There are inventoried 18 fish species in the National Park of the Sierra de Guadarrama and in its Peripheral Zone of Protection. Overall, the Sierra de Guadarrama has some biogeographic peculiarities regarding its ichthyofauna. For some species, such as the “Bermejuela” (Achondrostoma arcasii) or the “Lamprehuela” (Cobitis calderoni), the Sierra de Guadarrama constitutes their southern limit of distribution. On the other hand, for several other species, such as the Iberian barbel (Barbus comizo), it marks their northern border. As in most of Spanish rivers, there have been several fish species introductions in these water streams. Among the ones that occurred in the limits of the protected space, the Pumpkinseed (Lepomis gibbosus), the Iberian gudgeon (Gobio lozanoi), the Common Carp (Cyprinus carpio) and the Goldfish (Carassius auratus), are particularly noticeable.
The Sierra de Guadarrama spills its waters on its Castilian-Leonese side only to the drainage basin of the Duero, while the Madrid area is part of the Tajo basin. The comparison between the fish community of the Duero basin (Segovia) and the Tajo basin (Madrid) reveals a noticeable difference, with a fish community less rich in the Segovian slope, although better preserved, since there are fewer introduced or exotic taxa.
In the medium-high and high sections of the Segovian area, the predominant species is the Common trout, often associated with the Iberian gudgeon. In somewhat slower but well preserved zones, we find the Bogue, the “Bordallo” (Squalius carolitertii) and occasionally the “Lamprehuela”. On the other hand, in Madrid slope the areas with the highest species wealth are the Manzanares, Guadarrama and Lozoya rivers upper courses. Specifically, among the three rivers having the highest species richness in the Sierra, the high section of Lozoya shows a high conservation value, being most important species the Common trout (Salmo trutta), the Common barbel (Barbus bocagei), the Bogue (Chondrostoma polylepis), the Bordallo (Squalius pyrenaicus), the Bermejuela (Achondrostoma arcasii), the Calandino (Iberocypris alburnoides) and the Lamprehuela (Cobitis calderoni).
Among the fish fauna living in the river network intersected by the protected area, three species are classified as extinction risk status at the Community of Madrid level (the “Calandino”, the “Lamprehuela” and the Iberian barbel). On the other hand, none of these species is included in the National Catalog. Among all 17 species present in the protected area, there is a high rate of endemicity in a relatively small area, with the presence of 9 Iberian endemism.
Down below you can find a brief description of the most significant fish in the high mountain environments of the National Park:
Common trout (Salmo trutta): average size fish; it rarely reaches 60 cm and 10 kg weight in Spain. The colour is variable, usually with the typical black and red ocellated spots, which are not present in the tail fin. The common trout is present in all the Sierra de Guadarrama sub-basins. It is the typical representative species of the middle and high zones of the Sierra, in fast and cold waters.
Its feeding is based mainly on benthic invertebrates, insects and molluscs. Adults can also eat fish and amphibians. One outstanding item is the exceptional common trout populations present in the National Park, having a noticeable genetic purity. Even so, the specie is threatened in Guadarrama by genetic introgression from the repopulation specimens, generally coming from Central Europe. This fact has resulted in a cooperation program with the Madrid Polytechnic University, to keep in its facilities a genetic native trout reservoir and produce in farm fish, as to be able to undertake fish reintroduction or improvement programs.
Its hybridization reproductive mechanism makes Calandino females produce ovules in which the paternal genome is eliminated, so these ovules are genetically identical to the mothers producing them. Later, these eggs form hybrid origin zygotes with spermatozoa from the Chub (Squalius pyrenaicus).
Lamprehuela (Cobitis calderoni): is a small benthic species endemic to the Iberian Peninsula, not exceeding 8 cm length. Tthe body is cylindrical and elongated with a thin caudal peduncle and an inner mouth. It inhabits in the rivers middle and middle sections of the rivers, where water runs clear and well oxygenated.
It is a sedentary species, benthic and crepuscular. It prefers shallow banks with gravel and rock bottoms. It feeds mainly on aquatic invertebrates at the bottom of rivers. It has been mentioned in the middle-high zones of all the sub-basins of the Sierra de Guadarrama. Its populations in the area seem fragmented and regressed by the channels alteration, contamination and introduction of exotic species.