Maximiano Núñez

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.

Crecimiento y supervivencia de los mejillones Perna perna, Perna viridisy de un morfotipo indefinido bajo cultivo suspendido

Se evaluaron el crecimiento y la influencia de factores ambientales bajo condiciones de cultivo suspendido del mejillón Perna perna L., P. viridis L. y una variante o morfotipo indefinido, que comparte sustrato y características morfológicas y de color de ambas especies. El estudio fue conducido durante 10 meses en la localidad de Turpialito, Golfo de Cariaco, Venezuela. Las tres poblaciones experimentales, sembradas con una talla inicial homogénea (45–50 mm) presentaron un patrón de crecimiento similar; sin embargo, P. viridis mostró tasas de crecimiento significativamente menores a las de P. perna y del morfotipo, alcanzando al final del estudio 71.2, 77.0 y 77.8 mm de longitud dorso-ventral de la concha, respectivamente. Los análisis de correlatividad de los factores ambientales y el crecimiento no mostraron una modulación definida del crecimiento somático debido a factores ambientales; no obstante, la actividad reproductiva, especialmente cuando se inicia por primera vez, puede actuar como factor endógeno negativo. Aunque los resultados muestran similar respuesta fisiológica de los mejillones, se observó mayor similitud entre P. perna y el morfotipo y diferencias suficientes entre éstas y P. viridis, sugiriendo que las dos primeras pueden estar más relacionadas genéticamente. Sin embargo, existieron diferencias entre el morfotipo y P. perna, en cuanto a las características fenotípicas de la concha, supervivencia e índice gonadosomático, que pueden establecer diferencias genéticas definidas. La mayor producción gonádica en la variante sugiere su selección para el cultivo.

Diversity and community structure of soft-bottom benthic molluscs in the Araya Peninsula, Venezuela: a baseline for the assessment of environmental impacts

The north-eastern region of Venezuela includes some of the most productive marine ecosystems of the country, sustaining high abundances of fisheries resources. This feature, coupled with the high diversity of coastal ecosystems, increases the interest for the development of conservation policies to prevent and/or mitigate negative environmental impacts associated with human interventions at the area. However, previous malacological assessments made in the Araya Peninsula are mainly restricted to epibiotic molluscs associated with bivalve banks. In this vein, we performed three different surveys for soft-bottom molluscs in the intertidal (using a stainless steel corer), shallow subtidal (Eckman dredge) and subtidal ( Arca zebra dredge) areas of Araya Peninsula. We found 41 species including Bivalvia, Gastropoda, one Cephalopoda and one Scaphopoda, although according to sample-based rarefaction techniques there may be several more undetected species. Since there is an ongoing project aiming to construct a shipping terminal on Araya Peninsula that could adversely affect coastal marine biodiversity in the region, the knowledge about the molluscan assemblage in the area is a key requirement for designing conservation measures.

Chapter 28 Venezuela

Publisher Summary This chapter discusses the scallops in Venezuela. The Venezuelan coast, in the southwestern Caribbean Sea, is a tropical region that supports a high diversity of bivalve molluscs. Most of these scallops are small and only Nodipecten nodosus and Euvola ziczac are exploited by coastal populations for local consumption, and a drag fishery exploits Amusium papiraceum, Amusium Laurenti, and Argopecten nucleus. Euvola ziczac forms small beds on sandy bottoms in areas of upwelling. It is a functional hermaphrodite and is unusual among tropical bivalves because of its markedly seasonal reproduction. Populations of N. nodosus along the northeast coast of Venezuela show even lower generic variability than E. ziczac, as the frequency of polymorphic loci is 1.92% and mean heterozygosity is 0.0016. A. papyraceum forms the major scallop beds in Venezuela and is fished commercially. It is part of a multi-species bottom trawl fishery, which targets shrimps, bottom fish, and molluscs. The large size of the adductor muscle of Euvola ziczac and Nodipecten nodosus suggests that they should be good species for aquaculture and a number of studies have evaluated their growth and survival in suspended and bottom culture.