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[1998 Naga Award Competition]

The ICLARM Quarterly
July - September 1999, Vol. 22, No. 3


     There are millions of children around the world who seldom have the opportunity to enjoy fresh and nutritious seafood as the young girls on the cover are doing. In fact many of them have diets that are low in nutrition, even when they do get enough to eat. Aquaculture holds great promise for increasing the availability of affordable food, protein and nutrients for human consumption and a healthier future for these children.

     Aquaculture has already been very successful towards increasing the supply of fish and now supplies nearly 30% of the food fish consumed worldwide. The scientific advancements in aquaculture have led  many analysts to write about a ‘blue revolution’.

     However, at what costs will aquaculture grow? Some of the environmental costs have already been realized and some are still unknown. On the other hand, eco-friendly aquaculture has also been shown to exist. The development and expansion of aquaculture must be and can be balanced with the need to protect the integrity of existing ecosystems. The introduction of new organisms or breeds into aquatic ecosystems can sometimes have negative consequences. It is important to study and assess the possible unintended effects before the introduction of a new species, especially if it is likely to affect biodiversity.

     This issue of the Naga has comments on three very different experiences of introductions of exotic aquatic organisms. One is an example of the successful creation of a whole new food industry with no negative side effects (the tilapia in Sri Lanka) and one that has had severely negative consequences (the golden apple snail in Japan). The third one highlights a potentially interesting situation for a case study on the adaptability, heritability, taxonomy and genetic variability of the rainbow trout in a number of distinct populations that have developed through successive introductions over the last century into a game fishery in India. This microcosm of the rainbow trout in the Nilgiri streams can provide useful information on the genetic profile and taxonomic status of an important aquaculture species that could be exploited on a larger scale for human consumption.

     As an important element of its work, ICLARM focuses on the development of sustainable aquaculture that will directly benefit poor people in developing countries. Both in Africa and Asia we have carried out research on resource flows on small farms to increase their productivity by integrating aquaculture into the system and using farm resources and wastes more efficiently. Considerable research and extension work has gone into developing inexpensive techniques for small farmers to raise fish in their household ponds and other unused seasonal waterbodies, like ponds, ditches and canals. Raising fish in ricefields has demonstrated benefits for rice productivity as well as providing fish to eat and sell. At a somewhat different level, a high yielding strain of the tilapia has been developed through selective breeding techniques. It promises a significantly higher output of this fish that is native to Africa but is now widely farmed in Asia, Latin America and the Caribbean. This research also provides a methodology that can be applied to other species for developing more productive strains of fish for culture. Marine aquaculture of giant clams, tropical sea cucumbers and pearl oysters is being researched and established at the village level in the Solomon Islands. Our scientific and technical research and developments are based on people’s needs and accessibility to resources so that the benefits to poor producers and consumers are maximized.


The Introduction of Exotic Fish in Sri Lanka with Special Reference to Tilapia
E. R. A. de Zylva


Introductions of exotic finfish between 1948 and 1953 are reported in this paper, with a brief reference to earlier and later introductions. Exotic fish were introduced principally to develop the potential for aquaculture in fresh and brackish waters in order to increase the availability of fish for rural communities through the biological control of aquatic vegetation. The algal feeding tilapia has created a new food industry in inland and brackishwaters. It has supplemented marine fishery production in a community where animal protein intake consists mainly of fish. It is also being cultured in flooded rice fields and used in the control of malaria. This excellent table fish has not had any adverse environmental impact.

E.R.A. de Zylva is a Fisheries Consultant and Adviser on Asian aquaculture training and development programs. Address: 30/70 Kensington Drive, Taradale 4001, New Zealand. Email: raydezylva@xtra.co.nz

Impact of the Introduction of Apple Snails and Their Control in Japan
Y. Yusa and T. Wada


The apple snail, Pomacea canaliculata, was imported into Japan and cultured extensively for food in the early 1980s. Not long after, escaped or discarded snails became feral and started feeding on rice seedlings and other aquatic plants. This was especially noted in Kyushu in southern Japan. Snails are still proliferating, but the area of damaged rice is not increasing as fast, mainly because of the success of snail control. Currently, the most effective methods of avoiding damage to rice are keeping water shallow, transplanting older seedlings and, in some cases, using molluscicides or repellents. However, these methods have almost no effect on damage by snail feeding when rice fields are flooded.
The apple snail is believed to be the most important obstacle to the spread of direct-sowing culture of rice in Kyushu. The Ministry of Agriculture, Forestry and Fisheries has launched a national project for the integrated management of the snail under direct-sowing rice culture. Some recent results from this project are briefly reviewed in this paper.

Y. Yusa and T. Wada are from the Kyushu National Agricultural Experiment Station, Nishigoshi, Kumamoto 861-1192, Japan.

Network of Tropical Aquaculture Fisheries Professionals (NTAFP) Section

Aquabyte (Aquaculture Section of NTAFP)


     Scientists are becoming more vocal about the need for conservation of aquatic resources that are increasingly under threat. The potential for aquaculture of a large number of species has yet to be assessed. However, their importance in capture fisheries should not be underestimated. A paper in a previous issue highlighted the importance of small size indigenous finfish as a valuable source of calcium, iron and vitamin A in Bangladesh. This issue has an article that highlights the decline in the availability of indigenous small fish to the rural poor as a result of agricultural intensification and the resultant habitat loss. It indicates a need for developing aquaculture of these species to protect this important source of nutrition for the rural population.

     Introduction and reintroduction of exotics to increase production from aquaculture operations is going on in many countries with little or no concern for the impact of these introductions on the environment and biodiversity. The paper from India suggests a strategy for management and reintroduction of exotics based on ecological and genetic data.

Dr. M.V. Gupta

Conservation of the Nilgiri Rainbow Trout in India
A. Gopalakrishnan, K.K. Lal and A.G. Ponniah


Rainbow trout is one of the important exotic species that is well established in the upland waters of India. This paper presents the historical background of its introduction and the present status of the fish in the streams of the Nilgiri peninsula of India. The rainbow trout inhabits natural reservoirs and streams of the region as a self recruiting population. The growth rate is reported to be relatively low and conflicting views about its taxonomic status have been reported. Successful crossbreeding of the Nilgiri rainbow trout with trout stocks from the Indian state of Himachal Pradesh has indicated the scope for utilizing cryopreserved milt as a mode of introducing new genetic material into the Nilgiri rainbow trout population. This paper outlines the requirement of ecological and genetic data to develop a strategy for management and reintroduction of fresh stocks.

A. Gopalakrishnan, K.K. Lal and A.G. Ponniah are from the National Bureau of Fish Genetic Resources (NBFGR) 351/28, Dariyapur, Talkatora Road, P.O. Box No. – 19 Lucknow 226 004, U.P., India.

Developing Aquaculture of Small Native Species (SNS) in Bangladesh: Village Level Agroecological Change and the Availability of SNS
D. Mazumder and K. Lorenzen


Small native species (SNS) of fish are an important source of protein and income for rural people in Bangladesh. A rapid rural appraisal study was carried out to explore recent changes in the availability of SNS in relation to agroecology and related issues. Village residents noted that the availability of SNS had declined drastically due to habitat loss related to agricultural intensification and due to the restriction of access to the remaining habitats in the course of aquaculture development. Their perception was that poor people had gained from the intensification of agriculture in terms of rice consumption but had lost in terms of reduced access to fish and other animal products.

D. Mazumder is a Research Associate at ICLARM, Road no. 7, House no. 75, Block-H, Banani, Dhaka-1213, Bangladesh. 
K. Lorenzen is Lecturer in Freshwater Fisheries at the Huxley School of Environment, Earth Sciences and Engineering, Imperial College, 8 Princes Gardens, London SW7 1NA. 

Fishbyte (Fisheries Section of NTAFP)


“Progress in any field depends primarily on our ability to synthesize previous experience”. This is the opening remark from Hilborn and Liermann’s recent plea for meta-analysis in fisheries, published in a Beverton and Holt Jubilee (40 years young) special issue of Reviews in Fish Biology and Fisheries. Ray Hilborn and Martin Liermann emphasize that fisheries models should strive to incorporate experience and not simply ignore it as most often the case. They find comfort, however, in the pioneering compilations of Daniel Pauly on natural mortality, in Ram Myers and colleagues' stock-recruitment work, and they conclude that the most critical need for meta-analysis is availability of databases, citing FishBase (www.fishbase.org) as a good example. Another good example is given in this issue of FishByte. Tom Brey of AWI has for years been collecting and analyzing information on productivity of benthic invertebrates and his Opus Major from 1995 is indeed a gold mine for ecological modelers in need of reliable productivity estimates. We are happy to present a Brey potpourri of empirical relationships here. As ecological modeling is becoming more and more useful for fisheries research, the need for information on all aspects of aquatic life is increasing. Reflective of this is that we are including a variety of empirical relationships in the Ecopath with Ecosim software system (www.ecopath.org) and welcome more inputs from you.

                                                                                                      G. Silvestre and V. Christensen
A Collection of Empirical Relations for Use in Ecological Modelling
T.  Brey


This study summarizes previously published and updated empirical relations for the estimation of production/biomass ratios in benthic invertebrates; of natural mortality in benthic invertebrates and finfish; and of respiration from production and vice versa in animal populations. A MS-EXCEL spreadsheet containing these equations is available from the author via Email. They are also included in the Ecopath with Ecosim software.

T. Brey is from the Alfred Wegener Institute for Polar and Marine Research, P.O. Box 120161, D-27576, Bremerhaven, Germany. Email: tbrey@awi-bremerhaven.de

Escalation in Shrimp Production in the Sierra Leone Industrial Fishery
P.A.T. Showers


Applying Tukey's jackknife method on MSY estimates from the surplus production models of Schaefer and Fox showed that the optimum yield for shrimps in industrial fishery in Sierra Leone is estimated at 2686.8 t with 15822 fishing days.  Annual catch for 1996 was 2788 t, indicating an escalation in exploitation which, if prolonged, could bring reduced productivity as experienced in the fishery some years ago.

P.A.T. Showers is from the Institute of Marine Biology and Oceanography, Fourah Bay College, University of Sierra Leone, Sierra Leone.

Growth and Length-Weight Parameters of Pacific Mackerel (Scomber japonicus) in the Gulf of Guayaquil, Ecuador
E. Cucalón-Zenck


The seasonally oscillating growth parameters and length-weight relationship for Scomber japonicus caught in the Gulf of Guayaquil, Ecuador, were determined based on length-frequency data from 1989 to 1996, using the FiSAT software package of Gayanilo et al. (1996). Estimates of growth parameters are in general agreement with previous studies on the same species. Results also imply that the growth of S. japonicus slows down during the cold season by approximately 50% with respect to the average growth. The mean value of the power b is significantly larger than 3, indicating that the model of allometric growth should be used for the length-weight relationship and calculation of the condition factor.

E. Cucalón-Zenck is from Oceanografia y Pesca Consultores (Fisheries and Oceanography Consulting)PO Box 09-01-4382, Guayaquil, Ecuador. Email: ecucalon@gu.pro.ec