Gonads of Eleginops maclovinus (Cuv. & Val., 1830) from the Beagle Channel (Tierra del Fuego, Argentina) were sampled weekly throughout the year and histologically analysed. Gonads containing solely or mostly testicular tissue were predominant in each length class smaller than 40 cm (80 to 100%). Sex ratio was almost 1 : 1 in fishes ranging from 41 to 45cm. Females were dominant in specimens larger than 46 cm (80 to 100%). Four testicular types are described according to maturation degree and absence or presence of female cells, one intermediate gonadal type and one typical ovarian type. It is concluded that this species is a protandrous hermaphrodite.

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SUMMARY: Serious concerns exist that the thinning of stratospheric ozone and the resulting enhancement in the solar UVB radiation, may impair marine primary productivity. Also, UVB may alter food web dynamics and food availability for higher trophic levels in marine ecosystems inducing changes in phytoplankton species composition. The main goal of this study was to examine the responses of different species of marine phytoplankton to solar UVR. Specifically, we compared the UV sensitivity of a phytoplankton natural community isolated from the Beagle Channel (54°52'S, 68°18'W, Ushuaia, Argentina), as well as the response of two taxa which were isolated from that community (i.e., a pennate diatom, Navicula sp., and a phytoflagellate pertaining to the Class Cryptophyceae) to UV radiation. Exposure to UVB or UVA radiation treatments had no significant effects (p>0.05) on exponential growth rate in Navicula sp. However, when the phytoflagellate [Class Cryptophyceae] was exposed to UVB, the growth rate in the exponential phase was inhibited significantly (p<0.01) compared with the PAR control. Marked changes in the relative abundance of the main taxonomic groups were observed in the community cultures: the relative abundance of phytoflagellates was significantly lower after exposure to the UVB treatment than after exposure to the PAR treatment (p<0.05). However, the percentage of centric diatoms increased significantly (p<0.05) when they were exposed to UVB. The growth rate at the end of the exponential phase of growth of the community was inhibited significantly (p<0.01) when the algae were exposed to UVB and UVA.Key words: Ultraviolet radiation, inhibition, phytoflagellates, diatoms, growth rate RESUMEN: DATOS PRELIMINARES SOBRE LOS EFECTOS CRÓNICOS DE LA RADIACIÓN ULTRAVIOLETA EN LA DINÁMICA POBLACIO-NAL DE ESPECIES FITOPLANCTÓNICAS DEL CANAL DEL BEAGLE, ARGENTINA. -Existe una gran preocupación por los efectos que podría ocasionar un aumento de la radiación ultravioleta (en especial UVB, 280 -320 nm) por la disminución de la capa de ozono, sobre los ecosistemas acuáticos. Con el fin de estudiar la sensibilidad de algunas especies fitoplanctónicas del Canal del Beagle (54°52'S, 68°18'W, Ushuaia, Argentina) a la radiación solar natural, se utilizaron cultivos monoespecíficos de un fitoflagelado (Clase: Cryptophyceae) y una diatomea (Navicula sp.) para determinar efectos a largo plazo (días) en la fase exponencial de sus tasas de crecimiento. Considerando la importancia de la composición específica en relación a la diná-mica de la cadena alimentaria y la subsecuente reserva de alimento disponible para los niveles tróficos superiores en el ecosistema marino, también se incluyó la respuesta de la comunidad en su conjunto. No se observaron efectos significativos (p>0.05) en la tasa de crecimiento exponencial cuando Navicula sp. fue expuesta a UVB ó UVA (320-400 nm). Sin embargo, cuando los fitoflagelados [Clase Cryptophyceae] fueron expuestos a UVB, su tasa de crecimiento fue inhibida significativamente (p<0.01). Al expo...