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Neon tetras (Paracheirodon spp.) are three colorful characid species with a complicated taxonomic history, and relationships among the species are poorly known. Molecular data resolved the relationships among the three neon tetras, and strongly supported monophyly of the genus and its sister taxon relationship to Brittanichthys. Additionally, the sister-taxon relationship of the rummy-nose tetras Hemigrammus bleheri and Petitella georgiae was strongly supported by molecular and morphological data. Therefore, we propose to transfer the rummy-nose tetras H. bleheri and H. rhodostomus to the genus Petitella. Furthermore, Petitella georgiae is likely to be a species complex comprised of at least two species. [ABSTRACT FROM AUTHOR]

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AIM: Life-history strategies in fish include essential parameters related to offspring survivorship, fecundity and time of reproduction, which represent adaptive traits that enable a species to deal with spatial and temporal variability of abiotic conditions. This study aimed to compare reproductive traits associated to life-history theory for three Hyphessobrycon species from two lentic environments (four natural oxbow lakes and a man-made reservoir) of Mogi Guaçu River, upper Paraná River basin. METHODS: Specimens were collected with four minnow traps between August 2005 and July 2006 to cover dry and wet seasons (three samples in each season, and three samples in each environment). RESULTS: Reproductive strategy of H. bifasciatus and H. eques, which predominated in the oxbow lakes, differed from H. anisitsi in the reservoir. Hyphessobrycon bifasciatus and H. eques were single spawners with lower fecundity and size at sexual maturity, but invested more in number of eggs per body gram, while H. anisitsi was a multiple spawner species with higher fecundity, larger size at sexual maturity and body size. CONCLUSIONS: In seasonal environments, single spawners are synchronized with the floods to maximize juvenile survivorship, while reservoirs harbors multiple spawners’ fish due to the reduced fluctuation between high and low floods resulting from dam operation. Therefore, the seasonal condition in the oxbow lakes due to the flood pulse favored single spawners’ tactic, as showed by H. bifasciatus and H. eques. In contrast, the multiple spawning of H. anisitsi seems to be related to the more stable environmental condition throughout the year provided by the dam. Life-histories reported herein to Hyphessobrycon species must be common to other characid fishes inhabiting similar environments.

Background: ammonia (NH3) is the main excretion product from protein catabolism in fish, eliminated primarily through the gills. The proportion excreted by each species depends on factors such as protein quality, energy level and diet balance, body size of the animals, and environmental factors such as water temperature and pH. Objective: to determine the effect of dietary protein level (D1 = 250 g/kg, D2 = 300 g/kg, D3 = 350 g/kg) and body weight (P1 = 45 g, P2 = 250 g, P3 = 520 g) on ammonia excretion (AE) in white cachama (Piaractus brachypomus). Methods: basal AE level was determined by measuring water ammonia concentration every 2 h for 26 h after a 48 h fasting period. The AE in response to CP levels was determined for each fish size by measuring ammonia every 2 h for 26 h, after feeding them to satiety with the experimental diets. Results: basal AE was 177.2, 128.7, and 79.2 mg N-NH4+/day/kg live weight (LW) for P1, P2, and P3, respectively. The differences between treatments were significant (p<0.05). The AE rate, depending on protein level and body weight, was significantly different for all comparisons (p<0.05), similar to the comparison of main effects. Conclusion: the lightest fish and the highest protein content intake increased ammonium excretion. [ABSTRACT FROM AUTHOR]

RESUMO Avaliou-se o efeito dos níveis de metionina+cistina digestível para juvenis de tambaqui na fase inicial de desenvolvimento (3,03±0,06g) durante 45 dias. Foram utilizados 160 juvenis de tambaqui distribuídos em DIC, com cinco tratamentos (níveis de metionina+cistina digestível = 0,66; 0,73; 0,80; 0,87; 0,94%), quatro repetições e oito animais por unidade experimental. As dietas utilizadas foram isoproteicas (25%) e isoenergéticas (3200kcal.kg-1). Os resultados obtidos foram submetidos aos testes de homogeneidade, normalidade, à análise de variância e à análise de regressão. Os parâmetros físicos e químicos da água do sistema de recirculação ficaram dentro da faixa de tolerância para a espécie. Os níveis de metionina+cistina digestíveis avaliados não influenciaram (P>0,05) a sobrevivência, o índice hepatossomático, o índice de gordura visceral e o consumo de ração. Entretanto, ganho de peso e taxa de eficiência proteica apresentaram aumento linear (P