The objective of this study was to analyze population structure (spatial distribution, seasonal distribution and distribution by length classes, sex ratio and length-weight relationship) and aspects of the reproductive biology of Loricariichthys melanocheilus. Fish were sampled bimonthly using gillnets and trammel nets in lentic and lotic environments in the rio Ibicuí, between the years 2000 and 2001. Were collected 410 specimens: 230 females, 164 males and 16 specimens whose sex could not be determined. A greater number of specimens were collected in October/November and December/January and in lentic environments. The greater length classes had a higher amount of females ( p < 0.05) and the sex ratio in all sampling periods was 1.38 females per male. Both males and females showed positive allometric growth (b = 3.299 and b =3.487, respectively). The highest values for gonadosomatic index (GSI) and gonadal condition factor (K) were observed from August/September and peaked in October/November, just like the highest frequencies of females at maturity stage C (mature), which is indicative that the breeding season occurs at this time.O objetivo deste trabalho foi analisar a estrutura populacional (distribuição espacial, sazonal e por classes de comprimento, proporção sexual e relação peso-comprimento) e aspectos da biologia reprodutiva de Loricariichthys melanocheilus. Os peixes foram amostrados bimestralmente com redes de espera e feiticeiras em ambientes lêntico e lóticos no rio Ibicuí, entre os anos de 2000 e 2001. Foram capturados 410 indivíduos: 230 fêmeas, 164 machos e 16 indivíduos que não foi possível determinar o sexo. Foi capturado um maior número de indivíduos em outubro/novembro e dezembro/janeiro e em ambientes lênticos. As classes de comprimento superiores apresentaram maior quantidade de fêmeas ( p < 0.05) e a proporção sexual em todos os períodos amostrados foi de 1,38 fêmeas para cada macho. Tanto os machos quanto as fêmeas apresentaram crescimento alométrico positivo (b = 3.299 and b =3.487, respectivamente). Os maiores valores do Índice Gonadossomático (IGS) e do fator de condição gonadal (K) foram observados a partir de agosto/setembro, com pico em outubro/novembro, assim com as maiores frequências de fêmeas em estádio de maturação C (maduro), indicando que o período reprodutivo se dá nesta época.

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The reintroduction of threatened fish species in areas where wild populations have been depleted due to anthropogenic impacts is an increasingly popular conservation tool and mitigation policy. Despite the importance of fish reintroduction for conservation purposes, little is known about its efficiency. Here, we assessed the viability of reintroduction of the endangered migratory fish, Brycon orbignyanus, in an area of the Upper Uruguay River basin where the species has not been reported for more than 30 years. We released 4000 yearling juveniles in the Pelotas River in 2014 and maintained 400 juveniles in captivity as a control population. After three years, a total of 13 individuals was recaptured, of which, 10 were considered sexually mature with first maturation being recorded in animals larger than 42 cm in total body length. The age–length comparison with a control population growth curve showed that recaptured fish were slightly bigger than those in captivity. Furthermore, important ecological attributes as schooling behavior and dispersal capacity were recorded for all recaptured individuals. Combined, our results suggest that the re-establishment of a self-sustained population of locally extinct species B. orbignyanus in the Pelotas River may be successful if sustained over time and supported by conservation policies.

The aim of this study was to determine the composition of gastrointestinal content and protease and lipase activities in summer and winter as well as to evaluate the relationship between digestive enzyme activity and centesimal composition of gastrointestinal content and feeding habits of two omnivorous species, Rhamdiaquelen (Quoy &amp; Gaimard, 1824) and Pimelodusmaculatus (LaCèpede, 1803), and of two detritivorous species, Loricariichthysanus (Valenciennes, 1835) and Hypostomuscommersoni (Valenciennes, 1836). The activities of pepsin, trypsin, chymotrypsin, and lipase, and the levels of proteins and lipids in the gastrointestinal tract, were evaluated. The enzyme activities were not related to the centesimal composition of gastrointestinal content or feeding habits. This finding could be associated with the variations of nutrient availability over time in the environment, as was observed in the centesimal composition of food ingested by the fish in summer and winter. The analyzed enzymes exhibited a constitutive character in these species; that is, the digestive enzymes are always available in the gastrointestinal tract to digest any food that the fish may find as an adaptation to better utilize the nutrients available in the environment in winter and summer.

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ABSTRACT. Aiming to characterize aspects of the trophic ecology of Loricariichthys melanocheilus in the Ibicuí river, bimonthly samples were taken in lotic and lentic ecosystems. Fish were caught and fixed in 10% formalin and dissected for stomach content analysis. Items were identified to the lowest taxonomic level possible. Stomach fullness (SF), repletion index (RI) and intestinal quotient (IQ) were estimated. Diet was assessed by the frequency of occurrence and the volumetric method, combined to obtain a Alimentary index. Feeding activity was analyzed with mean values of SF, RI and vacuity index (VI), which represents the percentage of empty stomachs. These parameters were compared seasonally, spatially, and according to the circadian rhythm. The main items in the trophic spectrum of L. melanocheilus were detritus, sediment, plant organic matter, nematodes, micro crustaceans (Copepoda, Cladocera) and insects (Diptera, Trichoptera, Ephemeroptera and Odonata). No environmental or seasonal variations were found for the consumed items. Feeding activity showed seasonal and environmental variations according to RI but did not significantly change according to SF. The IQ was 1.51, and showed seasonal variations, indicating changes in the diet. Keywords: feeding activity, feeding habits, intestinal quotient, stomach fullness, trophic spectrum. Ecologia trófica de Loricariichthys melanocheilusReis & Pereira, 2000 (Siluriformes: Loricariidae) no rio Ibicuí, sul do Brasil RESUMO. Com o objetivo de caracterizar aspectos da ecologia trófica de Loricariichthys melanocheilus no rio Ibicuí, amostras bimestrais foram realizadas em ecossistemas lóticos e lênticos. Os peixes foram capturados, fixados em solução formalina 10% e dissecados para a avaliação do conteúdo estomacal, sendo os itens identificados até a menor categoria taxonômica possível. Foram obtidos o grau de repleção (GR), índice de repleção (IR) e quociente intestinal (QI). A dieta foi avaliada por meio da frequência de ocorrência e pelo método volumétrico, sendo ambos combinados para se obter o índice alimentar (IAi). A atividade alimentar foi analisada a partir das médias de GR, IR e índice de vacuidade, representado pela porcentagem de estômagos vazios. Estes parâmetros foram comparados sazonalmente, ambientalmente e de acordo com o ritmo circadiano. Os principais itens presentes no espectro trófico de L. melanocheilus foram: detritos, sedimento, matéria orgânica vegetal, nematoides, microcrustáceos (Copepoda, Cladocera) e insetos (Diptera, Trichoptera, Ephemeroptera e Odonata). Não foram observadas variações ambientais ou sazonais nos itens consumidos. A atividade alimentar mostrou variações sazonais e ambientais de acordo com o IR e não variou significativamente conforme o GR. O QI obtido foi de 1,51, e mostrou variações sazonais, refletindo mudanças na dieta.Palavras-chave: atividade alimentar, habito alimentar, quociente intestinal, grau de repleção, espectro trófico.

Although Brycon orbignyanus has traditionally been extensively fished in the Paraná and Uruguay basins, anthropic events and fishing pressure have substantially diminished natural stocks. Restocking programmes have, nevertheless, aided efforts to restore the stocks of this fish in its former ranges. The objective of this study was