Optimal Salinity for Head-Starting Northern River Terrapins (Batagur baska Gray, 1831)

Abstract

Simple SummaryNorthern river terrapins can adapt physiologically or behaviorally across a salinity gradient, so that they can move between freshwater habitats and brackish water or estuaries. However, there is no available information on the optimal salinity of this species for supporting captive husbandry programs before release to natural habitat. In the current study, the optimal salinity for the terrapins was investigated to serve the well-being of turtles. At the end of the rearing period, various observed parameters related to growth, feed utilization, and health indicated that optimal salinity for rearing the terrapins is about 4 ppt, while rearing in freshwater (0 ppt) or other brackish (8 and 12 ppt) water conditions had negative effects on some key parameters that reflect well-being. A polynomial regression fit to terrapin weight gain as function of salinity predicts the optimal salinity as 4.35 ppt. Findings from the current study could be directly used in ex situ conservation programs of northern river terrapins before release to natural habitat. Additionally, concurrent conservation and restoration of the wild habitats with preferred salinity is essential for flourishing terrapin population.AbstractNorthern river terrapins (Batagur baska Gray, 1831) are Asia’s largest turtles living in both freshwater and brackish water. In the current study, the optimal salinity for head-starting programs of this critically endangered species was investigated in order to serve the well-being of turtles before release to natural habitat. Forty-eight terrapins (54.64 ± 0.18 g initial body weight) were randomly distributed to four salinity levels (0, 4, 8, and 12 ppt) and reared for eight weeks, using three replicates with four terrapins each. At the end of rearing trial, growth performance and feed utilization parameters were superior in terrapins reared at 4 ppt, followed by 8 ppt in the rank order of treatments. Negative stress responses were observed in terrapins reared at 12 ppt, as the fecal activity of amylase-to-trypsin ratio was changed significantly, but not that of proteolytic enzymes. The fecal thermal transition properties indicated an abundance of nutrients in the post-absorptive phase for terrapins reared at 4 ppt, followed by the 8 ppt treatment group. The preferred 4 ppt salinity had no negative effects on the health status of the terrapins in terms of carapace elemental composition or hematological parameters. Second-order polynomial regression suggests 4.35 ppt as the optimal salinity for maximal weight gain. Findings from the current study could be directly used in ex situ conservation programs of northern river terrapins before release to natural habitat.

Optimal Feeding Frequency for Captive Hawksbill Sea Turtle (Eretmochelys imbricata)

“…Hawksbill sea turtles fed by 2M8–16 had a better performance, followed by 2M12–16 or 3M8–12–16. The optimal frequency found from the current study matches with the routine feeding schedule of hawksbill sea turtles in Thailand, as well as with the reported head-starting programs of the same species [ 32 ] and northern river terrapins, Batagur baska [ 17 ]. Moreover, two meals daily (07.00 and 16.30 h) is appropriate for green turtles when compared with one (13.30 h), three (07.00, 11.30, and 16.30 h) and four meals daily (07.00, 10.30, 13.30, and 16.30 h) [ 9 ], or for soft-shelled turtles when comparing two meals daily (10.00 and 17.00 h) with one meal daily (17.00 h) [ 10 ].…”

“…No differences in BCI indicate normal morphometric changes of reared turtles over the range of feeding frequencies tested. Generally, elemental composition in carapace reflects the varying feeding regimens or the physical conditions where the animals lived [ 9 , 17 , 18 , 40 ], whereas hematological parameters are influenced by seasonal changes, age, sex, geographical location, physiological responses, and reproductive status [ 50 ]. No differences in carapace elemental composition and hematological parameters between the turtles fed 2M8–16 and the other remaining treatments suggest no negative effects on health status by the treatments.…”

“…In addition, as a non-invasive technique, the thermal property study can also be used to detect unavailable and available nutrients in feces after digestion and absorption. This technique can be applied in the feeding trials of various aquatic animal models [ 9 , 17 , 18 , 19 ].…”

“…The well-being of turtles in a captivity program can be assessed from the carapace elemental composition and hematological determinations [ 9 , 17 , 18 ]. This is because the feeding regimens directly influence the metabolites present in blood and the accumulation of nutrients in the carapace.…”

Optimal feeding frequency for bigfin reef squid (Sepioteuthis lessoniana)

“…The thermal transition properties of bigfin reef squid faeces ( n = 9 per treatment) were determined as described in Jualaong et al (2019). The flesh faeces were pooled and dried using a freeze dryer (Delta 2‐24 LSC, Martin Christ Gefriertrocknungsanlagen GmbH) for 24 h to eliminate the interference by water.…”