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The survival of several fish species in captivity depends on their adaptation to the environmental conditions and the biological characteristics. The objective of the study was to evaluate the influence of different light intensity levels in growth, behavior and skin pigmentation in juvenile of Lophiosilurus alexandri. Fishes were exposed to the following luminosities: 0, 218, 278, and 459 lux. The experiment was conducted for 75 days, in a water recirculation system with controlled temperatures and aeration. Catfish juvenile were distributed in 35 L aquariums, at the density of 0.28 ind L-1. In order to evaluate fish growth, weight, standard- total length, weight gain, food consumption, food conversion, biomass, specific growth rate and survival were measured twice times a month. Also, swimming behavior, skin pigmentation and plasma cortisol levels were evaluated. Light influences L. alexandri feed consumption, food conversion, behavior and plasma cortisol levels. Environments with low light are recommended for the L. alexandri growth.

The objective of the study was to verify the combination of live and frozen Artemia nauplii, in different salinized water, and its influence in growth and survival of the catfish Lophiosilurus alexandri (Steindachner, 1876) larvae. Larvae were exposed to a combination of two feeds and two different salinities: live Artemia nauplii + 0‰ salinity in the water; live Artemia nauplii + 2‰ salinity in the water; frozen Artemia nauplii + 0‰ salinity in the water; and frozen Artemia nauplii + 2‰ salinity in the water. The experiment was conducted in a randomized design, in a 2 × 2 factorial scheme, 5 replicates, during 15 days. The larvae final weight, weight gain, food conversion, standard and total length, biomass, survival, body width, intestinal quotient, Fulton’s condition factor, and water quality were evaluated. The use of Artemia nauplii and 2 ppm salinized water for L. alexandri larviculture proved to be adequate providing greater growth. This was due to Artemia nauplii being kept alive and attractive for the cultivation of larvae in salinized water, even though salt was a stress factor. Already, the frozen Artemia nauplii was a viable food but should be used preferably in times of lack of live nauplii and without salinization of the water.

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 pacamã (Lophiosilurusalexandri), a species with a benthonic habit, and curimatá-pioa (Prochilodus costatus), which swims actively in the water column. Larvae of pacamã and curimatá-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 Fulton's condition factor for pacamã 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 pacamã. For the curimatá-pioa, survival and biomass were similar for the different colors. The weight and Fulton's condition factor were higher for the larvae cultivated in green and blue tanks. This result could be associated with the adaptation of curimatá-pioa larvae to active swimming in the water column, searching for prey.A interferência da cor do tanque na percepção visual da larva de peixe e no sucesso do seu cultivo depende da caraterística de cada espécie combinada com fatores ambientais. Neste estudo foi investigado o efeito de tanques de cores claras e escuras na larvicultura do pacamã Lophiosilurusalexandri, espécie de hábito bentônico, e, curimatá-pioa Prochilodus costatus, que nada ativamente na coluna da água. Larvas de pacamã e de curimatá-pioa foram cultivadas por 10 dias, em tanques contendo 5 L de água, a uma densidade de 15 larvas L-1, luminosidade de 141.7 ± 8.95 lux, alimentados com náuplios de Artemia. Quatro cores de tanques foram usadas: verde e azul claras, marrom e preta (com quatro repetições). Para as larvas de pacamã, a sobrevivência, biomassa e o fator de condição de Fulton foram similares entre os tanques de diferentes cores. Entretanto, as larvas nos tanques verdes apresentara um peso menor do que as cultivadas nos tanques de cor preta e marrom, assim como um menor comprimento total, que as larvas cultivadas em tanque marrom. Estes resultados provavelmente têm origem da associação da cor do tanque com o hábito bentônico do pacamã. Para o curimatá-pioa, a sobrevivência e a biomassa foram similares entre as cores. O peso e o fator de condição de Fulton foram maiores para as larvas cultivadas nos tanques de cor verde e azul, seguidas pelo marrom e preto. Este resultado pode estar associado a adaptação das larvas de curimatá-pioa a natação ativa na coluna da água à procura de presa.

Experiments in the cultivation or ecological with fish larvae, invariably use the length and weight with parameters. Therefore, this experiment was accomplished with larvae of Lophiosilurus alexandri pacama aiming at to determine some sources of mistakes sampling in the measurement of the size and of the weight of fish larvae. It was evaluated five possible sources of mistakes then. The first was the mistake in the measure of the lengths total and standard, due sharpness of two observers' measurement. The second the mistake in the measure of the lengths total and standard, due to the proportionate shrink for the fixative formomalin to 10%. The third party was the mistake due two forms of drying of the larvae in the obtaining of the biomass. The fourth experiment was on the influence of the size and of the grouping of the larvas in the obtaining of weights. Finally the last tested the alteration of the biomass due to the time of permanence of the larvae in the balance. The importance can be verified of to determine and to accomplish an sampling protocol for measurements of fish larvae. For they present size and weight reduced, a small variation in the condition of the mensure, it can alter the result significantly, because significant alterations were verified above for the tests referred.

The development of the digestive system in larvae of the Neotropical fish P. argenteus was analyzed histologically. On the 3rd day after hatching, the digestive system comprised oropharyngeal cavity, esophagus and simple undifferentiated tube. Since secreting cells, positive to Alcian Blue (AB), were found in the esophagus, digestive activity in the initial phase had occurred. On the 18 and 28th days after hatching, the esophagus was positive for AB and Periodic Acid Schiff (PAS) stain. The stomach was fully differentiated, with the cardiac, fundic and pyloric regions. Different regions of the epithelium were characterized by basic and acidic secreting cells (AB and PAS positive). On the 18 and 28th days after hatching, the intestine was long, coiled and divided into proximal, middle and distal segments with pyloric ceca. Secreting cells in different regions of the gut were either positive or negative for AB and PAS. Results showed that larvae of P. argenteus exhibited digestive activity on the third day after hatching, with fully differentiated stomach and intestines on the 18 and 28th days and their different regions featuring secreting cells.