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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 aim of the present study was to perform comparative histological analyses of the ontogenetic development of two fish species endemic to the Sao Francisco River in Brazil: Prochilodus argenteus and Lophiosilurus alexandri. Histological analyses were performed every 24 h from the moment of hatching until 14 days post-hatching (dph) for the observation of larval development and until 39 dph for the observation of gonadal development. Whole larvae were fixed in Bouin's solution and the histological slides were stained with haematoxylin-eosin. Lophiosilurus alexandri larvae had a larger body size compared with P. argenteus larvae since hatching. Lophiosilurus alexandri larvae had mouth opening and pigmentation of the eyes upon hatching, whereas these events were observed at 1 dph in P. argenteus larvae. The visualisation and the inflation of the swim bladder occurred at 1 and 3 dph, respectively, in the P. argenteus, whereas these events occurred at 2 and 8 dph, respectively, in L. alexandri. Yolk granules were absorbed at 4 dph in P. argenteus and the 10 dph in L. alexandri. At 7 dph, the digestive tube was more differentiated in L. alexandri than P. argenteus and at 14 dph, the digestive system of both species had features of their eating habits: broad stomach and short intestine in L. alexandri, typical of carnivorous habits; stomach with a mechanical function and long intestine in P. argenteus, typical of detritivorous habits. The epithelial lining tissue, formed by a single layer of cells in the newly hatched larvae (0 dph), differentiated throughout the study, exhibiting scales in P. argenteus and numerous club cells in the middle epithelial region of L. alexandri at 39 dph. Undifferentiated gonads with somatic cells and primordial germ cells were observed at 39 dph, with caudal-cranial migration since 1 dph in both species. The anatomic changes during the ontogeny of P. argenteus and L. alexandri larvae are directly associated with the evolutionary history of each species, which explains their feeding habits, behaviour and distribution in the environment: Prochilodus argenteus is detritivorous and actively swims in the water column, whereas L. alexandri is carnivorous and inhabits bottom regions. At 39 dph neither species exhibited sexual differentiation.