Moray eels are cosmopolitan eels of the family Muraenidae. The approximately 200 species in 15 genera are almost exclusively marine, but several species are regularly seen in brackish water and a few, for example the freshwater moray (Gymnothorax polyuranodon) can sometimes be found in freshwater. With a maximum length of 11.5 centimetres (4.5 in), the smallest moray is likely the Snyder's moray (Anarchias leucurus), while the longest species, the slender giant moray (Strophidon sathete) reaches up to 4 metres (13 ft). The largest in terms of total mass is the giant moray (Gymnothorax javanicus), which reaches almost 3 metres (9.8 ft) and can weigh over 36 kilograms (79 lb). The Morays have sometimes been described as vicious or ill-tempered. Morays hide from humans and would rather flee than fight. Morays are shy and secretive, and attack humans only in self-defense or mistaken identity (for example, a finger placed in a crevice where a moray resides may resemble a prey-item). Most attacks involve accidental bites during human-initiated interaction. Morays cannot see very well and rely mostly on their acute sense of smell. Morays, however, do inflict a nasty bite, and while the majority are not believed to be venomous, circumstantial evidence suggests that a few species may be. Eels that have eaten certain types of toxic algae or fish that have eaten some of these algae can cause ciguatera fish poisoning if eaten. Large morays can also cause extreme physical trauma, in some cases removing an incautious diver's finger. Morays rest in crevices during the day and hunt nocturnally, although they may ensnare small fish and crustaceans that pass near them during the day. Moray eels are cosmopolitan, found in both tropical and temperate seas, although the largest species richness is at reefs in warm oceans. Very few species occur outside the tropics or subtropics, and the ones that do only extend marginally beyond these regions. They live at depths of up to several hundred metres, where they spend most of their time concealed inside crevices and alcoves. While several species regularly are found in brackish water, very few species can be found in freshwater, for example the freshwater moray (Gymnothorax polyuranodon) and the pink-lipped moray eel (Echidna rhodochilus).
See How Big I've Gotten?
You can tell by Longfellow's bulbous head that he is becoming a mature Eel.