Comparative ecology of the European eel, Anguilla anguilla (L.1758), in a large Iberian river

A total of 1,816 eels were sampled in 1988, from seven sampling areas. Four areas were located in brackish water and the remaining three were located in freshwater reaches of the Tagus river basin. Eels were more abundant in the middle estuary and decreased both in the upstream and in the downstream directions, with a predominance of males in higher density areas. Smaller individuals preferred more peripheral areas, such as margins and upper reaches in the brackish water zone, and the tributaries of the freshwater habitats. It was assumed that this distribution pattern resulted from three main factors: (i) the dominance of larger specimens; (ii) the need to avoid predators and; (iii) the search for better trophic conditions. The condition of the individuals generally decreased toward the upper reaches, apparently due to a corresponding decrease in feeding intensity. The presence of the Belver dam in the main river, 158 km upstream from the sea, seemed to impose major alterations to the described patterns. The concentration of specimens below this impassable obstacle yielded a reduction in the proportion of females and a decrease in the condition and survival of the eels, contributing to a reduction in the spawning success of this population. Suggestions to diminish the effects of the dam, and to preserve the fishery are also presente

Effect of silver on phase separation and crystallization of niobium oxide containing glasses

Effect of silver introduction in sodium phosphate and sodium borophosphate glasses containing large amount of niobium oxide have been investigated using differential scanning calorimetry and XRD. Same sodium niobate phase in the Nb2O5–NaNbO3 based solid solution have been observed following two heat treatments designed for nucleation and growth of the crystalline phase. Silver introduction in the glass composition is clearly responsible for increasing the crystallization rate. Its effect after nucleation and crystallization treatments has been shown. Phase metastable separation is occurring during heat treatment with formation of a phosphate rich and niobium rich phase. Crystallization effect on optical transparency of glasses and on Raman scattering response have been investigated