The knowledge of embryonic and larvae development of fishes is a fundamental key which enables a closer approach to their biology and taxonomy. The present study aims to characterize piracanjuba (Brycon orbignyanus) embryonic and larvae development. During the whole embryogenesis, 15 to 20 embryos were sampled and analyzed. Eggs of B. orbignyanus are semidense, transparent, spherical, and bear a large perivitelline space. Hatching takes place 18 hours and 30 minutes after fertilization at 25 ± 0.8ºC. Total length and weight of just hatched larvae were 4.46 ± 0.39mm and 2.56 ± 0.73mg, respectively. Larvae presented entirely developed and pigmented eyes, as well as a vertical mouth opening of 15.2 ± 1.9% of body length, 36 hours after hatching, period from which intense cannibalism was observed.

The present study evaluated Nile tilapia when fed on dried duckweed in combination with commercial feed, aiming at reducing production costs. Three diets, which consisted of commercial feed (40% crude protein), dried duckweed or a combination of commercial feed and dried duckweed were fed to triplicate groups of 20 tilapia (Oreochromis niloticus) fi ngerlings. Fish weighing 3.2 ± 0.94g were stocked in nine 1-m 3 net cages and fed twice a day for 50 days. The fi nal average weights of fi ngerlings fed commercial feed (21.67g) and 50% feed + 50% dried duckweed (19.53g) were not different (p<0.05). Likewise, the specifi c growth rate did not differ between fi sh receiving these dietary treatments. Weight gain decreased as water temperature decreased along the experimental period, increasing feed conversion mainly for fi ngerlings fed on dried duckweed only. Also, when fed alone dried duckweed promoted the lowest weight gain and specifi c growth rate. It was confi rmed that dried duckweed can replace 50% (1:1 dry weight) tilapia fi ngerling 40% crude protein feed for a period of at least 50 days, without reducing growth. Key words: alternative dietary source, duckweed, lemna, tilapia ResumoDesempenho de alevinos de tilapia nilótica alimentados com uma combinação de lemnas secas e ração comercial. O presente estudo avaliou a utilização de ração comercial e lemna seca no cultivo de alevinos de tilápias nilóticas com o objetivo de reduzir os custos de produção. Três dietas representadas por lemna seca, ração comercial (40% proteína bruta) e uma combinação de lemna seca e ração comercial foram fornecidas a um grupo de 20 alevinos de tilápia (Oreochromis niloticus) em triplicata. Peixes com peso médio 3,2 ± 0,94 g foram estocados em nove tanques-rede com volume de 1-m 3 e alimentados duas vezes ao dia durante um período de 50 dias. O peso médio fi nal dos alevinos alimentados com ração comercial (21,67 g) e 50% ração + 50% lemna seca (19,53 g) não diferiram estatisticamente (p<0,05). Paralelamente, os peixes pertencentes aos mesmos tratamentos não apresentaram diferença signifi cativa no crescimento específi co. O ganho em peso foi menor em temperaturas mais baixas ao longo do período experimental, causando um aumento signifi cativo na conversão alimentar principalmente dos alevinos alimentados apenas com lemna seca. Além disso, a dieta composta apenas de lemna seca proporcionou o menor ganho em peso e taxa de crescimento específi co. Através dos resultados obtidos, conclui-se que a lemna seca pode substituir até 50% (matéria seca 1:1) da ração comercial (40% proteína bruta) utilizada na produção de alevinos de tilápia por um período de 50 dias, sem apresentar redução no crescimento. Unitermos: fontes alternativas de alimento, lemnáceas, tilápias nilóticas

No abstract

Despite successful introduction o f channel catfish into Brazil in 1980, no studies have been conducted to assess the performance o f channel catfish, Ictalurus punctatus, farming in southernBrazil. Fingerlings (27.Of 2.2 g) were stocked in sixteen 16-m2 tanks with cement walls and earthen bottoms. Four stocking densities were used: 0.5, 0.75, 1.0, and 1.25 fish/m2. Fish were fed a diet containing 32% protein according to a feeding chart for 257 days (from April to December). Water temperature ranged from 16.4OC to 30°C during the study. Final average weight (727.1 f 70.6 g) was significantly higher (P < 0.05) for fish raised at 0.5 fish/m2. Food conversion ratio (FCRJ was significantly higher (P < 0.05) for fish stocked at 1.25 fish/ m-.Survival averaged 95.4%, and no significant differences (P > 0.05) were found among treatments. There was no significant difference (P > 0.05) in tank production among the densities of 0.75, 1.0, and 1.25 fish/m2, but they were higher (P < 0.05) than the density of 0.5 fish/ m' . These results demonstrate the viability of channel catfish growth in southern Brazil. [Article copies available for a fee from The Haworllz Dociirnent Delivery Service: 1-800-342-9678. E-mail address: geti~~fojo@haworthpressinc.co~ll]