The Fish That You need to Know About
Our idea is that the flexible throat jaws of cichlids allow the survival of many species in the same area. Throat jaws are an extra pair of jaws in the back of the throat. they consist of the reshaped bones of the posterior gill arches and they have teeth, like the jaws in the mouth. It is useful to have two pairs of jaws, as one can be adjusted to accommodate food intake and the other pair to shred food. These two tasks can thus evolve independently of each other
Bite and scrape
Schematic representation of the throat jaws of sunfish (Centrarchidae). Epibranchial 4 is the bone located between the upper and lower jaws and which rotates (caused by contraction of the muscles with force F2 and F3) moving both the lower jaw upwards and the upper jaw downwards, causing the prey is a biting force.
- In African Cichlids there is no rotation and the muscles of F2 and F3 only pull up the lower jaw. In bass, there is only one type of bite movement for each species, a horizontal scrape movement (1), a vertical bite movement (2) or something in between (3). With cichlids the bite directions of (1), (2) and (3) are possible for all species, due to the decoupling of the movement of the upper and lower throat jaws.
- To better understand the role of the pharyngeal apparatus in the evolution of the cichlids, we investigated the pharyngeal apparatus of their suspected ancestors. The ancestors probably looked a bit like bass and American sun bass. We therefore conducted research on the throat jaw apparatus of bass.
- At first glance, this pharyngeal device resembles that of cichlids, because they have the same bones and muscles in roughly the same places. But the device moves in a completely different way. In sun bass (and many other perch species) the upper jaw goes down during chewing and the lower jaw rises a little at the same time. Thus, the food is made small between the jaws. In cichlids, the lower jaw rises and presses against the food and the upper jaw. The upper jaw is in turn pressed against the skull.
Both types of fish use the same muscles to close the jaws. But in cichlids, these muscles only pull up the lower jaw, while in bass, they pull up the lower jaw while simultaneously pushing the upper jaw down. The movements of the lower and upper jaws are linked to bass, but not to cichlids.
The difference is in a small bone. In bass, the muscles are not directly attached to the upper and lower jaw, but to a bone between the two jaws. This bone rotates when the muscles contract. The top turns down and then pushes the upper jaw down like a hammer. the bottom rotates upwards and pulls the lower jaw along. In cichlids this bone is missing and the muscles only pull up the lower jaw. As a result, the movement of the upper and lower jaws is uncoupled. The upper jaws can be moved from front to back by separate muscles.