César Graziani

Evaluation of microalgae diets for Litopenaeus vannamei larvae using a simple protocol

We evaluated native marine microalgae isolated from NortheasternVenezuela, as food for Litopenaeus vannamei larvae,compared to six microalgae commonly used in aquaculture. We evaluated themicroalgal ingestability calculating the biomass consumed by larvae, later weevaluated three monoalgal diets on protozoea stages of L.vannamei over 72 hr based on the larval biomass,RNA/DNAindex and the proportion of stage retarded larvae. The presence of everymicroalgae species in the protozoeas digestive tract indicated theirconsumption. Chaetoceros spp. showed high ingestabilityandTetraselmis spp. and Skeletonema sp.Ch1 showed low ingestability. The native microalgaeChaetoceros sp. A1 and Chaetocerossp.G1 were evaluated as monoalgal diets compared to Chaetocerosgracilis. Ch. gracilis demonstrated the bestresults when the evaluation was performed with the RNA/DNA index. However, thesurvival rate, larval biomass and percentage of stage retarded larvae fed withChaetoceros sp. G1 were not statistically different fromthose fed with Ch. gracilis. Taking into account thatnative microalgae produced higher biomass in shorter times when they werecultured in field conditions, the results suggest that native microalgae areadequate for large-scale culture conditions, thus reducing costs. Thedetermination of microalgal size and the larval consumption, dry and organiclarvae biomass and specially the RNA/DNA index, were valuable features of thisevaluation. The protocol developed in this study could be used to evaluatemicroalgae quality under different environmental conditions and productionregimes.

Hybridization between the freshwater prawns Macrobrachium rosenbergii (De Man) and M. carcinus (L.)

Abstract The production of hybrids between Macrobrachium rosenbergii and other Macrobrachium species has great economical importance for aquaculture, but also has serious environmental implications when M. rosenbergii is present as an exotic species. In this study, intra- and interspecific crosses between M. rosenbergii and M. carcinus were carried out through natural mating and artificial insemination. For the natural crosses, a fertile female was placed inside an aquarium with a mature male and the behavior of animals was monitored. For the artificial insemination assays, male spermatophores were collected by electroejaculation and placed inside the sperm receptacle of a fertile female. The temperature was maintained at 27±2 °C during the study. Firstly, 62 and 45 natural intraspecific crosses were carried out in M. rosenbergii and M. carcinus , with larvae obtained from 32.3% and 57.8% of the crosses, respectively. Thirty-seven natural interspecific reciprocal crosses were also attempted but no mating occurred. A total of 57 and 39 intraspecific crosses were carried out by artificial insemination in M. rosenbergii and M. carcinus , obtaining larva from 22.8% and 41.0% of the crosses, respectively. Finally, 46 interspecific reciprocal crosses were also carried out by artificial insemination. Hybrid zygotes were produced in all the crosses, but embryo development did not progress further than the gastrula stage. This indicates the existence of both behavioral and postzygotic reproductive isolation barriers. These barriers could prevent the hybridization of these species in the natural environment.