aspects of fish biology form and function

301a
The fish eaters (piscivores) usually possess strong flat, closely
set teeth, which may be acutely sharp and pointed and ideally suited for
capturing and holding live fish (e.g. the snoek, Thrysites atun).
However, some piscivores such as the kingfish (Seriola grandis) have
relatively fine brush-like teeth. These still meet the requirements of
grasping and holding struggling prey. Others like the blue cod
(Parapercis colias) have surprisingly small teeth, or even toothless
mouths; however, thev have sharp well developed pharyngeal teeth.
Invertebrate feeders and herbivores exhibit a vast array of teeth, the
type dependinq on the food they eat. Small pointed cone-shaped teeth
at the front of the jaw are used to pick invertebrates from the substratum.
Some species also possess blunt molar-like teeth further back on the jaw
(the sparids e.g. Chrysophrys auratus) , or in the throat (the labrids,
e.g. banded wrasse, Pseudolabrus fucicola) to crush hard shells. The
herbivores usually have bands of small notched teeth in the jaws and some
have a series of chisel-like incisors for cutting or scraping algae from
the rocks. The teeth of the plankton eaters are small and feeble, or may
be absent altogether. These fish typically possess elaborate structures
known as gill filaments, which strain the microscopic organisms
out of the water they take into their mouths before it passes over the
gills. These double rows of stiff, interlocking appendages are situated
on the inner marqins of the gill arch (see figure 9). In most fish they
exist as bony knobs but in the planktivorous fish they are long, numerous
and closely set with many secondary and tertiary branches.
Generally the teeth are single structures. However in several
groups, the teeth in the jaws are fused together. The teeth of the
parrotfish (scarids) are fused to form a beak for cutting off pieces of
coral and seaweed. In other groups the fused teeth form a single or
double plate in each jaw as in the families Diodontidae and Tetradontidae.
These plates are sharp at the edge and also provide a broad crushing
surface within.
Skin9 scales and spines .
Fish have a skin composed of two layers. The outer layer, or
epidermis, is composed of cells which are constantly being warn away and
replaced by new ones developing at the base. Underneath is the dermis,
a thick laver of connective tissue, muscle fibres and mucous glands.
Fish also have an outer covering of scales. When these are absent the