Zrmanja River that is located in the southern part of Croatia is home to rare species – Proteus anguinus or Human Fish. This rare species is located in the area named as Zrmanja in Lika in Croatia. At the beginning of the hill Postak where it stretches into uneven Velebit Karst with its 70 kms extended river stream you could easily find Proteus anguinus. The river penetrates in the Adriatic Sea for several years. The waterway has sparkling lucid water which is home to several olms. Proteus anguinus is mainly found in the south-western region of Croatia. At the same time, it is measured to be the exclusive species in its type Proteus and the lone European country having complete cavern dwelling chordate. It is sporadically named as “human fish” by local people owing to its covering colour, comparable to white people in Croatia. However, in Croatia it is usually called “covjecja ribica” in local language. It is considered as an actual troglobiont. Proteus anguinus is also referred as amphibic salamander that is present in the Dinaric Karst, the regions alongside the Mediterranean Sea including Trieste in Italy and all the way to Bosnia and Herzegovina. Human fishes can only be traced in this area; it is termed as prevalent species Croatia, Bosnia and Herzegovina and other neighbouring countries as well.
Extra emergences can also be traced in Harz in Germany; Moulis in France and even Grotte Oliero in Italy. Throughout several years, detailed investigation led to numerous samples being collected from Croatia, Bosnia, Italy, Germany and sent for advanced technical objectives. Olms is measured to be the longest survived amphibian in Bosnia and even Croatia. Taking note of data of more than 45 years from a 450-animal incarcerated procreation settlement at the CNRS, Moulis, France, and the forecasted highest existence is roughly a century, and the standard grown-up olm existence is approximately 70 years in Croatia and Bosnia. If the forecasted existence is precise, it is considered to be double that of the subsequent longest-survived species, the Japanese gigantic salamander Andrais Japonicus at around 56 years. Personal samples have been preserved under semi-innate environments in tangible containers for up to 75 years in Croatia. This endangered species as explained by European Union Habitats Directive is to be preserved naturally in the most thorough manner. The hunting and even selling of Proteus anguinus is strictly prohibited in Croatia, Bosnia and adjoining countries as well.
According to researchers in Bosnia, European olms arrives at sexual development at 16 years and gives 35-40 eggs every 12 years. The overall diet comprises creepy-crawly larvae, mainly Trichoptera, Plecoptera and even Diptera larva. It also feeds on molluscs and amphipods as well. However, in incarceration, insects are also voluntarily eaten by Human fishes in Croatia. The overall structure of Olm is wrapped by the covering with a skinny coating of external mucous, concealed by the farthest cell coating, named as stratum mucosum. Several larval features of amphibian covering formation are sustained in pigment-less and even coloured sub-species of Proteus anguinus. Nevertheless, decline of Olms in countries like Croatia, Bosnia, Italy and Slovenia is due to tremendous changes in natural environment.