SawfishPristidae

Some sawfish are born without a father. Researchers sampling young fish in a 🇺🇸 Florida river found healthy juveniles whose genes came from the mother alone, females having produced offspring with no mating involved at all. It had been seen before in captive sharks and rays, where a lone female has no other option, but this was the first time vertebrates were caught doing it in the wild. The likeliest explanation is also the least encouraging one: the population has thinned to the point where a female can go a season without meeting a male.

Sawfish have lost more of their former range than any other family of marine fishes. They were ordinary animals of shallow coasts, estuaries and river mouths right across the tropics, and they are now gone from most of the countries that had them, because a shallow-water animal carrying a toothed rostrum is caught by any net it touches. One species runs hundreds of kilometers up rivers and can spend years in fresh water, which did not save it either.

The young are born with the saw already full-sized, which is a mechanical problem the mother solves in advance. The rostral teeth are soft at birth and the whole rostrum is wrapped in a membrane that holds it flat and harmless until the pup is clear. Those teeth are not teeth, either. They are enlarged skin denticles set into the sides of the rostrum, and unlike the teeth in a shark's mouth they are not replaced: a sawfish that breaks one off has lost it permanently.

They are rays and not sharks, with gill slits underneath and pectoral fins joined to the head. One species is listed for this sea, the longcomb sawfish, historically present on shallow sand and seagrass along these coasts. Realistically it is gone from the water divers use, and a credible sighting anywhere in the region would now be news rather than a dive report.