Larval development of hoplias cf. Lacerdae (Pisces: Erythrinidae) and delayed initial feeding effects

Larval development of Hoplias cf. lacerdae was studied under laboratory conditions. After hatching, ontogenetic changes were recorded on food-deprived larvae in 12-hour intervals. Mouth opening occurred after 2.5 days and notochord terminated flexure in 6.5 days. Notochord length increased at a constant rate until complete yolk absorption (13,5 days). Larval dry weight and body height diminished gradually up to 21 days after hatching, when all starved larvae died. Every 12 hours after yolk absorption, groups of larvae (n=15), were separeted, and fed with Artemia nauplii for 10 days. The point-of-no-return (when 50% of larvae were unable to feed or to assimilate ingested food after delayed feeding), was not apparent in this species

Toxicidade aguda do nitrito em larvas do peixe-rei marinho Odontesthes argentinensis (Teleostei, Atherinopsidae) Acute toxicity of nitrite on larvae of the marine pejerrey Odontesthes argentinensis (Teleostei, Atherinopsidae)

Este trabalho visou a determinar o efeito tóxico do nitrito sobre larvas do peixe-rei marinho Odontesthes argentinensis através de testes agudos com 96h de duração. As larvas utilizadas neste experimento foram cultivadas no Laboratório de Maricultura da FURG (Rio Grande - RS). Foi utilizada água do mar filtrada na salinidade 35‰, na temperatura de 23&deg;C, com fotoperíodo de 14 horas de luz e aeração constante. Diariamente, as larvas mortas foram retiradas e, em seguida, 100% do meio experimental foi renovado. Não foi fornecido alimento durante a exposição ao nitrito. As larvas foram expostas a cinco concentrações de nitrito: 50, 150, 250, 350 e 450mg L-1 N-NO2-, mais um controle onde o nitrito não foi adicionado. A CL50-96h (concentração letal para 50% dos organismos após 96 horas) e seu intervalo de confiança (95%) foram de 199,3 (142,0-279,6)mg L-1 N-NO2-. Os resultados deste trabalho sugerem que, assim como outras espécies de peixes marinhos, o O. argentinensis é uma espécie tolerante a altas concentrações de nitrito e é pouco provável que este último seja um problema para o cultivo intensivo desta espécie.<br>This work evaluated the toxicity of nitrite on larvae of the marine pejerrey Odontesthes argentinensis through acute exposure during 96h. Larvae used in this experiment were cultivated in the Laboratory of Mariculture of the University of Rio Grande. During the tests temperature was 23&deg;C, salinity 35‰, and 14 hours of light were provided. Every day dead larvae were removed and the experimental media were completely renewed. Larvae were deprived of food during the test. Concentrations for the acute tests were 50, 150, 250, 350 and 450mg L-1 N-NO2-, plus a control with no nitrite added. Lethal concentration for 50% of the organisms (LC50-96h), and its confidence interval, was 199.3 (142.0-279.6)mg L-1 N-NO2-. The results of the acute tests suggest that, as other species of marine fish larvae, O. argentinensis is tolerant to high concentrations of nitrite, and it is unlikely that it would be a problem for the intensive culture of this species

A study of the life history of brazilian sardine, Sardinella brasiliensis: II. spawning in 1970 and 1971

Distribution and abundance of eggs of Sardinella brasiliensis (=S. aurita), are presented for the years 1970 and 1971 and compared with that of the previous year (1969). The spawning size of three spawning seasons was calculated using Tanaka's method. Incubation time of sardine eggs was estimated using the method of Ahlstrom. During three spawning seasons a considerable change in the relative spawning size was observed. The spawning season (during spring and summer in the southern hemisphere) of 1970-71 was poor when compared with those of 1969-70 and 1971-72. A slight change in the average diameter of eggs in different spawning seasons was also observed. The relation between oceanographie conditions and spawning size was analysed. It is suggested that the warm water covering the spawning ground during the 1970-71 spawning season may have caused an unsuccessful spawning in this year.<br>O presente trabalho apresenta a distribuição e abundância de ovos de sardinha verdadeira, Sardinella brasiliensis (=S. aurita), na costa sul do Brasil nos anos de 1970 e 1971. Um dos principais objetivos do estudo quantitativo de ovos e larvas de peixes é estimar o tamanho do estoque, através da abundância de ovos desovados. Com essa finalidade, a computação da abundância de ovos de sardinha verdadeira foi feita usando o método apresentado por Tanaka (1955). O tempo de incubação dos ovos de sardinha foi estimado com base no método da Ahlstrom (1943). A quantidade de ovos desovados variou durante os tres anos (1969 a 1971). Foi feita uma comparação entre a abundância total de ovos desovados e a freqüência de ocorrência de ovos nas estações da região estudada. Os índices de abundância mostram que a desova na época de 1970-71 foi muito fraca, comparada com as de 1969-70 e de 1971-72. Para esclarecer a relação entre a variação anual de tamanho da desova e a condição ambiental, foi analisada a temperatura e salinidade da água na area de desova. Os resultados indicam que, por ocasião da desova realizada em 1970-71, a temperatura da água era maior do que a dos outros dois anos. Esta água quente que cobriu o centro da área de desova (na faixa de 51 a 100 m de isóbata), foi considerado o motivo fundamental do fracasso da desova nesta época. O diâmetro dos ovos de sardinha foi comparado com os de outros anos. A media de diâmetro dos ovos desovados em 1971-72, foi um pouco maior do que a das outras épocas

Tolerância de juvenis do pampo Trachinotus marginatus (Teleostei, Carangidae) ao choque agudo de salinidade em laboratório Acute salinity tolerance of juvenile pompano Trachinotus marginatus (Teleostei, Carangidae) under laboratory conditions

O pampo Trachinotus marginatus é uma espécie com potencial para piscicultura, mas a sua utilização pode ser limitada pelas variações de salinidade comuns em estuários ou em ambientes super-salinos. Este trabalho foi realizado com o objetivo de determinar a tolerância à salinidade de juvenis de T. marginatus em laboratório. Foram testadas 12 salinidades em duplicata (0, 6, 8, 10, 15, 25, 45, 55, 58, 61, 65 e 75‰) e um tratamento controle (35‰). Dez peixes (comprimento total: 20,7&plusmn;2,3mm e peso úmido: 427&plusmn;113mg) foram colocados em tanques plásticos de 3L. A temperatura da água foi mantida em 24&ordm;C com um banho termostatisado, aeração constante e, a cada 24 horas, os meios experimentais foram completamente renovados. Após 96 horas de exposição, as salinidades letais médias inferior e superior, com os respectivos intervalos de confiança (IC 95%), foram estimadas em 6,99‰ (IC 95% = 6,86-7,13‰) e 58,50‰ (IC 95% = 56,81-60,24‰), respectivamente. Estes resultados permitem caracterizar esta espécie como eurialina. O estudo da influência da salinidade sobre T. marginatus deve ser aprofundado, buscando avaliar principalmente os efeitos sobre o crescimento, de modo que seja possível determinar o potencial do seu cultivo em ambientes com diferentes salinidades.<br>The pompano Trachinotus marginatus shows good potential for aquaculture, but the success of its culture might be limited by the salinity fluctuations common in estuaries or in hyper-saline environments. The objective of this work was to establish the salinity tolerance of juvenile T. marginatus under laboratory conditions. Twelve salinities (0, 6, 8, 10, 15, 25, 45, 55, 58, 61, 65, and 75‰) plus a control (35‰) were tested in duplicate. Groups of ten fish (total length: 20.7&plusmn;2,3mm and wet weight: 427&plusmn;113mg) were placed in plastic tanks with 3L of water. A water bath was set to control the temperature at 24&ordm;C, water was continuously aerated, and completely exchanged every 24h. After 96 hours, lower and upper medium lethal salinities and their respective confidence intervals (CI 95%) were estimated as 6.99‰ (CI 95% = 6.86-7.13‰), and 58.50‰ (CI 95% = 56.81-60.24‰), respectively. These results allow the characterization of this species as euryhaline. The influence of salinity on T. marginatus should be studied with more detail, with special attention to its effects on growth, in order to determine the potential for T. marginatus culture in different salinities

Spawning areas, dispersion and microhabitats of fish larvae in the Anavilhanas Ecological Station, rio Negro, Amazonas State, Brazil

The abundance and distribution of ichthyoplankton and their relationships to current velocity, temperature, dissolved oxygen, pH and electrical conductivity of the water in the Anavilhanas Ecological Station, Negro River, Amazonas State, Brazil, were analyzed. Preferred microhabitats for spawning, dispersion and nursery were also verified. Sampling was undertaken during the falling water period of 2001 and the rising water period of 2002, in a section of 100 km subdivided into 5 subsections, with a total of 20 stations (5 beaches, 5 ravines, 5 channels, and 5 lake channels) at night and during the day at the surface and at the bottom. 647 eggs and 4,187 larvae were captured, belonging to 10 families and four orders: Characiformes (6), Siluriformes (2), Perciformes (1), and Clupeiformes (1). Engraulidae (55.39%), Pimelodidae (30.45%), Auchenipteridae (5.23%) and Sciaenidae (5.13%) were the dominant families. The hierarchical statistical model (ANOVA) with three factors (microhabitat, depth and period) was applied to the environmental variables and the larval abundance, showing greater abundances of sciaenids in the ravines and lower abundances of engraulids in the channels. The highest captures were obtained at lower temperature values, at the bottom during the day and at the surface at night, suggesting an active larval behavior. The presence of the four larval development stages in all subsection for pimelodids and sciaenids, and in three subsections for engraulids, indicates that the Anavilhanas Ecological Station is an important spawning and nursery area for species of these groups in the Negro River. Larvae abundance of all characiform families was extremely low (from 0.1 to 1.17%), suggesting that they do not spawn in this system