Brooders of Surub|¤ (Pseudoplatystoma fasciatum) were caught in the Ichillo River (Bolivian Amazon) and adapted to captivity conditions for 1 year in the facilities of the experimental aquaculture station of 'El Prado' (Santa Cruz de la Sierra) under natural temperature and photoperiod conditions. Induced reproduction was obtained by means of Ovaprim s (Syndel, Canada) injections and arti¢cial fertilization. Sperm and ova were obtained by gentle stripping of male and female brooders. Fertilized eggs were incubated in 60 L Zug jars. A mean hatching rate of 73.7 AE 19.0% was obtained after 24 h at 26.5 1C. For larval rearing, several protocols were tested with different settings of photoperiod, light intensity, food type and period of distribution, and stocking density. The best survival rates were obtained with Artemia nauplii feeding in total darkness. A high level of aggressiveness between larvae and precocious appearance of jumpers was observed, but these can be controlled with appropriate rearing conditions. Values (n 5 23) represent minimum, maximum, mean and standard deviation (SD).Aquaculture Research, 2008, 39, 764^776 Induced breeding of Pseudoplatystoma fasciatum J Nun ì ez et al.

Temperature effects vary throughout the ontogeny, but are proportionally more variable during the early life stages than in older fish. The larvae of a few species have been studied but contrasting trajectories were observed, thereby making it difficult to predict how temperature impacts on the growth, survival and size heterogeneity in a particular species. This study examined these interactions in young [0.9 mg–1 g wet mass (WM)] Pangasianodon hypophthalmus, one of the most extensively cultured tropical fish. Fish were raised at five temperatures from 23 to 33 °C in a recirculated water system, fed in excess with a high‐energy feed (Artemia then a formulated feed, >50% protein), and examined at 1‐day (first feeding days) or 4‐day intervals (older fish). The temperature that produced the fastest growth (T°opt) was 31 °C at the start of exogenous feeding (0.9 mg); it increased to 32.7 °C at 8 mg then decreased by 0.7 °C for each 10‐fold increase of WM. Size heterogeneity was lower and survival was higher (70–85% from 0.9 mg to 1 g) when the temperature was close to T°opt. Comparisons with other species suggest that the slope of the relationship between T°opt and fish size has a strong latitudinal component, and may also reflect the fish sensitivity to oxygen.

Two experiments were conducted to evaluate the effects of three water recirculating duration (daytime (07.00h to18.00h); nighttime (18.00h to 07.00h); and 24 hours control) and shading (30%, 60% and no shading control), respectively, on growth and sap's nitrate content of lettuce in a commercial aquaponic system integrated with red tilapia culture. First experiment showed that water recirculating time did not affect the lettuce growth, thus offering the possibility to increase aquaponics profitability by reducing the operational cost. The second experiment revealed that shading affected nitrate content in the sap of the leaf midribs, but it remained in range specified by EU regulations in all treatments. The highest lettuce growth was observed at the rate of 30% shading whereas 60% shading gave the lowest growth (P<0.05).

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