Red Squirrelfish (Sargocentron rubrum) is a tropical fish present in all tropical seas and in particular in the Indian Ocean and the Pacific Ocean. This fish, as indeed for other tropical species, is now present in the Mediterranean sea, we owe it to the climatic warming of the sea, which creates favorable conditions, and to the Lessepsian migration: that is, to the entry and stabilization of animal and tropical species from the Channel of Suez.
Constructed in 1869 to provide a more direct trade route from Europe to India and the Far East, the canal is 162.5 km, with a depth of 10–15 m. and a width varying between 200 and 300 m. Because the surface of the Red Sea is slightly higher in elevation than the Eastern Mediterranean, the canal serves as a tidal strait by which Red Sea water pours into the Mediterranean.
The Bitter Lakes, which are natural hypersaline lakes that form part of the canal, blocked the migration of Red Sea species into the Mediterranean for many decades, but as the salinity of the lakes gradually equalized with that of the Red Sea, the barrier to migration was removed, and plants and animals from the Red Sea have begun to colonize the eastern Mediterranean.
The Red Sea, an extension of the Indian Ocean, is generally saltier and less nutrient-rich than the Mediterranean, an extension of the Atlantic Ocean, so Red Sea species, able to tolerate harsh environments, have advantages over Atlantic species in the conditions of the Eastern Mediterranean. Accordingly, most migrations between the two bodies of water are invasions of Red Sea species into the Mediterranean, and relatively few migrations occur in the opposite direction.
The construction of the Aswan High Dam across the Nile River in the 1960s reduced the inflow of fresh water and nutrient-rich silt from the Nile into the eastern Mediterranean, making conditions in the eastern Mediterranean even more like those of the Red Sea, thereby increasing the impact of the invasions.
This fish belonging to the Holocentridae family does not exceed 25 cm in length and has crepuscular and nocturnal habits. During the day it prefers to stay quiet and safe inside caves and ravines in the cliffs starting from the surface waters up to a maximum depth of 30 metres. Holocentridae is a family of ray-finned fish, the only family of the order Holocentriformes. The members of the subfamily Holocentrinae are typically known as squirrelfish. They are found in tropical parts of the Indian, Pacific and Atlantic Oceans, with the greatest species richness near reefs in the Indo-Pacific. Being largely or entirely nocturnal, they have relatively large eyes.
During the day, they typically remain hidden in crevices, caves, or under ledges. Red and silvery colours dominate. The preopercle spines (near the gill opening) of the members of the subfamily Holocentrinae are venomous, and can give painful wounds. The squirrelfishes mainly feed on small fishes and benthic invertebrates. The larvae are pelagic, unlike the adults, and can be found far out to sea. They are difficult to keep in the aquarium even though they are sought after for their beauty and colour.