Growth and reproduction of Cyclopina kasignete and its application as a potential live food for fish larvae

Author: Wan Nurul Nadiah Wan Rasdi

Wan Rasdi, Wan Nurul Nadiah, 2016 Growth and reproduction of Cyclopina kasignete and its application as a potential live food for fish larvae, Flinders University, School of Biological Sciences

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Copepods are common natural food for most fish larvae in the ocean, and fish larvae require live feed with adequate nutrition to be successfully reared in a hatchery. This thesis studied the reproductive biology, population growth and nutritional requirement of the cyclopoid copepod Cyclopina kasignete and further tested its use as a live food for fish larvae. Four experiments were performed to investigate (1) the improvements of algal nutritional quality by manipulations of nitrogen and phosphorus in the medium, (2) the beneficial use of dietary algae in modifying the nutritional content and digestive enzymes in copepods, (3) the potential use of enriched algae to improve the population growth and reproduction of copepods, and (4) the use of copepod as live food for feeding larval fish, the Asian seabass Lates calcarifer.

In experiment 1, algae cultivated with N:P ratios of 20:1 and 30:1 showed favorable algal growth and increase in protein content, while the high N:P ratio (120:1) reduced algal growth and protein content but increased lipid contents in algae. The N:P ratio of 20:1 increased the EPA content in Nannochloropsis oculata while the N:P ratio of 30:1 increased the DHA content in Tisochrysis lutea. The knowledge of using appropriate N:P ratios for algal culture in this study can be applied in a hatchery to produce algae with superior quality which in turn enhances nutritional profiles in copepods.

In experiment 2, the highest protease and trypsin enzymes in copepods were detected when fed with dried Melosira sp. and fresh T. lutea. The amounts of fatty acids and digestive enzymes in copepods can be modified by feeding the copepod with different dietary algae because even with low contents of EPA, DHA and ARA in the dried Melosira sp. and mixed dry algae, C. kasignete showed higher EPA, DHA and ARA when fed these corresponding diets than other diets.

In experiment 3, the diatom Melosira sp. was used as either a single or a mixture with other algae to sustain the growth and reproduction of C. kasignete. The superior diets (dried Melosira sp., fresh N. oculata, and fresh T. lutea) were tested as a single or in a combination diet in the copepod culture. The C. kasignete produced maximum growth and offspring production when fed the monoalgal diet of dried Melosira sp. or the binary diets of dried Melosira sp. and fresh T. lutea. Experiments 2 and 3 showed that C. kasignete contained high EPA, DHA, protease and trypsin after feeding on enriched algae and these nutritional components are essential for fast growth and reproduction in copepods.

These findings on copepods led to the study of experiment 4 where Lates calcarifer larvae were fed with conventional live foods rotifers and Artemia along with C. kasignete. Larval fish showed better growth and survival when fed with live foods with copepod supplementation, suggesting that the improved nutritional profiles in copepods enhanced the growth and survival of fish larvae. Experiment 4 clearly indicates that the use of this copepod for Asian seabass culture can improve fish growth, survival and fatty acid contents of fish larvae.

In summary, the manipulation of nitrogen and phosphorus ratios in the culture media can improve the quality of algae as a live food for copepods, which in turn can improve the fatty acids and digestive enzymes in copepods. Copepods can then provide the necessary nutrients to larval fish to improve the growth and survival of fish larvae.

Keywords: algae, copepods, nutritional manipulation, enrichment, live feed, fish, aquaculture

Subject: Biological Sciences thesis

Thesis type: Doctor of Philosophy
Completed: 2016
School: School of Biological Sciences
Supervisor: Professor Jian Qin