Disuse, on the other hand, will account for the less developed condition of the whole inferior half of the body, including the lateral fins; though Yarrel thinks that the reduced size of these fins is advantageous to the fish, as "there is so much less room for their action than with the larger fins above."
Erabilerarik ezak, bestalde, azalduko du azpialdeko gorputzerdi guztiaren garapen eskasagoa, alboko hegatsak ere barne, nahiz eta Yarrell-ek uste izan hegats laburrak izatea abantailatsu zaiola arrainari "espazio txikiago dutelako beren lanerako, gaineko hegats handiagoek dutena baino".