digestibility and excretion (Lei, 2006), and on specific dynamic action (Pan et al., 2005). These effects might be caused by the amount of food intake affecting the secretion of digestive enzymes as well as digestibility (Garber, 1983). Recently, faecal digestive enzymes have been assessed in nutritional investigations of green turtles (Kanghae et al., 2014b). A similar approach has been an important tool for biochemical, physiological and ecological studies in crustaceans (Córdova‐Murueta et al., 2004). Moreover, thermal faecal characteristics relate to the feed utilization (Thongprajukaew et al., 2014). The techniques in these prior studies may support assessment of response to feeding frequency, including effects on the digestive efficiency in turtles.
Feeding could be one of the biggest stressors of animals reared under farming conditions, as it is quite different from that in their natural habitat (López‐Olmeda et al., 2012). Besides its nutritional effects, feeding frequency directly affects the welfare and the immune responses of a reared animal (Garcia and Villarroel, 2009). Haematological parameters are generally used to assess the health statuses of green turtles (Flint et al., 2010; Price et al., 2013). These parameters are influenced by seasonal changes, age, sex, geographic location, physiological state and reproductive status (Zhang et al., 2011). Moreover, the carapace elemental composition reflects the growth quality, because growing a healthy hard turtle carapace poses its requirements on the nutrition (Du, 2013).
The aim of this study was to optimize the feeding frequency for the mariculture of juvenile green turtles. Non‐invasive techniques without ethical concerns were used to evaluate the nutritional responses to various feeding frequencies. The measured parameters were growth, feed utilization, faecal characteristics, haematological parameters and carapace elemental composition. Findings from this study could be implemented as a routine feeding schedule in the head‐started propagation programme for juvenile green turtles.
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