César Lodeiros

Bacillary necrosis in hatcheries of Ostrea edulis in Spain

Abstract Two hatcheries of flat oyster (Ostrea edulis) located in the North-West of Spain, which were affected by massive larval mortalities during summer months, were monitored in order to look for the causative organism(s) and the source(s) of the pathogens. Qualitative and quantitative analyses of the bacterial flora, conducted in different parts of the hatcheries, revealed that the total bacterial count (TVC) and the presumptive vibrios (PVC) increased during the spring, following the rise of temperature, up to the start of the outbreaks. Very high TVC levels were found in the phytoplanktonic food of broodstock and larvae; these bacterial populations were composed mainly of Flavobacterium and Pseudomonas but no vibrios were detected. Whereas the number of vibrios in the incoming water was effectively reduced by filtration and U.V. light, Vibrio strains were detected as part of the normal flora in the broodstock and larval tanks favoured by the conditions of nutrients and temperature provided in the hatcheries. The fact that vibrios were present in the gonads of hatchery-conditioned broodstock but not in wild oysters seems to indicate that these opportunistic pathogens can invade and proliferate in the oyster tissues, and subsequently infect the larvae. The agents responsible for the vibriosis outbreaks in both hatcheries resembled Vibrio tubiashii which produces lethal exotoxins for larvae and the typical symptoms of bacillary necrosis. Chloramphenicol was the most effective drug for controlling the disease.

RELATION OF SEASONAL CHANGES IN THE MASS OF THE GONAD AND SOMATIC TISSUES OF THE ZEBRA ARK SHELL ARCA ZEBRA TO ENVIRONMENTAL FACTORS

Abstract Over the period from June 2002 to June 2003, we examined the relationship of seasonal changes in the mass of the gonad and somatic tissues to environmental factors for four size groups of the zebra ark shell Arca zebra at Chacopata, in northeastern Venezuela. The gonads of A. zebra began to increase in size when individuals attained 18–20 mm in shell length, but maximum gonad mass relative to somatic mass was only attained at 55–60 mm in length. Large individuals (>50 mm) showed a distinct annual reproductive cycle with a marked increase in gonad mass from July to late September 2002, coinciding with the increase in temperatures related to stratification of the water column. A decrease in gonad size occurred during October 2002 through January 2003 and coincided with a temperature decline related to renewed upwelling. The mass of somatic tissues was highest between late August to late December 2002, coinciding with the reproductive period and elevated temperatures. Other environmental factors showed little seasonal variation, although chlorophyll a concentration was lowest during the major period of increase in the gonad and somatic tissues (July to late September 2002), suggesting that the animals were not limited by the abundance of phytoplankton food. A. zebra seemed to be well adapted to the high loads of inorganic seston found in the Chacopata region.

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.

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.

Componentes bioquímicos de los tejidos de Perna perna y P. viridis (Lineo, 1758) (Bivalvia: Mytilidae), en relación al crecimiento en condiciones de cultivo suspendido

In the organisms, the variations of the biochemical composition of reproductive and somatic tissues in the growth permit to infer about its adaptative to env...

Scallop Aquaculture and Fisheries in Venezuela

Abstract This chapter discusses the biology, fishery and aquaculture of scallops in Venezuela. The Venezuelan coast, in the southwestern Caribbean Sea, is a tropical region that supports a high diversity of bivalve molluscs, including 10 species of scallops. Nodipecten nodosus and Euvola ziczac are exploited along the coast for local consumption but are not abundant enough to support a commercial fishery. Industrial trawling was used to exploit Amusium papyraceum , Amusium laurenti and to a lesser extent Argopecten nucleus , until 2009, when this type of fishing was banned. Amusium papyraceum forms large beds in Venezuela and landings reached almost 1900xa0t per year in 1989. The large size of the adductor muscle of Euvola ziczac and Nodipecten nodosus suggests that these species should be good candidates for aquaculture and a number of studies have evaluated their growth and survival in suspended and bottom culture. Argopecten nucleus is a medium-sized scallop, up to 50–55xa0mm in shell height, and is also a good species for aquaculture; however, few studies have been conducted to establish techniques for its culture. For E. ziczac and N. nodosus , the low numbers of juveniles in natural beds and the small number of spat recruiting on suspended structures indicate that commercial culture would require spat production in a hatchery, and techniques for their production have been developed. Sufficient spat of Argopecten nucleus can be obtained from suspended collectors to support small-scale production, but a hatchery would be needed to support production on a commercial level. Hatchery and aquaculture techniques developed for scallops in Venezuela would likely be applicable to other areas in the Caribbean Sea.