棕點石斑育苗技術開發:影響殘食及成長因子之探討

Abstract

石斑魚屬高價魚類且廣受世界各國喜好，隨著亞洲區域華人經濟興起，石斑的消費量不斷攀升，可說目前為亞洲養殖的黃金魚種，為提升養殖技術及石斑養殖種類之多樣性，本試驗以棕點石斑魚苗進行育成試驗研究，並針對殘食行為及魚苗放養密度與投餵頻率進行探討。育成試驗以室內循環水系統進行培育工作，水源及器具均經過消毒殺菌以隔絕病源之侵害，配合良好之管理及投餵優質飼料使魚苗穩定成長。育成試驗結果顯示最佳之活存率可達91%，其死亡之主因皆為殘食所造成，於飼養過程中並無疾病傳染，表示透過完善之管理可避免疾病爆發使魚苗穩定健康成長。為降低殘食所造成之傷亡，需得知魚苗體型差距多大時容易誘發殘食發生，再適時配合篩網分級以降低其差距。為得知棕點石斑魚苗發生殘食時之大小魚之體型差距，經由測量魚體型態數殖可建立一殘食者(cannibal)與被殘食者(prey)之關係式: TL(prey) = 0.68TL(cannibal) + 5.36，可得知當棕點石斑魚苗在體長20~80mm時其大小魚體型差距達1.10~1.33倍時殘食即容易發生，故該方程式可方便日後輸入大小魚之體長即能得知殘食是否容易發生，進而評估篩網使用之適當時間以降低殘食發生機率。投餵頻率與放養密度之試驗中顯示，魚苗大小為4公分之階段，投餵頻率為每日6餐放養密度維持30~50尾/L時有較佳之活存率、增重率、攝食率及體型差異，於低密度組5尾/L之組別容易使魚苗產生領域性、攝食強度不足，且有容易受驚嚇之現象，提高放養密度則可促使魚群群聚進而增加攝食，有效增加飼料之利用並縮短投餵所耗費之時間。 綜合試驗結果顯示，以完善之環境及管理可使棕點石斑苗穩定成長，並降低疾病爆發之機會，於育苗過程中適度提高投餵頻率及養殖密度可提升養殖之成效，而當魚群體型差異超過殘食發生之閥值時，可配合篩網分級飼養以降低殘食行為發生。結合各項因子期以提高棕點石斑魚苗活存率、減少天然資源損耗及降低養殖成本，進而增進石斑產業競爭力。

The grouper, which is the most valuable fish, has been very popular all over the world, especially in Asia. In order to improve the aquaculture technology for different groupers, the purpose of this work is to study the fingerling rearing techniques of tiger grouper Epinephelus fuscoguttatus, especially focusing on cannibalistic problems, the most suitable feeding frequency and stocking density. An indoor recirculation system was adopted as the experimental environment in this study. The water and instruments were disinfected, as well as offering good-quality feed, so as to reduce the influences of virus and other harmful factors. The results of rearing experiments reveal that the highest survival rate was 91%, and that the main reason of death was cannibalism. Besides, there was no disease in this process because we always kept a high-quality rearing environment and took care of everything from the very beginning. In order to reduce the death toll of fingerlings because of cannibalism, we have to understand the relationship between the cannibalistic problem and the body-size difference. According to the results of this study, the relationship between the cannibal and prey could form an equation: TL(prey) = 0.68TL(canni) + 5.36. Based on this equation, we could realize that the cannibalistic problem will occur most frequently when the body-size difference reaches 1.13-1.33 times. Thus, this equation could be used to predict the possibility of cannibalistic problems, and could help the fish-keeper determine when to separate different body-size tiger groupers. In the other experiment, we focused on the most suitable feeding frequency and stocking density. Based on the results, we concluded that the best feeding frequency is 6 times per day, and the best stocking density is 30-50 fishes/L. Interestingly, groupers tended to be territorial, easily frightened and not appetitive in lower stocking density (5 fishes/L). We therefore suggest that high stocking density might be beneficial for tiger groupers’ fingerling rearing. In conclusion, it’s of importance for grouper-keepers to maintain high-quality rearing environment in order to reduce the risk of the disease and virus-infection. Additionally, it might also be beneficial to moderately increase the feeding frequency and stocking density during the fingerling rearing process. If the body-size difference exceeded the threshold of cannibalism, classifying and separating different body-size fishes is one of effective approaches to reduce the cannibalism.