Vransko Lake belongs to Mediterranean zoogeographic area. Animals that live in the Park are very interesting, and from geological viewpoint, very old. In the Ice age, Vransko Lake was not covered with ice so very specific animal life had a chance to thrive here.
Except for very rich ornithofauna (bird species) that is described in the section ABOUT RESERVE, many other animal species can be found here.
Water in the lake is a bit salty, and considering that sea water penetrates the lake basin, both, freshwater and marine fish species are present in the lake. Of all the freshwater fish in the lake, only Eel (Anguilla anguilla) and River Blenny (Salaria fluviatilis) are autochthonous; which means that Vransko Lake is their natural habitat. Other species were introduced into the lake, either on purpose or accidentally. Some of them are Common Carp (Cyprinus carpio), that was introduced in 1949, Prussian Carp (Carassius gibelio), Common Rudd (Scardinius erythrophthalmus), Catfish (Silurus glanis), Pike (Esox lucius) and Eastern Mosquito Fish (Gambusia affinis) that was introduced because it feeds on mosquito larvae and thus controls their populations. Mullets are the most common marine fish in the lake.
Due to variety of moist and wetland habitats, Vransko Lake is a great place for amphibians. There are 8 species of amphibians present; 3 of them are on The Red List of Threatened Plants and Animals of Croatia and all 8 are threatened on the European level. Most amphibians are protected. Most common are Marsh Frog (Rana ridibunda), Common Tree Frog (Hyla arborea), Agile Frog (Rana dalmatina) and different toads (Bufo sp.). Salamanders (Salamandra salamandra), newts (Triturus vulgaris) and Yellow-Bellied Toad (Bombina variegata) are not so common.
Reptiles also benefit from the vast diversity of habitats at Vransko Lake. There are 20 reptile species present here. Some of the most common reptiles that can be found here are European Pond Turtle (Emys orbicularis), Hermann’s Tortoise (Testudo hermanni), European Legless Lizard or Scheltopusik (Ophisaurus apodus), Italian Wall Lizard (Podarcis sicula), Balkan Emerald Lizard (Lacerta trilineata), Common Wall Gecko (Tarentola mauritanica), snakes – Balkan Racer (Coluber gemonensis), Aesculapian Snake (Elaphe longissima), Grass Snake (Natrix natrix), Dice Snake (Natrix tesselata) and Nose-horned Viper (Vipera ammodytes). All reptiles besides Nose-horned Viper are under law protection.
Mammals found at Vransko Lake are typical for Dalmatian region. There are lots of mammals here and they play an important role in the food web. The most numerous mammals are rodents, insectivores, bats and carnivores, and there are about 40 different species present. Some of the most interesting species are: Eastern Hedgehog (Erinaceus concolor), Greater Horseshoe Bat (Rhinolophus ferrumequinum), Greater Mouse-eared Bat (Myotis myotis), Pipistrelle bat (Pipistrellus pipistrellus), Lesser white-toothed shrew (Crocidura suaveolens), European Polecat (Mustela putorius), Beech Marten (Martes foina), Wild Boar (Sus scrofa), Wood Mouse (Apodemus sylvaticus), Brown Rat (Rattus norvegicus) and Brown Hare (Lepus europaeus).
Finally, there are insects, the most numerous animal group. There is a large number of insect species at Vransko Lake, and some of most beautiful are surely butterflies and dragonflies. Through recent research on invertebrates, there are 133 spider species found, of which 15 species are recorded for the first time in Croatia.
The variety of habitats and animal species has a priceless value. Nevertheless, this whole system is very fragile and it is important to try to keep it as stabile and as natural as possible.