The fish in the lakes and rivers
There is not a great variety of fish species in the rivers and lakes in the Park and the natural population has been modified over the years by frequent stocking with hatchery trout. In recent years, however, the Park has approved the ecological Waters Plan, which contains specific indications on fish management, information that aims to improve the status quo, both through protection of the few remaining natural populations present and through stocking with local brown trout.
The fishing rights for the waters that run through the Park have been held by the municipal councils since the seventeenth century. The councils periodically hold public auctions to rent out stretches of the rivers. This has been common practice for the last fifty years, and is an important part of the councils' budget, however it has led to a gradual regression in quality of the fish population because of continual stocking with hatchery fish which are popular with those fishing, but of little value in waters that could host an ecologically well structured population.
Ittiofauna (4 foto)
Brown trout (Salmo t. trutta) are common in most Italian rivers, they come from North-European stock, which was domesticated and bred. Stocking the Park's rivers with hatchery trout has caused the loss of or genetic changes in most of the autochthonous brown trout (Salmo trutta macrostigma) and marble trout (Salmo marmoratus). These trout come from Mediterranean stock, originating from Southern Europe and North Africa and are perfectly suited to the Alpine environment. They were once common on the whole of the Tirrenean side of Italy, Sicily and Sardinia, nowadays they are reduced to a few residual areas. In Valle Gesso, Salmo trutta macrostigma, known locally as "the queen's trout" would seem to be extinct, unfortunately. Marble trout occupy an area lower in the valley compared to brown trout, in the Park territory their distribution has been upset and they are rarely found in a pure form, because they can hybridise with brown trout.
The area populated by bullheads (Cottus gobio) has also shrunk because of the huge numbers of salmonids that have been released rather than because of a worsening of the water quality, which is still very good in the Park. Bullheads have broad heads, and long well- developed ventral, dorsal and pectoral fins, they need cool, clear, well oxygenated water with medium to strong currents and a river bed of stones and pebbles. This species lives on the bottom mostly; in the daytime they hide under stones or among the vegetation, they become more lively at dusk as they are more active at night. They are territorial so the individual fish keep a distance between themselves. They eat benthic invertebrates or eggs and larvae of other species. Occasionally they cannibalise members of their own species.
Found here and there and certainly an introduced species, the rainbow trout (Oncorhyncus mykiss) is of American origin. Minnows (Phoxinus phoxinus), a European species, were introduced in a few lakes as bait for trout.