Size at first maturity of Adelomelon brasiliana near Mar del Plata, Argentina, was established analysing gonad tissue samples and the secondary sexual characters. Age was determined through growth marks. Gonad matures after development of secondary sexual characters.

Minimum shell length at sexual maturity is 107 mm in females and 102 mm in males. The shell length at which 50% of the animals are mature is 115.1 mm in females and 107.25 mm in males (approximatley 7 years of age). In males, penis matures before testis. All animals are mature beyond 125 mm in females and 115 mm in males, respectively (approximatley 8 years of age). The comparative late sexual maturation in this species makes the population quite sensitive to over-fishing.

Whitemouth croaker (Micropogonias furnieri) maturity stages distribution and its relation to environmental factors was evaluated from 166 stations sampled within the Río de la Plata estuary (36°S–56°W) during spring 1994–1999 and 2003. A canonical correspondence analysis was used to explain whitemouth croaker distribution and estimate its relation to environmental factors (depth, surface and bottom waters temperature and salinity, bottom salinity and temperature horizontal gradients and vertical stratification). Results indicate that bottom salinity horizontal gradient (BSHG) and depth have a major influence on M. furnieri maturity stages spatial distribution; bottom salinity and temperature play a significant although secondary role. Spent and resting adult stages were associated to low BSHG, high salinity and low temperature while immature, gravid (with hydrated oocytes) and running stages to low salinity and high temperature. Although immature, gravid and running stages were clearly linked to similar bottom salinity they were segregated, with gravid and running stages associated to a strong BSHG. The distinct preferences of the different spawning stages result in a segregated distribution pattern along the main axis of the Río de la Plata estuary. The area with low salinity and high horizontal bottom salinity gradient (habitat for gravid and running stages) was located at the river head. The horizontal retention mechanism associated to BSHG within the spawning habitat favours growth and survival of fish larvae and the subsequent transport to nursery habitats.

The stomach contents of 69 Mediterranean spearfish Tetrapturus belone collected in the Strait of Messina, central Mediterranean Sea were examined. Of the total specimens, caught by harpoon, only three stomachs were empty. Their diet consisted mainly of pelagic fish and cephalopods. The most important piscine prey belonged to the families of Belonidae, Clupeidae and Scomberesocidae. Cephalopods were mainly represented by Tremoctopus violaceus in terms of per cent weight and by Illex coindetii in terms of per cent frequency of occurrence. Tetrapturus belone is an active predator on epipelagic fast-moving prey and school-forming species. Its ecological role is similar to that of other large pelagic species which share the same environment.

Heterodontus portusjacksoni was obtained from the catches of commercial trawl, gillnet and longline fisheries operating in south-western Australian waters, in which this shark is an abundant bycatch species. Ninety per cent of the H. portusjacksoni caught by commercial trawling in a marine embayment were <400 mm in total length, whereas 99 and 100%, respectively, of the individuals taken by commercial gillnet and longline outside that embayment were >400 mm. Although the differences between the size compositions in the catches obtained by trawling vs both gillnetting and longlining, which were similar, are partly attributable to gear selectivity, they also reflect a use by juvenile H. portusjacksoni of protected nearshore waters as nursery areas and a tendency for larger juveniles and adults to occupy reef/rock habitats in a range of water depths. The fact that all but one of the numerous H. portusjacksoni >800 mm were females is reflected in the ratio of females to males differing significantly from parity in the gillnet and longline samples. Yolked oocytes usually take one year to develop to ovulatory size. Ovulation occurs in late winter to early summer and hatching takes place a year later when the embryo is 180–220 mm. The claspers of males commence rapid growth at a total length of ~450 mm, coincident with the onset of clasper calcification and gonadal maturation. The rate of clasper growth relative to total length reached a maximum at ~570 mm and then declined precipitously as the claspers approached full calcification. Based on gonadal criteria, the L50 at maturity for females (805 mm) was nearly 40% greater than that for males (593 mm). Values of the deviance information criterion and marked overlap in their 95% confidence intervals demonstrate that the L50 of 581 mm derived for males using full clasper calcification as the index of maturity was equally valid as the above L50 derived for males at maturity using gonadal criteria. The capture of substantial numbers of juveniles by trawling and of females <L50 at maturity by gillnetting and longlining may be having localized effects on the population structure of H. portusjacksoni in south-western Australian waters.

Taxonomic distinction to species level of deep water sharks is complex and often impossible to achieve during fisheries-related studies. The species of the genus Etmopterus are particularly difficult to identify, so they often appear without species assignation as Etmopetrus sp. or spp. in studies, even those focusing on elasmobranchs. During this work, the morphometric traits of two species of Etmopterus, E. spinax and E. pusillus were studied using 27 different morphological measurements, relatively easy to obtain even in the field. These measurements were processed with multivariate analysis in order to find out the most important ones likely to separate the two species. Sexual dimorphism was also assessed using the same techniques, and it was found that it does not occur in these species. The two Etmopterus species presented in this study share the same habitats in the overlapping ranges of distribution and are caught together on the outer shelves and slopes of the north-eastern Atlantic.

The diet of the monkfish Lophius gastrophysus is described based on the analysis of stomach contents, for the south-western Atlantic from samples landed in the fishing port of Niteroi, Rio de Janeiro state, Brazil, from April 2004 to March 2006. Feeding intensity, measured as the presence or absence of contents in stomachs, and differences in the items' composition were analysed by sex, size-class and season. High feeding intensity predominated for females >32 cm and for males <31 cm. There was no seasonal pattern in the occurrence of full or empty stomachs. The most important category in the diet was fish with 25 identified species. Dactylopterus volitans showed the highest alimentary index value, mainly because of the feeding of juvenile monkfish. The second most important category was Mollusca, represented mainly by squid. No relationships between predator- and prey-lengths and weights were observed; but there was a tendency to consume light and small prey independently of the size of the monkfish.