博士 / 國立臺灣大學 / 漁業科學研究所 / 91 / ABSTRACT
Cannibalism is an intraspecific predation. Cannibals kill and consume the entire or major part of a conspecific individual. This behavior is widespread in the animal kingdom, from lower protozoa to higher primates. In teleosts, the occurrence of cannibalism has been identified in at least 36 families. Cannibalism takes place at various ages; however, it is more intense among fast-growing larvae and juveniles than among adults. In Epinephelus groupers, intracohort cannibalsim usually results in mass mortality during larviculture. In the present study, we used orange-spotted grouper, E. coioides, as a model animal to study the cannibalism during grouper larviculture.
Based on measurements of mouth width, body depth, and total length (TL), a model of prey length (mm) to cannibal length was constructed: TLprey = 0.80 TLcannibal — 1.50, and the equation was confirmed by pairwise experiments. Furthermore, a multiple logistic regression model from the data of the pairwise experiments was developed to estimate the probability of cannibalism among different sizes of prey and cannibals:
P = 1/1+e -(0.1969CA-0.4021PR+3.811)
Based on these, I suggested that 30% is a threshold for TL differences to use in grading grouper fry, and that beyond the threshold, potential cannibals should be removed.
The effects of environmental factors such as feeding time, feeding frequency, kind of food and shelter on cannibalism rate were invesigated. The results indicated that only the factor of feeding frequency showed significant influence on cannibalism rate. Higher frequencies (3-4 times daily) significantly decreased cannibalism rate than did lower frequencies (1-2 times daily). Feeding frozen minced fish meat was more effective than artificial diet and frozen minced shrimp in suppressing cannibalism, but the differences among the three groups were not significant (P > 0.05). On the other hand, feeding time and shelter did not show significant effect on cannibalism rate.
Tryptophan (TRP) is a precursor of serotonin (5-HT), which is known to affect aggression in vertebrates, including fishes. Since cannibalism can be viewed as aggressive behavior, I designed a feeding experiment to test whether supplementary dietary TRP can effectively reduce the cannibalism in grouper fries. After 10 days of experiment, we found that TRP-supplemented diets were effective in increasing the levels of 5-HT in the brains of groupers by HPLC-EC analysis. TRP supplementation resulted in slightly lower cannibalism rate than in control without supplementary dietary TRP. However, body weight and total length of TRP groups were significantly smaller than those of the control. The results indicated that cannibalism among grouper fries could be mitigated by the oral administration of TRP, in addition or in place of environmental factors, and the recommendation on supplementary TRP level to be used is 0.5% of dry diet.
To sum up, size difference significantly intensified the cannibalism rate on grouper fry. Thus, routine grading by size according the criteria suggested by the study is necessary for grouper larviculture. In addition, higher feeding frequencies (3-4 times daily) and TRP-supplemented diet (0.5% of dry diet) significantly reduced occurrence of cannibalism. I think that the techniques should produce much better effects in decreasing cannibalism while they are combined with each other.
| Identifer | oai:union.ndltd.org:TW/091NTU00451002 |
| Date | January 2002 |
| Creators | Jinn-Rong Hseu, 許晉榮 |
| Contributors | Pung-Pung Hwang, 黃鵬鵬 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 107 |
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