MAIN IDEA: What are the main external and internal

anatomical features of fish?

• EXTERNAL ANATOMY

• Morphology or structure and form of fish can affect feeding and type of culture facility. For example, fish with small, upturned mouths generally are herbivores (plant-eating) and/or surface feeders like tilapia. Fish with downturned mouths are generally bottom feeders like catfish.

• Single-lobed or homocercal tail fins suggest that fish are slow swimmers and survive well in water free of much movement. Fish with forked or heterocercal tail fins are fast swimmers and prefer flowing water.

• The body shape of fish also suggests the type of culture facility to use. Fish like trout, with a body long and tapered towards the ends, are the best swimmers and need water space.

• Fish that are wide and flat or tend to stay on the bottom require lots of bottom space for growth. Fish that are rounded and thin from side-to-side or laterally compressed tend to hover in the water

• Body Regions: • Body regions of a fish include: 1) the head

which runs from the tip of snout to the posterior edge of the operculum (the covering over the gills); 2) the trunk (from the operculum to the anus); and 3) the tail (from the anus to the end of the caudal fin).

• Fins:

• Fins on a fish include the single dorsal fins, the anal fin and the caudal (tail) fin; and the paired pectoral and pelvic (ventral) fins.

• Other Structures:

• Other important external structures include teeth in some fish, the nostrils or nares, the eyes, the mouth, the operculum, scales, the lateral line, the anus and the urogenital opening between the anus and the anal fin.

• Scales:

• Many fish are covered with bony or horny shaped plates called scales. These occur on the sides of the fish in overlapping rows. Some fish like catfish do not have scales.

• Surfaces: • Any discussion of the structure and

function of fish must entail an understanding of surfaces: dorsal, ventral, anterior and posterior.

• Dorsal pertains to the upper surface of a fish.

• Ventral relates to the lower or abdominal surface

• Anterior applies to the front or head of a fish.

• Posterior or caudal pertains to the tail or rear of a fish.

• These surface names can be used to describe the location of external structures, locate sites for injections and describe the movement of fluids

• PHYSIOLOGY AND ANATOMY

• Physiology, or the function of fish, occurs in nine body systems adapted to the water environment. These systems include:

• Skeletal • Muscular • Digestive • Excretory • Respiratory • Circulatory • Nervous • Sensory • Reproductive

• Skeletal System:

• The skeletal system is the rigid framework giving the body shape and protecting the organs. It is composed of bony or hard material and cartilage. Tissues and organs attach to the skeleton. Fish possess an internal skeleton, also called an endoskeleton.

• The head is composed of about 40 bones. The skeleton surrounding the body organs forms a compact movable support for the gill mechanism. Pectoral fins join the pectoral girdle that attaches dorsally behind the head. The pelvic fins move on two flat bony plates lying in the ventral trunk muscles.

• The vertebrae are more delicate, proportionately, than those in most land vertebrates. The vertebral column ends in several stout flat bones supporting rays of the caudal fin.

• The dorsal and anal fin rays articulate on intramuscular bones that alternate with the long dorsal and ventral spines of the vertebrae. Paired slender rib bones attach to each trunk vertebra.

• Muscular System:

• The muscular system provides movement internally and externally. Muscles vary in strength and function. Muscles contract and relax to cause movement. Fish require movement for such functions as obtaining food and oxygen and for eliminating wastes.

• Muscles on the sides between the anal and caudal fins are divided into muscle segments in what looks like a sideways shaped "W" extending from mid-dorsal to a mid-ventral line.

• Each segment is separated from those adjacent by connective-tissue partitions. A lengthwise partition beneath the lateral line separates each segment into dorsal and ventral parts.