Myxobolid parasites infecting the gills of the Iberian nase, Chondrostoma polylepis (Steindachner), in Galicia (NW Spain), with a description of Myxobolus gallaicus sp. nov.

Three species of myxobolid parasites were found infecting the gills of the Iberian nase, Chondrostoma polylepis , in the River Ulla (Galicia, NW Spain), Myxobolus leuciscini , M. impressus and M. gallaicus sp. nov., which is described herein. Myxobolus leuciscini locates in the intralamellar space and the plasmodium begins to develop in the endothelium of the capillaries of the secondary lamellae. Myxobolus impressus plasmodia are located in the interlamellar multilayered epithelium. Myxobolus gallaicus plasmodia are elongated and are located exclusively in the central venous sinus of the branchial filament, suggesting that they begin their development in branchial endothelial tissue. We also present data on spore size and morphology, plasmodium and pansporoblast characteristics and pathological effects of the three species in the host branchial tissues.     

Development of digestive system and swim bladder of larval nase (Chondrostoma nasus L.)

Digestive tract and swim bladder differentiation during nase (Chondrostoma nasus L.) larval development was evaluated using histological methods. The mouth, pharynx and oesophagus were impervious at the time of hatching. The straight tubular intestine consisted of undifferentiated cells and was situated over the yolk sac. The intestine, lined with a single layer of columnar epithelial cells, opened on 2 day posthatching (dph). First evidence of protein digestion and absorption by the enterocytes was observed on the sixth day, while lipid digestion and absorption began on the ninth day of larval development. Intestinal mucous cells developed and became active by the fourth day. The posterior chamber of the swim bladder inflated on the third day, while the anterior one filled 12 dph. Complete yolk sac resorption took place on the ninth day.     

Microhabitat use by three endemic Iberian cyprinids in Mediterranean rivers (Tagus River Basin, Spain)

Abstract  Microhabitat use by three endemic Iberian cyprinids, Barbus bocagei (Steindachner), Pseudochondrostoma polylepis (Steindachner) , and Squalius pyrenaicus (Günther) was studied in terms of depth, mean water column velocity, focal height, focal velocity, distance to shore and substrate. Data were obtained by snorkelling during spring and summer at nine sites of the Tagus River Basin, Spain. Habitat suitability criteria (HSC) were calculated, including fish position and focal velocity in the water column. Species comparison showed differences in depth and focal height (indicating a vertical segregation), and greater water velocities for Pseudochondrostoma . Size-class comparisons mainly showed differences in depth and focal height (correlated with fish size). The fish groups (3 species × 3 length classes) were assigned to microhabitat functional types. The results are essential for environmental flow assessments and allow 2- and 3-dimensional habitat simulations in Mediterranean rivers; they are also useful to define critical habitats for the conservation of native fish populations.