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Lab. -12-
The fishes
Practical Biology
*Bony Fish
A bony fish is aquatic vertebrate animal with skin covered with scales. It lives in
water and is usually oviparous.
** Characteristics of bony fish:
1- General form of the body, is bilaterally compressed along it is entire length.
2- The eyes are large; the eyelids are absent. Two small nostrils lie in front of the
eyes.
3- The operculum or gill-cover on each side of the head formed of two
portions, a large anterior bony portion supported by bones connected to the bones
of the skull, and small posterior membranous portion.
4- Fins: the fins of most fish are supported by rays or spines. Rays are flexible,
spines are rigid. The types of fins are unpaired like: (dorsal, caudal, and anal)
; paired like (pelvic fin and pectoral fin).
5-Skin: Skin with many mucous glands, usually with embedded bony scales of
mesoderm origin. (Some are scale less). Scale are thin, round disk of a bonelike
material, the scales protect the body of a bony fish and reduce friction when
swimming.
6- Lateral line: central line dividing a fish lengthwise.
7- Swim bladder: The swim bladder is a balloon like thin-walled sac in the abdominal
cavity that contains a mixture of oxygen, carbon dioxide, and nitrogen obtained from
the bloodstream that is used to control buoyancy.
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**Internal Anatomy:*Skeletal system:
The major parts of a fish’s skeleton are the skull, spinal column, pectoral girdle,
pelvic girdle, and ribs.
*Digestive system
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1- The mouth is terminal and small; and it is surrounded by two jaws and the
pharynx, is not distinguished from the mouth, the two forming a common
buccopharyngeal cavity.
2- The esophagus, is short, the stomach is described as being of the caecal type,
consisting of cardiac portion extended backwards into a blind sac or which serves
to store the food. The pyloric portion of the stomach is small and shifts ventrally.
3- The intestine, is a very long coiled tube, note that there is hardly any external
differentiation of the intestine into duodenum, ileum and rectum.
4- The liver is large, bilobed, dark red in colour; the left lobe is much larger than the
right lobe. The gall-bladder is a membranous spherical sac, which is lie anteriorly
at the level of the pylorus.
5- The pancreas is either compact gland in some fishes or on form of microscopic
alveoli scattered in the adipose tissue of the mesenteries.
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