The relationships between cultivated fish species and their environment is largely dependent on the biological characteristics of the fish and the degree of intensification of the culture . In extensive and semi-intensive systems, based on natural production, stocking fish species of different feeding habits together enables a more efficient utilization of pond resources . In polyculture systems only a proper combination of ecologically different species at adequate densities will utilize the available resources efficiently, maximize the synergistic fish-fish and fish-environment relationships and minimize the antagonistic ones . Synergistic interactions among fish species may be explained on the basis of two interrelated processes : increase of food resources and improvement of environmental conditions . Antagonistic interactions occur between incompatible species combinations and when the stocking rates are unbalanced ; in this case, the way the system is affected depends on the food chain level were the imbalance occurs . Several examples of synergism and antagonism at different levels of the food chain are analyzed in this paper . The knowledge of fish-fish and fish-environment quantitative relationships enables choosing adequate combinations of fish species, stocking rates, input types and rates, and other management decisions according to the specific local conditions : climate, quality of water supply and pond fertility, availability of fish fry and fingerlings, availability of feeds and fertilizers, and market requirements . 177

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RESUMO -Dados sobre esforço e captura por espécie correspondentes à produção pesqueira desembarcada no porto de Santarém, no ano de 1993, foram submetidos a duas técnicas de análise multivariada: uma análise de fatores segundo o método de componentes principais e outra de covariância conforme o modelo linear geral (GLM). Os resultados indicam que a atividade pesqueira na região está influenciada pelas características dos ciclos de vida das espécies-alvo, pelo ciclo hidrológico e condição climáticas de sistema, e ainda pelas preferências culturais e interesses econômicos do mercado consumidor. Os resultados indicam o direcionamento da atividade pesqueira para determinados grupos de espécies, e as diferentes variáveis incluídas no modelo permitiram uma explicação aproximada dos padrões desse direcionamento. Esses padrões são: (a) pesca de grandes bagres, alvo de pesca para a exportação (FATOR 1); (b) pesca de entre-safra do mapará (Hypophthalmus spp.) e da pescada (Plagioscion spp.), realizada nos lagos com um componente para exportação e outro para o consumo local (FATOR4); (c) pesca de peixes de escamas de hábitos sedentários e/ou migratórios, alvo da pesca comercial de pequena escala e de importância no mercado local (FATOR2, FATOR3 e FATOR5), que inclui pescarias importantes como a do tambaqui (Colossoma macropomum) e do pirarucu(Arapaima gigas) nos lagos, ou a do jaraqui (Semaprochilodus spp.) e pacu (Mylossoma spp. e Metynnis spp.) nos rios.Palavras-chave: pesca artesanal, Baixo Amazonas, dinâmica da pesca. Artisanal Fishery in the Lower Amazon: Multivariate Analysis of the Catch by Species.ABSTRACT -Effort and catch data per species making up for fisheries yield landed in 1993 in the city of Santarém were submitted to two techniques of multivaliate analysis: a factor analysis by the principal components method and a covariance one using the general lineal model (GLM). Results suggest fishing activities in the region is influenced by the life cycle peculiarities of target species, by the water cycle and the weather conditions in the system, as well as by the cultural biases and economic interests of the consumer market. The results revealed the directioning of fishery activities toward certain groups of species, and those patterns were identified: (a) the fishing of large catfishes for export (FACTOR1); (b) the between-seasons fishing of mapará (Hypophthalmus spp.) and pescada (Plagioscion spp.) in lakes, with local and for export components (FACTOR4); (c) the fishing of sedentary and/or migratory scaled fishes, targeted by small-scale commercial fisheries with local importance (FACTOR2; FACTOR3 and FACTORS), which includes important catches such as tambaqui (Colossoma macropomum) and pirarucu (Arapaima gigas) in the lakes, or jaraqui (Semaprochilodus spp.) and pacu (Mylossoma spp. and Metynnis spp.) in rivers. Key-words: local fisheries, Lower Amazon, fisheries pattern INTRODUÇÃOA pesca artesanal na Amazônia brasileira é de vital importância para o fornecimento de alimento à população local e como fonte de ...

The e¡ects of introducing common carp (CC) and of adding arti¢cial feed to fertilized rohu ponds on water quality and nutrient accumulation e⁄ciency were studied. All ponds were stocked with 15000 rohu ha À1 . Treatments included ponds with rohu alone, rohu plus 5000 common carp ha À1 and rohu plus 10 000 CC ha À1 . A comparison was also made between supplementally fed and non-fed ponds. The overall highest nitrogen (N) and phosphorus (P) concentrations were observed in ponds with 5000 CC ha À1 , followed by ponds with 10 000 and 0 CC ha À1 . The largest fractions of N and P inputs accumulating in ¢sh, phytoplankton and zooplankton were observed in ponds with 5000 CC ha À1 , followed by ponds with 10 000 CC ha À1 and subsequently ponds without CC. Relatively more nutrients accumulated in benthic organisms in ponds without than in ponds with CC. A smaller fraction of the nutrient input was retained in ¢sh, plankton and benthic organisms in ponds without CC compared with ponds with CC. Compared with 5000 CC ha À1 , stocking10 000 CC ha À1 can be considered as overstocking, because this leads to lower ¢sh production and relatively less nutrients retained in plankton and benthic organisms.

A participatory on‐farm study analysed water and nutrient budgets of six low and four high water‐exchange ponds of integrated agriculture–aquaculture (IAA) farms in the Mekong delta. Water, nitrogen (N), organic carbon (OC) and phosphorus (P) flows through the ponds were monitored, and data on fish production and nutrient accumulation in sediments were collected during a fish culture cycle. Results showed that, on average, only 5–6% of total N, OC or P inputs introduced into ponds were recovered in the harvested fish. About 29% N, 81% OC and 51% P accumulated in the sediments. The remaining fractions were lost through pond water discharges into adjacent canals. Fish yields and nutrient accumulation rates in the sediments increased with increasing food inputs applied to the pond at the cost of increased nutrient discharges. High water‐exchange ponds received two to three times more on‐farm nutrients (N, OC and P) while requiring nine times more water and discharging 10–14 times more nutrients than the low water‐exchange ponds. Water and nutrient flows between the pond and the other IAA‐farm components need to be considered when optimizing productivity and profitability from IAA systems.

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interactions between bottom-feeding fish (common carp, Cyprinus carpio L., and hybrid tiiapia) and a filter feeder (silver carp, Hypophihalmichihys motitrix (Valenciennes)) in polyculture were studied in fertilized ponds with no supplementary feeding. The silver carp were stocked at two densities: 1300 and 2600/ha. Growth rate and yield of each of the species were also compared with those in polycuhure of bottom feeders alone, and in a monoculture of silver carp alone, at the same densities. The consumption of natural feed as melabolizable energy (ME) was calculated by the energy balance (requirement for maintenance and growth divided by the utilization efficiency).Increasing the density of silver carp reduced proportionally their own growth rate, due to the limited amount of food. Above a density of about 1000/ha. silver carp inhibit the growth rate of common carp and tilapia. This inhibition was small at 1300 silver carp/ha, but considerable at 2600/ha. However, the presence of bottom feeders increased the growth rate of silver carp at both densities. Calculated natural food consumption showed that growth interactions between species were brought about through the availability of food. The synergistic effect of the bottom-feeding fish on the silver carp is assumed to be due to ihe upwelling of bottom nutrients to the upfjer layers of water by the burrowing of the fish in the mud. Combined yield of all species in the polyculture was highest at the density of 1300 silver carp/ha (2116 kg/ha in 156 days). At 2600 silver carp/ha the inhibition of growth rate of silver carp itself, reduced total yield as compared with the lower density.

The effects of four rates of application of fertilizer, with cow manure (3000 kg ha ±1 ), urea (100 (kg ha ±1 ) and triple super phosphate (TSP) (100 kg ha ±1 ) (treatment F)), treatment F Q 0.5 (treatment 0.5F), treatment F Q 1.5 (treatment 1.5F) and treatment F Q 2 (treatment 2F), on periphyton, plankton and water quality in tropical freshwater ponds were studied. The highest periphyton biomass in terms of dry matter (3.27 mg cm ±2 substrate), ash-free dry matter (2.06 mg cm ±2 substrate) and chlorophyll a (7.49 mg cm ±2 substrate) developed in treatment 1.5F. The ash content of periphyton was lower in treatment 1.5F (38% of dry matter) than in other treatments (57±66% of dry matter). Total ammonia and chlorophyll a of water increased with fertilization rate. Treatment 1.5F (cow manure, urea and TSP at rates of 4500, 150 and 150 kg ha ±1 respectively) appears to be the optimum, yielding high quantity and quality periphyton. By supplying a substrate area for periphyton equivalent to the pond surface, it was estimated that this level of fertilization could support a ®sh production of around 5000 kg ha ±1 y ±1 , without recourse to supplementary food.