Question

What are two ways other than development of a gas bladder that fishes use to stay neutrally buoyant, and what is the general shortcoming of these methods?

Answer 1

Osteichthyes or bony fishes posses a specilized structure, which help them to maintain the buoyancy and make equilibrium in water, this structure is known as gas bladder or swim bladder. It is two types, physoclistous (coonected through duct) and physostomous (not connected) . The major different in these two structures is on the basis of their connection with gut. Physostomous is connect to the gut (esophagous) through a duct (known as ductus pnematicus), whereas there is no connection in case of physoclistous.

All bony fishes possess physostomous type of gas gland during the development (larval development). Other functions of this structure are in excretion, respiration and also assist in sound production. Cartilaginous or Chondrichthyes are not having this structure; they possess other strategies like excessive oil in body etc. Even though bony fishes are having this structure but this structure do have some limitation like it cant work at all depths, if fish mover further in depth then they will loose buoyancy and sink and to overcome with this problem they have to invest more energy.