Isabel Riveiro

Identification of subpopulations in pelagic marine fish species using amino acid composition

The spatial stock complexity of marine fish species requires that population structure is taken into account in fisheries management. The aim of this study was to determine whether the amino acid composition (AAC) of the adult fish allows the identification of subpopulations within the stock. During a cruise in November 2003 along the entire Mediterranean coast of Spain, individuals were collected of the following pelagic species: Sardina pilchardus, Sardinella aurita, Engraulis encrasicolus, Trachurus trachurus, Trachurus mediterraneus, Scomber scombrus and Scomber colias. Individuals of S. pilchardus and E. encrasicolus were also collected from the waters of the Strait of Sicily in 2002 and 2003. The AAC of the fish eyes was seen to be species specific, and therefore, the differences in AAC among species may be based on inherited characters. Moreover, a clear differentiation was seen between the Spanish and Sicilian populations of S. pilchardus and E. encrasicolus. Furthermore, in the Spanish waters of the Mediterranean Sea, discriminant analysis revealed a substantial separation between the northern and southern subpopulations of S. pilchardus, S. aurita and E. encrasicolus. Temporal variations in AAC within species in each area were lower than the spatial variations observed among areas for each species, probably reflecting the influence on the AAC of the contrasting environmental characteristics of each area. Our results indicate that the ACC of the eyes in adult fish is a good tool for discriminating among subpopulations in pelagic marine fish species.

Effect of bacterial epiflora on egg hatching of the Atlantic sardine (Sardina pilchardus)

The aim of this work was to study the influence of bacterial epiflora on egg hatching of the sardine (Sardina pilchardus) obtained from a natural environment (Ría de Vigo, Spain) during the spawning season of the sardine (from January to June). Total bacteria, viable bacteria or the presence of specific potential pathogens for eggs, such as Pseudoalteromonas piscicida and Tenacibaculum (Flexibacter) ovolyticus, did not affect the viability of sardine eggs. Additionally, no relationship was observed between the presence of Vibrio spp., pathogenic for fish larvae, and the egg hatching. This was probably because the amount of bacteria associated with the eggs were between 10(2) and 10(4) orders lower than those found so far on the eggs of different fish species in rearing systems. Therefore, epiphytic bacteria did not affect the wild sardine eggs and, hence, in the area studied, it is probably not an important factor affecting annual recruitment success of this pelagic fish species.