Nutrient Dynamics in Eutrophic Inland Waters Used for Aquaculture TABLE OF CONTENTS

Philippines
Thailand
Hong Kong

Based on the work of J. Barica

NUTRIENT DYNAMICS IN EUTROPHIC INLAND WATERS
USED FOR AQUACULTURE IN SOME COUNTRIES BORDERING THE SOUTH CHINA SEA, WITH PARTICULAR REFERENCE TO MASS FISH MORTALITIES

Proposal for monitoring programmes
(Philippines, Thailand and Hong Kong)

by

Jan Barica
Consultant

Project Document Identification

Work Plan Activity: 4(b) (iii) and (c) (i)

2. Determination of extent and nature of areas suitable for future expansion of aquaculture

   2. Describe ecological characteristics of the areas where expansion seems possible, e.g. vegetation, salinity, water quality, water currents, etc.

3. Examination of factors affecting productivity and profitability of existing and future aquaculture operations

   1. Examine general level of aquaculture practice, in particular aquaculture industries (e.g. milkfish, prawns) - e.g. fertilizing practices, quality of water, stocking practices, disease and predation control, harvesting, etc.

SOUTH CHINA SEA FISHERIES DEVELOPMENT AND COORDINATING PROGRAMME
Manila, March 1976

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TABLE OF CONTENTS

ABSTRACT

INTRODUCTION

PART I. PHILIPPINES
SEASONAL FISHKILL PROBLEM IN LAGUNA DE BAY

1. Background information

2. Study area (Laguna de Bay Lake)

2.1 Limnology and water quality

2.2 Fisheries, fishpen industry

3. Difficulties encountered in fishpen culture

3.1 Analysis of mass milkfish mortalities in Laguna de Bay: existing information

3.2 Similarities of the Laguna de Bay fish mortalities with summerkills in mid-western North America

3.2.1 The cause of summer fishkill

3.2.2 Selection of significant environmental parameters accompanying summerkills

3.2.3 Mechanism of a prairie summerkill

3.3 Possible remedial actions in North American conditions

4. Recommendations

4.1 Rationale

4.2 Selection of experimental pens

4.3 Monitoring programme

4.3.1 Weather information

4.3.2 Fisheries biology

4.3.3 Water quality sampling of selected fishpens

5. Conclusions

6. Other Activities

6.1 Milkfish mortalities in brackish water ponds in Iloilo Province

PART II. THAILAND
CATFISH MORTALITIES IN FARM PONDS

1. Background information

2. Intensive culture of catfish in small ponds near Bangkok

2.1 Biology and production

2.2 Management, water supply and water quality of the ponds

3. Recommendations

3.1 Rationale

3.2 Improvement of water quality in catfish ponds

3.2.1 Pond management

3.2.2 Water quality monitoring

4. Conclusions

5. Other Activities

5.1 “Green” fertilization of reservoirs - possibilities

5.2 Revision of coastal pollution proposal for Thailand

PART III. HONG KONG
FISH MORTALITIES IN POLYCULTURE FARM PONDS (MULLET-CARP)

1. Background information

2. Inland fish culture in Hong Kong

3. Water quality and fishkill problem in the ponds

3.1 Existing information

3.2 Probable cause of mortality

4. Recommendations

4.1 Rationale

4.2 Monitoring

4.3 Other studies

5. Conclusion

REFERENCES

APPENDICES

APPENDIX I Physico/chemical observations in selected Laguna de Bay fishpens

APPENDIX II Phytoplankton composition and approximate abundance of selected fishpens in Laguna de Bay

APPENDIX III List of research problems for Laguna de Bay and tributary rivers by the Coordinating Committee on Complementary Researches for the Laguna Lake Research and Development Program, National Science Development Board

APPENDIX IV Itinerary of Consultant and List of Institutions and Officers Contacted

NUTRIENT DYNAMICS IN EUTROPHIC INLAND WATERS USED FOR AQUACULTURE IN SOME COUNTRIES BORDERING THE SOUTH CHINA SEA, WITH PARTICULAR REFERENCE TO MASS FISH MORTALITIES

Proposal for Monitoring Programmes (Philippines, Thailand and Hong Kong)

Based on the work

of

Jan Barica*
Consultant

ABSTRACT

This paper describes the nutrient dynamics in selected inland waters used for aquaculture. It is based on field work in the Philippines, Thailand and Hong Kong during October/November 1975. Seasonal fishkills resulting in economic losses, were analysed. Based on the field work and available literature pertinent to the subject, proposals for monitoring programmes aimed at predicting fishkills in the areas visited were formulated.

^* Present address: Environment Canada, Fisheries and Marine Service, Freshwater Institute, Winnipeg, Manitoba

INTRODUCTION

Aquaculture accounts for a significant proportion of the fish and shellfish production in the countries bordering the South China Sea. While coastal brackish water aquaculture has a long and well-established tradition in some of these countries (Philippines, Indonesia), inland freshwater resources are more often used in others (Thailand, China). Expansion of aquaculture production to meet increasing demand for fish protein by rapidly growing population is possible in two ways: by extension of the present area under culture (both coastal and inland), or by increasing the productivity per unit area. An approach to the latter may be achieved through improved manipulation of primary production by addition or removal of plant nutrients, i.e. maintaining an optimum trophic status of aquaculture ponds or impoundments.

Despite a century long tradition in fish farming, very little is known about the relationship between water quality, phytoplankton production and fish producing capability of the region's aquatic resources. Nutrient dynamics, which determines the fundamental environmental conditions governing the primary, and thus the overall biological production, is not sufficiently understood, and the techniques of manipulating nutrient levels in order to increase fish production not developed. If inland water aquaculture is to supplement existing coastal practices successfully, more understanding is needed in this respect, as conditions in stagnant freshwater bodies with limited water exchange and dilution are susceptible to environmental imbalance and disturbances. Recent disastrous massive scale mortalities of pen-raised milkfish in Laguna de Bay lake in the Philippines, supposedly caused by noxious Microcystis bloom, showed a warning that nutrient level control and eutrophication abatement are crucial for the very existence of fish in freshwater bodies. On the other hand, proper fertilization, i.e. addition of basic plant nutrients in mineral or organic form for the optimum and manageable growth of algae can bring about a substantial increase in fish production as practised in less productive ponds all over the world.

This report is based on field visits by the author to three countries bordering the South China Sea (Philippines, Thailand and Hong Kong), on published and unpublished information obtained from discussions with local fisheries officers, biologists and entrepreneurs, as well as collected experimental material. The objective of this two-month mission was to: (1) specify some acute problems associated with nutrient regime supply and cycling and its impact on phytoplankton biomass and fish production, particularly mass fish mortalities in unbalanced ecosystems, and (2) formulate appropriate recommendations regarding future studies in this field, which could be followed up by local fisheries and environmental agencies. The observations and recommendations are listed in order of countries visited. Situations where water quality appears to play an important role in fish production are emphasized.