Which grouper are we talking about?
When we say grouper… which species are we referring to, actually?
A few things irritate us more than a pre-dive briefing where the divemaster says “we will spot some groupers”. ‘Coz grouper means all or nothing, and we do like to call what we see with a proper, exact name (if we know it!).
Dusky grouper (Epinephelus marginatus)
The dusky grouper (Epinephelus marginatus) is clearly the most iconic and most geographically widespread among the Mediterranean groupers. Who hasn’t seen, not even in a picture, its nice brown body with more or less numerous yellowish blotches, big fat African lips and curious eyes?
Some might envy the dusky grouper’s sexual life. Born as a female, the grouper in effect decides to become a… male at an age somewhere between 9 and 12 (60-70 cm length)! Such behavior, called protogynus hermaphrodite and after all relatively common in the fish world, is not so straightforward either: if the community is already overcrowded with males, the female grouper might indeed wait years before changing sex, therefore taking into account the social context.
Now, the reproduction is a true show for the few lucky ones who could observe it. The general opinion is that it takes a harem of 10 girl groupers for the maximum reproductive success of the boy one. In the heart of summer, with a new moon and for only a few minutes before or after sunset, the male starts rubbing itself on its females, one by one. Then, as soon as it feels inspired, together with the chosen one it squirts up like a missile, spiraling counter-clockwisely until past the thermocline, where the gametes are synchronously released.
Here too the process is not always mathematical. The chosen females, for instance, are sometimes two (or more?), or the male can perform its spiral successively with different mates. At times the spiral can even be a “fake”, that is, it doesn’t end up with the emission of the gametes.
Such gametes, by the way, are immediately preyed upon by other fish (this fact is again not so rare underwater). Especially the saddled seabreams (Oblada melanura), who can “feel” the horny groupers and get ready to hurry upon the sperm-and-eggs cloud. The few surviving fertilized eggs will stay pelagic (that is, they will be pushed around passively by the currents) for about a month, before tiny little groupers will be able to swim and settle in a very shallow place, preferably with pebbles and small rocks. Mind that those babies might eventually live up to 50 years!
The other amazing feature about the dusky grouper are the changing color patterns. In the picture the scientists have identified up to 8 of them. The first two are the “regular” ones, the following three depend upon the fish attitude (fear, aggressivity) and can be switched in a matter of seconds!, whereas the sixth is the typical one of the large dominant male – the one with the harem. The meaning of the last two patterns is less clear.
Goldblotch grouper (Epinephelus costae)
Let’s discuss the goldblotch grouper (Epinephelus costae) now, who – just like the mottled grouper – is fond of the warmer waters of the Eastern basin and the southern coasts of the Mediterranean. Both species are indeed quite common in Sicily, whereas they’re rare in Northern Italy or in France. The goldblotch grouper too changes sex, at approximately 6 and again depending on the social context. As the dusky grouper – especially the male – is lonely and extremely territorial around its den, the goldblocth grouper is a bit more of the nomad kind: not only it sometimes stays far from the bottom, but it fancies even little group walks.
We experienced directly a couple of weird encounters, the protagonist being always a relatively young specimen. The fish would point right to our mask until physically touching it with its mouth, and would continue to follow us even when we decided to move on.
As for the color patterns, youngsters and females have 5 or 6 lighter brown characteristic longitudinal bands. Yet they disappear in the dominant male, who in turn gets a very clear belly and an unmistakable yellow blotch right behind the operculum (the part of the body covering the gills), like in the picture.
Mottled grouper (Mycteroperca rubra)
Finally, the mottled grouper (Mycteroperca rubia) has a darker body with grayish blotches,
is much narrower, and its inferior jaw is so prominent that it reminds us of Marlon Brando’s “Godfather”. The most distinctive feature is anyway its social behavior, as it prefers to stay in schools like in the video, hanging out far from the bottom while scaring the small fish. Like the other groupers it is an hermaphrodite protogynus but does not have as impressive color pattern changes.
The three species of grouper feed on small fish and crustaceans, and molluscs. The goldblotch grouper also likes ascidians. Their favorite meal is probably the octopus (a cephalopod mollusc indeed). Our experience tells us that where the groupers are abundant it will be hard to spot an octopus: either because only a few survive our beloved groupers’ appetite, or because they would rather hide carefully in their dens.