Grouper

Almost everything about grouper biology makes them slow to replace. They grow slowly and take years, sometimes a decade, to reach breeding age. They live a long time and reproduce over many years, so a population depends on the accumulated output of large old fish. Most are hermaphrodites that start as females and become males only when large, so removing the biggest fish can leave a population with too few males. They gather to spawn at predictable places and times, which fishers learn and exploit, sometimes taking most of a region's breeders in a short window. And they are highly valued food fish, so there is strong economic pressure to keep catching them. Together these traits have made groupers the most threatened group of large reef fish.

Not really. Large groupers, particularly goliath and giant groupers, are bold and curious and will approach divers closely, follow them, and sometimes deliver a startling thump by rushing in and opening the mouth, apparently expecting a handout or investigating. A very large individual could in theory injure a person, and there are anecdotal reports of near-swallowings and a small number of bites, mostly linked to spearfishing or hand-feeding. In practice attacks on divers are essentially unrecorded, and a big grouper hanging around a dive site is treated as a highlight rather than a hazard, though feeding them is discouraged because it changes their behaviour.

A grouper that has chased prey into a crevice it cannot enter will swim to a resting moray eel and perform a rapid side-to-side head shake right in front of it, sometimes then swimming to and pointing its body at the hole where the prey is hiding. The eel, which can thread into narrow spaces, often responds by going to hunt there. Either the eel catches the prey, or it flushes the prey back into open water where the grouper takes it, so both can benefit over many such episodes even though they do not share a single catch. It is one of very few documented examples of one species deliberately recruiting another to hunt.

They are close relatives in the same family, Serranidae, with the groupers usually placed in the subfamily Epinephelinae. In general, the fish called groupers are the larger, heavier-bodied, reef- and rock-dwelling ambush predators, while sea bass is used for a range of smaller and more streamlined members of the family, and also, confusingly, for various unrelated fish in other families. Size is the main practical divide. A fish over a few kilograms with a big mouth, lurking in a reef hole, is almost always called a grouper, while smaller relatives with the same shape are more often sea basses, hinds, or coneys.