Schooling fish are one of the more uncommon and hypnotizing sights to see on a dive. The way they move in perfect unison with no visibly perceptive cues that direct their movements is a biological characteristic that scientists have been studying for decades. A very common reason that fish school is as a defense tactic against predators through the use of the “oddity effect,” in which researchers hypothesize that fish of a certain species will shoal with others that look just like them in order to avoid standing out, which would make them more vulnerable to predators. One of the best examples of this tactic is seen in sardines, who form massive bait balls when threatened to thwart predators, turning and flitting in a frenzy to confuse the hungry beast who would have them for lunch.
But defense isn’t the only genius behind schooling, as we see with the Plotosus lineatus, more commonly known as the striped eel catfish. These extraordinary marine catfish are distinct in appearance, with the characteristic head of a catfish, bearing four pairs of barbels around the mouth, but the elongated, agile body of an eel. Striped eel catfish do have fins; however, the second dorsal, anal, and caudal fins are fused together, which gives the anterior portion of its body the striking resemblance to an eel. The pectoral and first dorsal fins are more fish-like than the others, but these are the danger zones: particularly with Plotosus lineatus, these fins conceal spines that deliver a highly toxic venom when touched, one that could be fatal even to humans. It is for that reason, like most creatures in the sea, that you would be much better off just observing this species rather than trying to shake its hand!
Not to worry — the striped eel catfish is a very interesting species to watch, and you’ll rarely ever see one alone. These marine catfish employ schooling as a foraging technique, in order to get the absolute most out of the grounds upon which they feed. They act basically as a giant rotary machine, taking turns with their snouts in the substrate to look for food and hanging up top to keep an eye out for predators or intruders. At times they will float up into the water column, making for an even more fantastic spectacle. Check out this video of the Plotosus lineatus in full march.
