Abstract
Due to the decreasing resources of both inshore and offshore fisheries, many organizations have released fry to enhance their stock in recent years. The discrimination between wild and hatchery-reared individuals must be performed to assess the efficiency of the release. Fresh groundwater is generally used by hatchers in southwesternTaiwanto decrease salinity and to promote the growth of larvae prior to feeding; thus, the elemental composition of the otolith may be different in stocks, and this difference may be used for identification. This study used Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) to analyze the trace elements in the nuclei of otoliths from black porgy Acanthopagrus schlegelii, including six hatchery reared specimens from the Tainan County, three recaptured marked and ten captured unmarked specimens from the Miaoli County in Northwestern coast of Taiwan. Among the six hatchery and three recaptured marked specimens, which ranged from 4.9 to23.4 cmin body length, the nucleus zone (relative to within5 cmin size growth) of the otoliths showed higher magnesium concentrations than that observed on both edges. The distribution was similar to an inverse “V” shape. The otoliths also showed lower manganese concentrations near the nucleus and had higher values near the edges, resulting in a distribution similar to a “U” shape. According to the appeared shape of Mg2+/Ca2+ and Mn2+/Ca2+ ratio in the central area of the nucleus zone, this study determined six specimens which were from hatchery reared and three specimens were from wild among ten unmarked specimens captured from the Northwestern coast of Taiwan. Under the conditions used in this study, the absorption of calcium into the otolith was active and required energy in the seawater and freshwater, while the incorporation of magnesium and manganese was passive and was primarily affected by diffusion.
Highlights
In recent years, the release of fry from hatcheries to the wild is a common method of enhancing Taiwan’s natural fishery resources [1]
Fresh groundwater is generally used by hatchers in southwestern Taiwan to decrease salinity and to promote the growth of larvae prior to feeding; the elemental composition of the otolith may be different in stocks, and this difference may be used for identification
Among the six hatchery and three recaptured marked specimens, which ranged from 4.9 to 23.4 cm in body length, the nucleus zone of the otoliths showed higher magnesium concentrations than that observed on both edges
Summary
The release of fry from hatcheries to the wild is a common method of enhancing Taiwan’s natural fishery resources [1]. Many methods have been used for the identification and discrimination of fish stock, including the mark-and-recapture method, physiological and behavioral characteristics, morphology, and biochemical and molecular biology techniques These methods are useful but exhibit some disadvantages. Previous studies in Taiwan have suggested that distinguishing reared stocks from wild stocks of black porgy by morphology and meristic characters is difficult. The chemical composition of otoliths between the nucleus zone and the edge zone was analyzed in hatchery-reared, recaptured marked and wild unmarked black porgy. This is the first time that this method has been applied in Taiwan, and it may be an important tool for the identification of stocks, stocking assessment and management of fisheries
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