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from both the primary producers and protein-enriched detritus.
Results from a Venezuelan lake suggest that the influence of detritus may be even more far-reaching than has been suggested here. Bowen (1980) has analysed detritus and reported that it contains significant quantities of a range of non-protein amino acids. On the basis of this finding, and on investigation of the physiology of the fish's alimentary canal, he attributed the rapid growth of tilapia to assimilation of non-protein detrital amino acids. Obviously this subject would repay investigation in the case of other fish and shrimps (vide Table 5).
In any event, removal of the mangroves from around the kei wais would remove the main source of detritus and thus lead to diminishing productivity of the kei wais. This points up the practical importance of maintaining the mangrove community.
A kei wai, such as No. 7, gives a reasonable return of economic produce which is both varied in kind and distributed throughout the year. The actual financial return depends on the amount of rent paid to the landlord; in some cases this may be so high as to make the operation financially unattractive. Given the periodic nature of the work, operation of kei wais would seem to be best suited to a small cooperative which owned the freehold.
Acknowledgements
Most of this work was carried out during the period June-December 1978 when C.Y.H., K.Y.T. and S.W.T. were employed under the Summer-work programme of the Agriculture and Fisheries Department; we wish to thank the Director for arranging that financial support. In addition, we wish to thank Mr. Chan Sau and Mr. Wong Chiu for allowing us to investigate conditions in the kei wai and for answering our many questions so helpfully. Our thanks are due also to Mr. Lau Sin Pang, Mr. D.S. Melville, and Mr. Wong Pak Hei, all of the A.F.D., for their advice and help in carrying out the project, and to Dr. Chan Kwong-yu for kindly advising us on bacteriological methods. We acknowledge, with thanks, Mr. Melville's permission to use two photographs taken by him.
201
from both the primary producers and protein-enriched detritus.
Results from a Venezuelan lake suggest that the influence of detritus may be even more far-reaching than has been suggested here. Bowen (1980) has analysed detritus and reported that it con- tains significant quantities of a range of non-protein amino acids. On the basis of this finding, and on investigation of the physiology of the fish's alimentary canal, he attributed the rapid growth of tilapia to assimilation of non-protein detrital amino acids. Obvi- ously this subject would repay investigation in the case of other fish and shrimps (vide Table 5).
In any event, removal of the mangroves from around the kei wais would remove the main source of detritus and thus lead to deminishing productivity of the kei wais. This points up the prac- tical importance of maintaining the mangrove community.
A kei wai, such as No. 7, gives a reasonable return of economic produce which is both varied in kind and distributed throughout the year. The actual financial return depends on the amount of rent paid to the landlord; in some cases this may be so high as to make the operation financially unattractive. Given the periodic nature of the work, operation of kei wais would seem to be best suited to a small cooperative which owned the freehold.
Acknowledgements
Most of this work was carried out during the period June-De- cember 1978 when C.Y.H., K.Y.T. and S.W.T. were employed under the Summer-work programme of the Agriculture and Fish- eries Department; we wish to thank the Director for arranging that financial support. In addition we wish to thank Mr. Chan Sau and Mr. Wong Chiu for allowing us to investigate conditions in the kei wai and for answering our many questions so helpfully. Our thanks are due also to Mr. Lau Sin Pang, Mr. D.S. Melville and Mr. Wong Pak Hei, all of the A.F.D., for their advice and help in carrying out the project, and to Dr. Chan Kwong-yu for kindly advising us on bacteriological methods. We acknowledge, with thanks, Mr. Melville's permission to use two photographs taken by him,
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