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Two feeding experiments were carried out on #Pangasius hypophthalmus$ larvae reared in a recirculating water system during 8 days. The first experiment was done at the Can Tho University (Vietnam) and the second at the RIFF Sukamandi station (Indonesia). The main objective of the first experiment was to compare survival and growth peformance of #P. hypophthalmus$ larvae fed with either #Moina$ sp. or #Artemia$ nauplii and with either strong or moderate aeration. Strong aeration was tested in order to homogenise prey repartition in the water column, since #Artemia$ and #Moina$ sp. tended normally to be concentrated in corners or at the bottom of the tanks. Two feeding rates (150 and 4000% of fish biomass) were tested. The second experiment aimed at an evaluation of optimal feeding level with #Artemia$ nauplii, by considering growth, number of ingested preys and survival rates of larvae. Each of three feeding levels (R1, R2 and R3) were tesed at three different fish stocking densities (10, 30 and 90 larvae/L). The feeding level R1 was adjusted daily according to a pre-established model of the number of #Artemia$ ingested as a function of age in #P. hypophthalmus$ larvae. The rations R2 and R3 were respectively 3 and 9 times greater than R1. The prey asscessibility (number of prey per litre), which varied as a function of the different combinations of feeding level x fixh stocking density, was also considered as a parameter that could influence larval growth and survival. The results of the first experiment indicated that both #Artemia$ and #Moina$ sp. could be used as a first feed for #P. hypophthalmus$ larvae. However, larvae fed #Artemia$ nauplii presented a faster growth rate than those fed #Moina$. Perturbation of the rearing media by strong water aeration resulted systematically in reduced larval survival rates, whatever the type of prey and feeding rate used... (D'après résumé d'auteur)

Over a 2-year period at the Sukamandi station (West Java, Indonesia), 87 #P. hypophthalmus$ females selected on the basis of a modal oocyte diameter greater than 1.0 mm were treated with Ovaprim (n=77) or hCG (n=10) to induce oocyte maturation and ovulation. The two hormonal treatment led to similar results in terms of ovulation percentage (86 and 90%), hatching rates (69 plus or minus 28 and 82 plus or minus 11%) and relative fecundity (167,000 plus or minus 18,000 and 128,000 plus or minus 60,000 eggs/kg, with Ovaprim and hCG respectively. The latency period between the last hormone injection and ovulation was negatively correlated to water temperature but showed important variations at a same temperature depending on individual females (e.g. between 5-11 h at 28-29°C). The ovulation time was therefore difficult to predict accurately in this species. The assessment of survival time of ova maintained in ovario after ovulation showed that the process of ageing (overripening of ova) occurs rapidly in #P. hypophthalmus$. The overall quality of ova begun to decrease as early as 2 hours after ovulation and, after 3 hours, hatching rate dropped down and fraction of deformed larvae increased significantly in comparison to those observed at the moment of ovulation. In some individual females this evolution was even more rapid, with a sharp decrease in hatching rates between 1 and 2 hours post-ovulation. The duration of ova survival did not appear to depend on the type of hormonal treatment used (Ovaprim or hCG). For optimised gamete management in hatcheries, it is therefore recommended to check carefully the females for the occurrence of ovulation (between 3 to 11 h after the last hormone injection, depending on water temperature) and to collect and fertilise the eggs within less than two hours after this moment. (Résumé d'auteur)