There are no particularly dangerous species alerts for the Adriatic Sea; none of the species are lethal and unpleasant encounters can be avoided by making a note of the dangerous species and taking care when diving.
Species inhabiting the Adriatic that require caution do not attack first; their aggressive behaviour is the result of feeling threatened. A good example are moray eels. Divers will encounter them peering from a crevice or hole and, as they present a safe haven, morays will not flee, but defend their own, very aggressively. Their bite is exceptionally painful and wounds take long to heal.
Moray eels possess other hidden venoms in their blood, which are poisonous if ingested; however, they are thermally unstable and can be neutralised at high temperatures, through baking or cooking. Conger eels also have venomous blood, but they are not dangerous unless provoked.
Other fish are poisonous on the outside; they have venomous spines and sacs of venom on their gill covers. The most common are various species of scorpionfish and sea scorpions, which are easy to identify. They usually rest peacefully on the seabed, trusting the venom found in their dorsal, pectoral and anal fins.
Star gazers, found in sand and silt, have venomous spines that protrude outwards above their dorsal fins. Being stung by them can be painful and cause discomfort, but this only lasts for a couple of hours.
One of the most poisonous fifish are weevers; the most venomous is the smallest member of the species, the starry weaver. Their spines are located on the first dorsal fin and gill covers.
Important to note is that their most frequent victims are inattentive fishermen; a dead fish is just as poisonous as the venom remains in its spines.
Although a rare sight, divers are cautioned to beware of giant devil rays and common stingrays, whose venom is considerably weaker, but whose large tail spines can cause significant damage. Note: a distant cousin is the electric ray, whose charged sting is more of an unexpected shock than anything else.
Aside from fish, close contact with other marine species can be just as uncomfortable, notably with jellyfish, most of which are not dangerous. The Pelagia noctiluca jellyfish appears periodically, and in large numbers, in the Adriatic resulting in a larger number of stings.
Jellyfish are cnidarians, one of the oldest marine families, which also includes other members whose stings can cause discomfort. One such example is the Cerianthus membranaceus sea anemone often found in the shallows.
Jellyfish are the most free-floating of the marine organisms; they are bad swimmers and rely on currents; sea anemones are sedentary organisms, attached to rocks or the seabed.
Other species with spines, such as sea urchins, and those without them, that only enrich underwater crags, sandy seabeds or the open sea, yet pose no threat unless touched or disturbed, are not worth mentioning here.