| Both black rockfish (Sebastes schlegelii) and Japanese flounder (Paralichthysolivaceus) are widely distributed along the coastal areas of China, the Koreanpeninsula, and Japan. In recent years, the commercial catches of black rockfish andJapanese flounder, which have been important model species for stock enhancement,have significantly decreased due to habitat degradation and overfishing. With anattempt to better understand the wild survival dynamic of released juvenile blackrockfish and Japanese flounder, to correctly estimate the effectiveness of the stockenhancement strategies, and to provide useful methods to improving artificialreproduction technique, fisheries management and recruiting natural stock,fluorescent marking methods for black rockfish were researched, and themorphological marking methods, mark-recapture programs and release strategies forJapanese flounder were also studies. This paper consisted with four sections, and themain results were listed as follows:1. Juvenile black rockfish Sebastes schlegelii (30–40mm total length) wereimmersed in a range of tetracycline hydrochloride (TC) solutions at concentrationsranging from300to500mg l-1, alizarin complexone (ALC) solutions atconcentrations ranging from200to400mg l-1, calcein (CAL) solutions atconcentrations ranging from50to250mg/l, and alizarin red S (ARS) solutions atconcentrations ranging from100to500mg/l in filtered sea water (salinity of30) for24h, respectively. After a60-day growth experiment, clearly visible marks in sagittae,asteriscus and fin spines under normal light (score≥4) were observed atconcentrations of200–400mg l-1,250–400mg l-1and250–400mg l-1ALC and200–500mg/l,300–500mg/l and200–500mg/l ARS, respectively. Scales and fin rays showed acceptable marks at much higher concentrations (≥350mg l-1TC,≥250mg l-1ALC,≥50mg/l CAL,≥300mg/l ARS for scales and≥350mg l-1TC,≥300mg l-1ALC,≥50mg/l CAL,≥200mg/l ARS for fin rays). In the presentinvestigation, the best mark quality (i.e., acceptable marks were observed in allsampled structures after immersion marking) were obtained with TC between350–500mg l-1, ALC between300–400mg l-1, CAL between150–250mg/l, and ARSbetween300–500mg/l. In addition, there was no significant difference in survival andgrowth conditions of marked fish compared to controls60days post-marking (p>0.05).2. In this study, external and internal morphological characters of fourhatchery-reared populations of Paralichthys olivaceus from Rizhao Shunyuan(RZSY), Rizhao Liangzhong (RZLZ), Weihai Shenghang (WHSH) and WendengXiaoguan (WDXG) were compared with one sea-caught population from Beihai ofWeihai (HBQT). The results showed that ambicoloration occurred on the blind side ofall Japanese flounder (100%) from four hatchery-reared populations, but the skin ofsea-caught flounder was normal. The hatchery-reared flounders had fused vertebraand the frequency of specimen was34.1%. On the contrary, fused vertebra neverappeared in sea-caught flounders. Fourteen morphometric characters of fivepopulations were analysed by PCA (principal component analysis), clustering anddiscriminant methods. The results of PCA and clustering analysis showed thatindividuals from WHSH and WDXG were pooled into one group, while individualsfrom other three sites were pooled into another group. According to the result ofprincipal component analysis, four principal components were constructed by factorloading, in which the first principal component was affected by ED/HL, EI/HL,BVL/BL and VPL/BL. The contribution ratios of four principal components were37.00%,18.92%,12.55%and7.68%, respectively, and the cumulative contributionratio was76.15%. In discriminant analysis, the total accuracy of discrimination onJapanese flounder from five populations was96%. HBQT was the lowest,92.9%, while WHSH was the highest,100%. Fourteen morphometric and eight meristiccharacters of five populations were analysed by one-way ANOVA. The resultsshowed that significant differences existed in ED/HL, EI/HL, doral fin rays, caudalfin rays and the number of vertebra among the five populations, and the differencesbetween hatchery-reared populations and sea-caught were extremely significant.Theresults of this study enrich the morphometric database of Japanese flounder betweendifferent groups, and provide basic references for new morphometric markingmethods, and for correctly assessing the effectiveness of Japanese flounder stockenhancement for fishery management.3. As part of the stock enhancement research project of Shandong Province, China,plastic oval tags (POTs) were used to mark juvenile Japanese flounder for release,Paralichthys olivaceus (70–133mm total length, TL), in2009and2010. Optimal tagplacement locations, retention, tagging rates, and mortality were initially evaluated.mark–recapture experiments were carried out in the coastal waters of Weihai City tostudy their migratory movements:21,202individuals in July2009at Beihai and18,350individuals in July2010at Lidao. The number of recaptured individuals were434(2.05%recapture rate) in2009and620(3.38%recapture rate) in2010. Aradiative movement from the release site was observed in the2009experiment;however, the tagging experiment showed a predominantly northward dispersal oftagged flounder from the release site in2010. The mean movement speed of thereleased fish was calculated as0.46km day-1in2009and1.05km day-1in2010.Furthermore, in2009, the average TL and wet mass increments were36.3±8.4mmmonth-1and27.13±16.09g month-1, respectively,1–6months after releasing;however, the increments were14.7±8.8mm month-1and5.65±4.17g month-1,respectively, in2010.4. To increase survival rate in stock enhancement of Japanese flounderParalichthys olivaceus, the substrate selection behavior and effect of starvation ondiet shift from extruded pellets to live mysids were investigated under laboratory conditions. In the present investigation, the results of substrate selection behaviorclearly indicated that juvenile flounder had obvious selectivity for the substrate ofgrain sizes GS <2.0mm, and the burying rates of fish at the sides of those substrateswere more than94%. The results of effect of starvation on diet shift showed thatstarvation had a positive effect on diet shift, and the “turning point†appeared whenthe juvenile flounder were deprived of food for about84hours. Additionally, in thestock enhancement of Japanese flounder the starvation through duration of handlingstress before released were controlled about36to84hours, thus the starvation couldfacilitate the transformation of food and could also reduce or avoid themortality caused by overlong starvation. Overall, it is suggested that appropriatesubstrate grain size should be considered before mass releasing, and a mild starvationmay benefit the process of diet shift. |
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