Most fish species are hatched/born complete for lack of a better term.Polypterids when hatched are not complete and go thru a larval
stage like frogs strange connection but hey.When newly hatched the fry are still developing while you can see the mouth its not functional for the first 18-20 hours after hatching so the external gills allow for respiration.or the first few days after hatching the fry pretty much lay in one spot feeding off a yolk sack as they finish developing this lasts 6-7 days after which you have a developed baby Polypterid-Anne