Marking Effect of Coded Wire Tag on Released Juveniles of Black Rockfish (Sebastes schlegelii)

Abstract

Black rockfish (Sebastes schlegelii) is a member of the family Sebastidae—an ovoviviparous marine fish widely distributed in the coastal waters of China. This species has important commercial value and is also a delicious table fish. It often inhabits areas at the bottom of the sediment in rocky reefs with clear water quality. The species does not exhibit a long-distance migration habit or remarkable clustering. In recent years, sea ranching has developed rapidly in China. Black rockfish is a good candidate to promote sea ranching, because it does not exhibit a long migratory habit and is called a housekeeping fish. In recent decades, owing to the overfishing of wild resources and deterioration of the environment, the natural pools of black rockfish have decreased sharply. Thus, the national black rockfish release and breeding plan was implemented in 2006. Currently, millions of young black rockfish are released into the sea every year in China, which has played a positive role in promoting the conservation and restoration of natural resources. However, the release activity of marine organisms is random and under lax supervision. In recent years, various tagging technologies, including external markers, such as T-bar markers, and internal markers, such as otolith markers, have been developed to support the evaluation of the enhancement effect of released species. At present, otolith fluorescent labeling is the only reported marker technology that can be used for the proliferation and release of black rockfish. However, otolith staining has some problems, such as difficulty in detection and rapid fading, and it is not effective as an internal marker. Currently, there has been no efficient internal marker for black rockfish juveniles; thus, an effective marking technology must be established for evaluating the enhancement effect of black rockfish to support scientific release and natural resource maintenance. The coded wire tag (CWT) is a magnetized stainless-steel wire segment with a diameter of 0.25 mm. Several rows of numbers are engraved on the marking line to represent a specified batch or a single code. CWTs are widely used internal tags with many advantages, including small size, easy management, accuracy, and high retention. CWTs have been effectively used in over 30 fish genera worldwide because of their high retention rates and minimal biological impact on living fish, although serious effects on growth and survival have been reported among different species and tag placements. In the present study, we investigated the marking effects of CWTs on released juveniles of black rockfish. According to different sizes and marking placements, the experimental juveniles of black rockfish were divided into four groups: small fish [average total length = (8.25±0.84) cm, average body weight = (9.99±2.75) g ] with gill levator arcus palatine muscle tagging group (SLM group); small fish with dorsal muscle tagging group (SDM group), large fish [average total length = (11.13±0.67) cm, average body weight = (20.95±2.99) g ] with gill levator arcus palatine muscle tagging group (SDM group); and large fish with dorsal muscle tagging group (LDM group). The survival rate, tag retention, antioxidant enzyme activity, and expression of genes related to growth or stress were measured to evaluate the effects of CWTs on black rockfish juveniles. The survival rate was 100% in all study groups. The tag retention rates in the SLM and LLM groups were 87% and 97%, respectively. The tag retention rate in the SDM and LDM was 100%. The specific growth rate of all tagged fish was lower than that of the control fish. After 30 days of culture post-tagging, the liver catalase enzyme activity in the SLM and LDM groups was significantly higher than that in the control group, and the liver superoxide dismutase enzyme activity in all experimental groups was significantly higher than that in the control group. The liver IGF-I mRNA levels were significantly higher in the SLM, LLM, and LDM groups than in the control group. There were no significant differences in HSP70 mRNA levels between the small fish groups, while in the large fish groups, HSP70 mRNA level in the LDM group was lower than that in the LLM and control groups. Therefore, CWT is suitable for marking black rockfish juveniles based on survival and tag retention data; however, the specific growth rate of tagged fish was lower than that of the control fish, and the antioxidant enzyme activities and expression of genes related to growth and stress showed significantly different expression responses to CWT marking, indicating that tagging caused physiological stress in released black rockfish juveniles. Therefore, indoor temporary breeding or wild domestication time should be relatively long for the seedlings marked with CWTs, which is conducive to improving the survival rate of the marked released seedlings and their growth after release. Overall, CWTs may be useful to evaluate the enhancement effects of released species and support accurate assessments of the proliferation and release effect of black rockfish.

Keywords

• sebastes schlegelii
• juvenile
• coded wire tags
• tagging effects
• physiological response