Edson Vieira Sampaio

Zooplankton community composition and some limnological aspects of an oxbow lake of the Paraopeba River, São Francisco River Basin, Minas Gerais, Brazil

Lagoa Massacara (marginal ao Rio Paraopeba-MG, Bacia do Rio Sao Francisco) foi estudada do ponto de vista de alguns aspectos limnologicos durante dois periodos do ciclo hidrologico (cheia e seca). A transparencia da agua foi baixa e semelhante nos dois periodos. No periodo de cheia ocorreu estratificacao, perfil de oxigenio clinogrado com camadas inferiores anoxicas, pH ligeiramente acido, alta condutividade eletrica no fundo, com maiores concentracoes de CO2 inorgânico, de ions amonio e taxa de producao primaria que na epoca seca. No periodo de seca ocorreu desestratificacao, perfil de oxigenio clinogrado com camadas inferiores nao anoxicas, pH ligeiramente acido, condutividade eletrica constantes, com maiores concentracoes de nitrato que na epoca cheia. A composicao e abundância da comunidade zooplanctonica nao demonstrou grandes flutuacoes nas duas epocas estudadas. A maior densidade e riquesa de organismos foi detectada na pos-cheia. Copepodas e rotiferos detiveram a maior representatividade numerica em ambos os periodos, nao havendo contudo especies dominantes. Foram identificados um total de 17 taxa de rotiferos, 6 de cladoceros, 4 de copepodas, 4 de protozoarios, e 2 de macroinvertebrados. As especies mais abundantes encontradas na cheia foram: Thermocyclops minutus, Keratella cochleares, Keratella lenzi, e Trichocerca capucina, e na seca Thermocyclops minutus, e Conochilus unicornis.

Efeito do tamanho da presa e do acréscimo de ração na larvicultura de pacamã

The effect of prey size selection and feeding on pacama Lophiosilurus alexandri larvae culture (native specie of San Francisco basin classified as threatened of extinction) was evaluated. The larvae were cultivated in aquariums during 16 days and fed with natural zooplankton, screened in 650 and 1300 µm sieve, with and without ration. The offer of zooplankton of largest size provided a better development of the pacama larvae, demonstrating the need of alimentary particles larger for the growth potential of the species. The increase of the amount of ration did not affect the performance of the larvae, evidencing low or lack of capacity in digesting the offered ration. The ration fed reduced the pH and increased the electric conductivity, worsening water quality, which did not affect the performance of the larvae.

Reproductive traits of the yellow-mandi catfish Pime/odus maculatus Lacepede (Osteichthyes, Siluriformes) in captive breeding

Pimelodus maculatus Lacepede, 1803 is an important fish of the Sao Francisco river basin, where it is economically significant in both professional and sports fisheries. The fish, maintained in captivity, was subjected to hypophysation with crude caip pituitary extract. Approximately 70% of the females treated spawned viable eggs. The eggs were opaque, demersal, yellow and free. Egg stripping was performed at 213 hour-degrees (duration = 8.3 h) after the second dose injection, at water temperature of 25-26oC. Hatching occurred at 394 hour-degrees (duration = 16.3 h) after egg fertilization, at water temperature of 24-25oC. Egg fertilization rate was 64.8%. The relationship between absolute fecundity (AF), initial fertility (IF) and final fertility (FF) and body weight are expressed, respectively, by AF = - 331 + 181717 Wt (r2 = 0.62), IF = - 16839+ 158123 Wt (r2 = 0.65), and FF = -9874 + 100365 Wt (r2 = 0.63).

Induced spawning and reproductive variables of the catfish Lophiosilurus alexandri Steindachner, 1876 (Siluriformes: Pseudopimelodidae)

Lophiosilurus alexandri is an endemic fish from the Sao Francisco River basin, Brazil. The aim of this study was to induce L. alexandri to spawn and to obtain data on several reproductive variables for this species. For induced spawning, adults were submitted to Cyprinus carpio pituitary homogenate (CPH). Nine of the 12 females (75%) responded positively to the treatment. The stripping of oocytes was performed 8.4 h after the second dose of CPH with the water temperature maintained at 26oC. The number of stripped oocytes per gram of ova was 74 ± 5 oocytes g-1, and the mean oocyte diameter was 3.1 ± 0.2 and 3.6 ± 0.2 mm, before and after hydration, respectively. The oocytes were opaque, yellowish, demersal, highly adhesive, and covered by a gelatinous coat. The total fecundity was 4,534 ± 671 oocytes, and the fertilization rate was 59%. The initial and final fertilities were 2,631 ± 740 and 1,542 ± 416 embryos, respectively. Larval hatching occurred up to 56 h after fertilization, and the larvae had a total length of 8.4 ± 0.1 mm. This work provides important biological information for L. alexandri that can be used for management and conservation of this species.

Larviculture of two neotropical species with different distributions in the water column in light- and dark-colored tanks

The influence of tank color on the visual perception of fish larvae and the success of their cultivation depends on the characteristics of each species combined with environmental factors. In this study, we determined the effect of light and dark tank colors on the larviculture of pacama (Lophiosilurusalexandri), a species with a benthonic habit, and curimata-pioa (Prochilodus costatus), which swims actively in the water column. Larvae of pacama and curimata-pioa were cultivated for 10 days in 5-L tanks, at a density of 15 larvae L-1 and luminosity of 141.7 ± 8.95 lux, and fed Artemia nauplii. Four tank colors were used: green, light blue, brown, and black (with four replications). Survival, biomass and Fultons condition factor for pacama larvae were similar in the different colored tanks. However, the larvae in the green tanks showed lower weight than those cultivated in black and brown tanks, as well as shorter total length than that of larvae in the brown-colored tanks. These results are probably due to the association between tank color and benthonic habitat of the pacama. For the curimata-pioa, survival and biomass were similar for the different colors. The weight and Fultons condition factor were higher for the larvae cultivated in green and blue tanks. This result could be associated with the adaptation of curimata-pioa larvae to active swimming in the water column, searching for prey.

Commercial feed and frozen Artemia nauplii for curimatã-pacu larvae in first feeding

Objetivou-se avaliar o fornecimento de nauplios de Artemia congelada, racao comercial e coalimentacao com nauplios de Artemia congelada e racao comercial no desempenho produtivo e qualidade da agua na larvicultura de curimata-pacu Prochilodus argenteus. As larvas foram cultivadas durante 21 dias sob os seguintes tratamentos alimentares: 100F (100% racao comercial); 67F33A (67% de racao comercial e 33% de nauplios de Artemia congelada); 34F66A (34% de racao comercial e 66% de nauplios de Artemia congelada); e 100A (100% de nauplios de Artemia congelada). As larvas submetidas aos tratamentos alimentares nao diferiram no desempenho, sobrevivencia, peso, comprimentos total e padrao, fator de condicao de Fulton e taxa de crescimento especifico. O fornecimento de racao comercial aumentou as concentracoes de amonia, prejudicando a qualidade da agua, enquanto que o fornecimento de Artemia proporcionou baixas concentracoes de amonia, parcialmente devido a facil limpeza. Portanto, pode-se empregar nauplios de Artemia congelados na larvicultura do curimata-pacu.