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The ICLARM Quarterly
January - March 2000, Vol. 23, No. 1


Behind the Beautiful Fish in an Aquarium

    We all enjoy the sight of colorful fish and corals in an aquarium and marvel at the beauty and splendor of life hidden in the oceans. But we do not often stop to think of the diverse range of services these living aquatic resources provide, in their natural settings, to the planet and its people. Knowledge of the vast biological diversity of the oceans is still very limited, even though we are using their biological resources to satisfy many human needs – the most basic being food.
  The tropical marine aquarium industry is expanding by 10-15 percent annually. A typical scenario is illustrated in the Solomon Islands where women and men from coastal villages catch ornamental fish from reefs using hand held nets. About 150 species of fish are caught and exported. They also export about 30 species of hard and soft corals and six species of giant clams. So the aquarium not only provides us a glimpse of beautiful ocean life, it also provides a living to such poor coastal communities. However, resort owners, divers and tourists worry about the possible loss of the recreational amenity of these beautiful fish and corals, and scientists are concerned about the irreversible loss of biodiversity and damage to coral reef habitats, especially in locations where blast fishing and other such destructive practices are prevalent. Coral reefs and their surrounding environments have been recognized as one of the most productive resource systems on earth. They support a quarter of all known marine species and an estimated one million or more as yet undocumented. 
    Clearly, destructive fishing practices need to be stopped. But even in situations where such practices are not used, it is necessary to ensure that the harvests are not greater than the natural rate at which these species can replenish themselves. At the same time the livelihood of coastal villagers, who have few alternative earning opportunities, is at stake. It becomes important to balance the needs of the poor whose livelihood depends on these resources, the interests of the traders whose business depends on them, the interests of the resort owners who earn a living from tourists and divers, and the interests of all of us who value and need the biodiversity of natural resources.
    Management of these resources based on scientific knowledge can provide a solution for these opposing forces. This knowledge would include the rate of natural replenishment of species collected from coral reefs, how the magnitude and frequency of harvesting affects this, and how the coral colonies recover from ‘cuttings’ taken for farming. Biological and ecological studies can help to make an assessment of the maximum sustainable harvest for different species. They can also help to develop marine aquaculture for many species to reduce the pressure on natural stocks.  For example, in the Solomon Islands giant clams can be cultured for harvesting and for adding to wild stocks. Such knowledge should form the basis of management regimes to regulate and support a sustainable and non-destructive use of these valuable resources.
    Science is crucial to the formulation of effective policies for the sustainable use and management of aquatic resources – a major potential source of food, medicines and livelihood for the human race.

Rita Kapadia


Integrating Fish and Azolla into Rice-Duck Farming in Asia
A.G. Cagauan, R.D. Branckaert and C. Van Hove


Several countries in Asia practice integrated rice-duck farming. On-farm resources such as duck manure and feed waste are not adequately used and recycled in the system. This indicates the potential for research to increase the productivity of the rice-duck system. The integration of fish and the nitrogen-fixing aquatic fern azolla show promise for increasing the production potential of the system. Fish, azolla and ducks integrated with rice farming can result in nutrient enhancement, pest control, feed supplementation and biological control. Some of the results of a case study on integrated rice-fish-azolla-duck farming systems conducted in the Philippines are presented in this paper.

A.C. Cagauan is from the Freshwater Aquaculture Center, Central Luzon State University, Muñoz, Nueva Ecija, Philippines, and is presently a Research Fellow supported by the International Development Cooperation, Catholic University of Louvain, B-1348 Louvain-la-Neuve, Belgium; R.D. Branckaert is from the Animal Production and Health Division, Food and Agriculture Organization, Rome, Italy (e-mail: Rene.Branckaert@fao.org); C. Van Hove is from the Unit of Plant Biology, Catholic University of Louvan (e-mail: vanhove@bota.ucl.ac.be).

Floating Islands: a Unique Fish Aggregating Method
V.R. Suresh


A fish aggregating device made of aquatic weeds and grass (Phoom) is used in Loktak lake in the northeastern region of India. It has been used successfully in this very productive fishery for centuries. Today, the fishery itself is under pressure from overexploitation, soil erosion leading to siltation and a hydroelectric project that has blocked the migratory route of the fish that used the lake as a breeding ground.

V.R. Suresh is from the ICAR Research Complex for North Eastern Hill Region, Manipur Centre, Imphal - 795 004, India. 

Network of Tropical Aquaculture Fisheries Professionals (NTAFP) Section

Aquabyte (Aquaculture Section of NTAFP)

River-based Artificial Propagation of the African Catfish Clarias gariepinus: an Option for the Small Fish Farmer
H. Charo and W. Oirere


A cheap method of propagating the African catfish, Clarias gariepinus, by incubating the fertilized eggs in a cage placed directly in a flowing river is described. Hatching ranged between 39 and 70%. This is not significantly different from the commonly used water recirculating flow through system. The economic advantages of the river hatching method are discussed with special emphasis on the rural fish farmers.

H. Charo and W. Oirere are from the KMFRI-Sangoro Research Centre, P.O. Box 136, Pap-Onditi, Kenya. 

Bioconversion Efficiency and Growth in the White Shrimp, Penaeus indicus (Milne Edwards), Fed with Decomposed Mangrove Leaves
S. Athithan and V. Ramadhas


Food conversion efficiency and growth in the white shrimp Penaeus indicus fed with decomposed mangrove leaves of Avicennia marina and A. officinalis were monitored under laboratory conditions. It was observed that test animals fed with the decomposed leaves of A. marina had higher assimilation efficiency (87.96%), gross growth efficiency (10.82%), net growth efficiency (12.3%) and relative growth rate (0.0603 g/day) than those fed with A. officinalis. The relatively higher growth registered in the animals fed with decomposed leaves of A. marina was attributed to its high calorific and protein content.

S. Athithan and V. Ramadhas are from the Fisheries College and Research Institute, Tuticorin - 628 008, India. 

Fishbyte (Fisheries Section of NTAFP)

Length-Weight Relationship of Marine Fishes from Southern Brazil
M. Haimovici and G. Velasco


The relationship between length (L) and weight (W) was estimated for 80 species belonging to 50 families of marine fishes from the shelf and upper slope of southern Brazil (lat. 28°S - 34°S). Sample sizes (n) for different species ranged from 11 to 14 741 specimens collected from commercial landings and research surveys. The fit of the equations (W=aLb) with a and b parameters estimated from regular and functional regression (of log-transformed weight and length data) as well as from a non-linear iterative process using the quasi-Newton algorithm were compared. The non-linear method gave the most accurate estimates in terms of residual sum of squares. Differences were less than 2.3% for n>500 compared with predictive regressions and 1.5% compared with functional regressions. No difference was observed between both predictive and functional regressions. Determination coefficients (r2) increased with sample size, and the highest r2 were obtained for 50<n<500, decreasing slightly for larger samples due to seasonal changes in the condition of the fishes.

M. Haimovici (docmhm@super.furg.br) and G. Velasco (pgobgvc@super.furg.br) are from Depto. Oceanografia, FURG. CX.P. 474, Rio Grande RS, Brazil, 96201-900.

Adaptive Response of Peruvian Hake to Overfishing
C. Wosnitza-Mendo and R. Guevara-Carrasco


Compensatory mechanisms of the Peruvian hake population (Merluccius gayi peruanus) in response to heavy exploitation and changes in species interaction are discussed. Changes in the rate of cannibalism, diet composition, maximization of fecundity and behavioral adaptation are noted.

C. Wosnitza-Mendo is from Pargue Bartolome Herrera 190, Lima 32 - Peru while R. Guevara-Carrasco is from the Instituto del Mar del Peru (IMARPE), Apartado 22, Callao, Peru. 

The Marine Fisheries of Jamaica
K. Aiken and G.A. Kong


The marine fisheries of Jamaica are almost entirely artisanal, with at least 15 000 fishers and an annual catch of approximately 7 000 t. A recent development is a small industrial fishery for queen conch and spiny lobster that earns significant foreign exchange for the country. The major aquatic resources are coral reef  fishes, conch, lobster, small pelagics and seasonal large pelagics. The major fishing grounds are the southern island shelf and Pedro Bank, a large oceanic bank 150 km to the southwest of Kingston. The fisheries are rated as overfished, except the queen conch fishery which is relatively well managed. A new Fisheries Bill is currently being reviewed with the intention of improving the efficiency of management measures and of fisheries administration. There are plans for rehabilitating the fisheries and developing them with a focus on their sustainability in the future.

K Aiken (kaaiken@mail.infochan.com) is a lecturer in the Department of Life Sciences, University of the West Indies, Mona campus. G. Andre Kong is the Director of Fisheries, Fisheries Division, Ministry of Agriculture, Kingston, Jamaica.