405_April_24

MARINE BIOLOGY WITH MIKE SCOTLAND - FISH IDENTIFICATION There is the male first fish such as the Damselfish. However, the majority of fish are female first and they change sex into males as they mature. Clownfish are the best example of male first juveniles which change sex into dominant females. The dominant female has one mature male mate and her ‘harem’ of juvenile immature males.

Groupers and Parrotfish do it the other way around. Most dominant males started life as females. Leatherjackets have ovaries or testes but never both. Boys will be boys forever, the same for girls. The importance of fish being able to change sex has to do with survival. If all the males are wiped out, the dominant female can change into a male and mate with her younger sister, thus ensuring the survival of the species. This is an incredible adaptation to survival in the wild ocean. Presumably, Leatherjackets do not have this environmental pressure and so remain the same for life. I saw six tiny ‘Mimic Saddled pufferfish’ on the Ribbon Reefs on a dive in the early 90’s. They were all identical in colour except that two of them had a full see through dorsal fin running along most of the dorsal surface. This is typical of Leatherjackets. The other four had the silly little tiny Dorsal fin of the Pufferfish and Toadfish family, a fraction of the size. This is typical of Pufferfish. This distinction is diagnostic and is an important clue to distinguishing the difference between the two totally unrelated species. You can only see this dorsal fin if you take a closer look! It is tiny and translucent. However, the difference is there if you have the eyes to see. There were actually two Leatherjackets and four Pufferfish in this group. The Leatherjackets had evolved identical colour patterns to Pufferfish to benefit from the fact that fish do not eat the toxic puffers. What a mind blowing moment in diving this was for me. As we used to say in the sixties, “ it blew my mind! ” and it proves that magic does happen in the sea. Next time you see Leatherjackets take note of the long dorsal fin. Same for the Tropical Mimic Leatherjackets

Fijian Tesselated leatherjacket.

Male Six Spined leatherjacket

A male Yellowstriped leatherjacket, Meuschenia flavolineata

The beautiful Stars and Stripes leatherjacket, Meuschenis venusta.

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DIVE LOG Australasia #405 - April ‘24

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