DIETA DE PEIXES EM ANTIGO RESERVATÓRIO HIDRELÉTRICO PARANAENSE

Introdução: As constantes pressões antrópicas de conversão de rios em reservatórios hidrelétricos tornaram-se crescentes nos últimos anos, resultando em mudanças nas características lóticas originais, e, consequentemente na abundância e riqueza da biota aquática. A reestruturação do ecossistema em termos de condições e recursos disponíveis direciona o sucesso das espécies na colonização do reservatório. Uma forma eficaz de compreender as mudanças ocorridas, principalmente aquelas relativas às relações tróficas é avaliar a dieta de peixes, visto que a maioria das espécies apresenta plasticidade trófica, atuando como bons amostradores dos recursos disponíveis no ambiente. Objetivos: Neste contexto, o foco deste trabalho foi a dieta de Tilapia rendalli e Deuterodon sp. A no reservatório hidrelétrico de Capivari, PR, Brasil. Material e métodos: As coletas foram realizadas trimestralmente, de março/1998 a agosto/1999 com a utilização de redes de espera com malhagens variadas, expostas por 24 horas, com despescas a cada oito horas. A análise dos estômagos foi realizada de acordo com o método de frequência volumétrica. Resultados: Foram analisados 10 estômagos de T. rendalli e 21 estômagos de Deuterodon sp. A. Tilapia rendalli apresentou hábito alimentar detritívoro, com dieta predominantemente composta por detrito sedimento (91,30%) e complementada com fragmentos de vegetais, microcrustáceoas e algas. Já Deuterodon sp. A foi onívoro, consumindo proporções aproximadamente equitativas de vegetais (30,86%) e microcrustáceos (39,16%) (especialmente Daphnia), além de insetos aquáticos, algas e detrito/sedimento. Conclusão: Os recursos consumidos pelas espécies foram condizentes com aqueles descritos na literatura. O reservatório hidrelétrico de Capivari é antigo (formado em 1970) indicando que as espécies presentes são aquelas com sucesso na manutenção de suas populações nas condições impostas por este represamento. Assim, o elevado consumo de detritos, vegetais e microcustáceos é um indicativo de que estes são recursos alimentares abundantes no ambiente. Aparentemente, vegetais e microcrustáceos desempenham um papel relevante como fonte alimentar para a ictiofauna, particularmente para Deuterodon sp. A, visto que esta é a espécie mais abundante deste reservatório.

Commercial-scale aquaculture of tilapia species in Zambia.

This case study describes the piloting and subsequent commercialization of an integrated pig and fish operation in Zambia. The initial scheme began in October 1981 using indigenous Zambian species including Oreochromis andersonii, Oreochromis macrochir and Tilapia rendalli. Different fertilization techniques were trialled, including organic (chicken manure) and inorganic (compound) fertilisers, and different integration systems were tested; ducks over fish and pigs over fish. Over the 29 years the project has been running, the variety of methods originally trialled have been refined to the extremely productive system in place today. Oreochromis niloticus is the dominant fish species produced, and members of the Clarias genus used as the main predator. The hatchery has been intensified (and now incorporates mono-sexing), aeration systems have been implemented in grow-out ponds and a green-water floating fish pellet has been developed. Yields have increased from an initial average of 2.5 to 3 tons/ha to present yields of over 11 tons/ha. The initial five hectare project has grown to over 45 ha of water producing over 600 tons of fish a year, and a stable herd of 200 sows producing in excess of 4100 slaughter stock per annum.

A case study of GK Aqua Farms in Chikwawa district, Malawi.

This study was carried out to record the experiences of Gopi Krishna (GK) Aqua Farms, with special reference to feeding/fertilization methods, the production cycle and the farm's marketing/distribution strategy. GK Aqua Farms is situated in Chikwawa District, which is in the southern region of Malawi. 19 ha (47 acres) of its land is under water, about 12 ha (30 acres) of which is in an enclosed, fenced area, and the remaining 7 ha (17 acres) in an open, unfenced area. Since GK Aqua Farms started practicing on a commercial scale in November 2004, the business has promoted aquaculture within Malawi and has demonstrated its potential profitability by attaining gross margins of over K3 million (approximately US $21,430) after just one year. The farm raises three species of fish in a polyculture system; common carp (Cyprinus carpio), Tilapia rendalli and Oreochromis siranus. The fish are sold in Chikwawa District as well as in the neighbouring city of Blantyre. The fish are fed artificial diets and are stocked in ponds that are mainly fertilized with livestock manure. Partial harvests are carried out throughout the year, depending on consumer demand, with a complete harvest once a year. The fish are sold at a farm gate price of K400/kg (US $3/kg) for common carp and K250/kg (US $1.8/kg) for tilapia species and at a wholesale price of K500 (US $3.6/kg) for common carp and K300 (US $2.1/kg) for both tilapia species. Since it took over the farm in 2004, GK Aqua Farms has had a continuous rise in production from 4.2 tonnes per year in 2004 to 29.5 tonnes per year in 2008 with an expectation of similar increases over the next few years. The farm faces several problems including pests, inefficient feed supply and low sales during summer. The farm, however, does not operate any integrated aquaculture-agriculture systems.

The effect of replacing fishmeal with kikuyu leaf meal on the activity of digestive enzymes and growth in Tilapia rendalli, Oreochromis mossambicus and Clarias gariepinus

The effect of replacing fishmeal with kikuyu on digestive enzyme activities was investigated in Tilapia rendalli, Oreochromis mossambicus and Clarias gariepinus. Five diets (30% CP: 20 MJ GE kg-1 DM) were formulated. In the control diet, fishmeal was replaced at 25, 50, 75 and 100% by kikuyu leaf meal. Each diet was assigned to three groups of 20 fish (per species). Fish were fed to apparent satiation three times daily for 60 days. There was a significant decrease (P less than 0.05) in protease, amylase and lipase activities at higher kikuyu inclusion. Protease activities were higher in T. rendalli followed by O. mossambicus and C. gariepinus had the lowest activities. The inability of the fish to produce enough enzymes at higher kikuyu inclusions resulted in significantly lower growth performance and poor protein digestibility. This decrease was more pronounced in C. gariepinus than the tilapias.

Microecology of Monogenean Gill Parasites of Tilapia Rendalli Boulenger, 1897 From Bamendjing Lake, Cameroon

The present work aimed to study preferences for microhabitat by the monogenean gill parasites of Tilapia rendalli Boulenger, 1897. Fifty-four specimens were sampled using gill net in February 2014 at Bamendjing Lake. Each gill arch was removed and examined to both quantify the number of parasites and their distribution on the gills. This examination enabled us to find 6583 specimens of monogeneans belonging to 5 different species, Cichlidogyrus arthracanthus, C. dossoui, C. quaestio, C. tiberianus and C. tilapiae with 3708, 1708, 858, 210 and 99 individuals respectively. All species were aggregated within the host population. The spatial distribution of each parasite species was studied on different partitions of the gill arches. This study supports the hypothesis that gill site preference is a result of water flow over gills during respiration and mate finding habitat. There was no evidence of competition among the various species.