Impact assessment of a large river on the sediments and fish from its continental shelf: using Solea solea as sentinel in the Ebro river mouth (NW Mediterranean, Spain)

Many studies have been carried out along mighty rivers with heavily industrialized watersheds to evaluate pollutants and their effects on freshwater organisms. However, their impact on marine organisms is virtually unknown. In order to cover this gap, Solea solea, one of the most important commercial fish species, together with sediments, were sampled during 2013–2015 offshore from the Ebro Delta river mouth. Fish health indicators (condition indices, histological tissue alterations, and parasite descriptors) were used to assess the potential effect of pollutants, an issue of particular interest in the area following the dredging activities taking place in the river upstream in 2013. No major histopathological alterations were detected, but perivascular inflammatory foci (PIF) were frequently observed, especially in 2014. The most prevalent and abundant parasites were acanthocephalans and digeneans within the digestive tract and copepods on the gills. Levels of trace metals from sediments and fish muscle were below the effects range median and reference levels accepted for human consumption, respectively. However, the lower levels of the hepatosomatic index, higher numbers of PIF, and variations in the abundance of parasites in 2014 and 2015 could suggest a pollutant exposure during these years. These results warn signs of toxicity, which could be associated with sediment leaks during the dredging activities.Versión del edito

A histological, histochemical and ultrastructural study of the digestive tract of Dentex dentex (Pisces, Sparidae)

Dentex dentex has a short esophagus, a large caecal type stomach, three to six pyloric caeca and a short intestine. Light and electron microscope studies reveal that the esophageal mucosa displays primary and secondary folds, a stratified squamous epithelium with fingerprint-like microridges alternating with a few zones formed by a single layer of columnar cells with apical microvilli. Only primary folds are present in the stomach, which is rich in simple tubular glands, these being absent in the pyloric valve. Two cell types occur in the gastric glands, one with a well developed apical intracytoplasmic membrane system consisting of a vesicular network of smooth membranes, and the other with a supranuclear tubulovesicular system. Pyloric caeca and anterior and posterior intestine mucosae display the same pattern of folding, with primary and secondary folds, without following a definite pattern in their orientation. In the rectum, the folds are oriented longitudinally. Small dense particles containing chylomicrons appear in groups in the intercellular spaces of the caecal and anterior intestinal epithelia. Eosinophilic granular cells (mast cells) appear along the digestive tract mainly within the stratum compactum. Histochemical studies reveal no differences in the composition of goblet cell mucus along the digestive tract. No histochemical differences were detected between enterocytes of the intestine, pyloric caeca and rectum. Neutral mucosubstances dominate in the stomach epithelium and in the goblet cells of the esophagus, pyloric caeca and anterior intestine. Results of the present study are discussed in relation to descriptions of the digestive tract in other sparids