Rearing and maturation of Lophiosilurus alexandri (Steindachner, 1876) in controlled conditions: First reports and future perspective.

Lophiosilurus alexandri is a freshwater carnivorous fish for which there is fishing pressure in its natural environment, yet the species has potential for captive rearing. Information on growth and sexual development for the species is scarce, and age and size at first maturation have yet to be determined. A total of 400 fish, therefore, were reared from hatching to 968 days after hatching (DAH). Fish gonads were histologically analyzed throughout the rearing period, and growth, the hepatosomatic index and the gonadosomatic index were compared between males and females. Estradiol, testosterone and 17α-hydroxyprogesterone concentrations were quantified at 845 and 968 DAH to compare sexually mature males and females. Weight and length did not differ between males and females (P >  0.05). Males were sexually mature at 593 DAH, with body lengths of 29.88 ±â€¯1.76 cm and weights of 444.1 ±â€¯77.03 g, while females were sexually mature at 845 DAH, with lengths of 36.51 ±â€¯1.06 cm and body weights of 783.05 ±â€¯48.57 g. The results provided important information regarding the minimum capture size of L. alexandri for identifying the appropriate period to begin reproductive management of the species.

Early sexing techniques in Lophiosilurus alexandri (Steindachner, 1876), a freshwater carnivorous catfish.

This study aimed to evaluate sexing techniques for juvenile Lophiosilurus alexandri. With this aim, we evaluated three techniques: coelioscopy, performed with the use of video surgery equipment; coeliotomy, a surgical procedure for direct visualization of the gonads; and sex determination using a urethral probe to compare the genital papillae. For coelioscopy, the survival rate was 100% 30 days after the procedure, and the fish restarted eating 10 days after surgery. This technique resulted in a 100% correct identification of individuals identified as females, whereas for males, it was 66.6%. There was no significant difference between males and females for anesthesia induction and recovery times. However, the procedure took longer for males because of the difficulty in observing the gonads, which can be attributed to the large amount of visceral fat in males. Coeliotomy also resulted in a 100% survival rate 30 days after surgery, and the efficiency of this technique was 96.3% for males and 93.9% for females. The fish restarted eating between 10 and 14 days after surgery, and there were no significant differences between males and females for anesthesia induction and recovery times for the surgical procedure to visualize the gonads (P > 0.05). The urethral probe technique was less efficient with an accuracy rate of 67.8% and 81.8% for males and females, respectively. We conclude that coeliotomy was more efficient for sexing both sexes of juvenile L. alexandri.

Capture, adaptation and artificial control of reproduction of Lophiosilurus alexandri: A carnivorous freshwater species.

The present study describes the capture adaptation and reproduction of wild Lophiosilurus alexandri broodstock in laboratory conditions. There were two periods when capturing was performed in natural habitats. The animals were placed in four tanks of 5m(3) with water temperatures at 28°C with two tanks having sand bottoms. Thirty days after the temperature increased (during the winter) the first spawning occurred naturally, but only in tanks with sand on the bottom. During the breeding season, there were 24 spawning bouts with egg mass collections occurring as a result of the spawning bouts that occurred in the tanks. The hatching rates for eggs varied from 0% to 95%. The spawning bouts were mainly at night and on weekends. In the second reproductive period, the animals were sexed by cannulation and distributed in four tanks with all animals being maintained in tanks with sand on the bottom at 28°C. During this phase, there were 36 spawning bouts. Findings in the present study contribute to the understanding of the reproductive biology of this endangered species during captivity.

Effect of water temperature and prey concentrations on initial development of Lophiosilurus alexandri Steindachner, 1876 (Siluriformes: Pseudopimelodidae), a freshwater fish

The aim of this study was to investigate the effects of water temperature and prey concentrations (Artemia nauplii) on the initial development of Lophiosilurus alexandri larvae. The experiment was conducted using a 4 x 2 factorial design, with four water temperatures (23, 26, 29 and 32 °C), two different initial prey concentrations (P700 and P1,300) and three replicates. Feeding was increased during the fifteen-day experiment. At the end of the experiment, the survival and condition factor were affected only by prey concentrations, with elevated numbers of Artemia nauplii leading to higher averages of these variables. The total length (TL) and specific growth rate were separately influenced by temperature and prey concentration, without interaction between them, and weight showed an interaction with these factors. In general, an increase of temperature (23 to 32 °C) improved the growth and nitrogen gain in L alexandri larvae. For TL, the optimal temperatures estimated were 31.4 and 31.0 °C for P700 and P1,300, respectively. Similar mean body weight larvae and nitrogen gain were observed at 23 °C for both levels of prey concentrations. For other temperatures, the P1,300 level provided greater weight gain for L. alexandri. Therefore, it is suggested that temperatures between 29-32 °C combined with a higher level of prey concentration maximise the development and nitrogen gain in L. alexandri larvae. Moreover, this is the first result about nitrogen incorporation in neotropical fish larvae.

O objetivo deste estudo foi investigar os efeitos da temperatura da água e concentrações de presas (náuplios de Artemia) no desenvolvimento inicial de larvas de Lophiosilurus alexandri. O experimento foi conduzido em esquema fatorial 4 x 2, com quatro temperaturas da água (23, 26, 29 and 32 °C), duas concentrações de presas (P700 e P1.300) e três réplicas. A quantidade de alimento ofertado aumentou durante os 15 dias de experimento. Ao final do experimento a sobrevivência e o fator de condição foram afetados apenas pela concentração de presas, sendo que a maior concentração proporcionou médias superiores para as variáveis mencionadas. O comprimento total (CT) e a taxa de crescimento específico foram influenciados separadamente pelos fatores temperatura e concentração de presa, sem interação entre os fatores, e o peso individual das larvas apresentou interação entre os fatores estudados. Em geral, o aumento da temperatura (de 23 para 32 °C) promoveu o crescimento e o ganho em nitrogênio nas larvas de L alexandri. Para o CT, a temperatura ótima ficou em 31,4 e 31,0 °C para P700 e P1.300, respectivamente. Médias semelhantes do peso individual e ganho em nitrogênio foram observadas nos animais cultivados a 23 °C em ambos os níveis de concentração de presas. Nas demais temperaturas, o nível de P1.300 levou a um maior ganho em peso para as larvas de L. alexandri. Desta forma, conclui-se que o desenvolvimento inicial das larvas de L. alexandri é afetado por ambos os fatores estudados, e temperaturas entre 29-32 °C combinados ao maior nível de concentração de presas são as melhores opções para maximizar o desenvolvimento das larvas e o ganho em nitrogênio. Em adição, esse é o primeiro resultado sobre a incorporação de nitrogênio em larvas de peixes neotropicais.