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Definition and evolution of fish
1. Definition of "real fish"
Refers to a group of lifelong warm vertebrates living in water, using gills to exchange gases in water, using fins to maintain body balance, most of them covered with scales, and most of the swim bladders are present.
2. The evolution of fish
Extant fish can be divided into three classes: round-mouthed, cartilaginous fish, and teleost fish
(Round mouth: lamprey eel)
(Cartilaginous fish)
(Bony fish)
Second, the external form of the fish
1. Distinction between the outside of the fish body
(External Pattern)
2. The size of the fish
1. Body shaft
Left and right symmetry, generally with three body axes
(1) Head and tail shaft (first axis or spindle)
(2) Dorsal ventral axis (second axis or sagittal axis) - perpendicular to the head and tail axis
(3) Left and right axes (third axis or side axis) - perpendicular to the first two axes
2. Body type
There are generally four types
(1) Spindle shape (grass carp, mackerel, tuna, etc.)
(2) Lateral flattened (tuantou bream, pomfret, etc.)
(3) Flattened (catfish, rays, etc.)
(4) Cylindrical (yellow eel, eel, etc.)
Spindle (grass carp)
Lateral flattened (tuantou bream)
Flattened (ray)
Cylindrical (yellow eel)
3. Head organs
(1) Mouth
(2) Lips
(3) Whiskers (can be based on the position, shape, length, number of whiskers as a classification feature)
(4) Eyes (no tear glands, no true eyelids, some sharks have instantaneous membranes)
(5) Nostrils (nostrils do not communicate with the mouth, and have nothing to do with breathing)
(6) Gill hole (gill fissure) (breathing-related)
(7) Water spray holes (vestigial gill holes, most fish degenerate)
4. Fins
1. Fin classification and function
2. Fin type
Fin formula ——— taxonomically, a formula for the composition, structure, and type and number of fins of a fish fin. It is one of the identification criteria in fish classification.
The first letter of each fin in Latin represents the name of the fin category:
"D" stands for dorsal fin
A stands for fin
The "V" stands for ventral fin
The " P " stands for pectoral fin
"C" stands for Caudal Fin
The capitalized Roman numerals represent the number of spines (spines). Arabic numerals represent the number of soft bars (fin strips), the range of thorns or soft bars is represented by "~", the spines are connected to the soft bar by "one", and when separated, they are separated by ", ".
Example:
Carp fin type: D.. III.~IV.-17~22;P. I. 15 to 16; VII. 18 to 9; A. III. 15 to 6; C. 20 to 22.
It indicates that carp has a dorsal fin with 3 to 4 hard spines and 17 to 22 soft strips; 1 hard spine and 15 to 16 soft strips in the pectoral fin; 2 hard spines and 8 to 9 soft strips in the ventral fin; 3 hard spines and 5 to 6 soft strips in the fin; and 20 to 22 soft strips in the caudal fin.
3. The skin and its derivatives
1. Skin
1. Fish skin
Divided into two layers
(1) Outer layer - epidermis
a. Layer of occurrence (birthplace of epidermal cells)
b. Glandular layer (except for the occurrence layer, the rest are glandular layers, and there are a large number of glandular cells)
(2) Inner layer - leather
Top-down
a. Outer membrane layer
b. Loose layer
c. Dense layer
2. Glands
Classification and function of fish glands
(1) Single-celled glands (mainly secrete mucus)
a. Goblet cells
b. Rod cells
c. Granulocytes
d. Serous cells
(2) Toxic glands (secrete various toxins)
3. Scales
1. Scaly classification
(1) Shield scales
The placoid scale, endemic to plate gills, is formed by the epidermis and dermis, and the structure is divided into two parts: the substrate and the scaly spine. The substrate is made up of dentist, usually in a diamond-shaped shape buried in the skin. The scaly spines are exposed on the outside of the skin, the tip is facing backwards, the outside is covered with enamel, and the inside is dendritic. Inside the scaly spines there are marrow chambers containing connective tissue, blood vessels, and nerves, which resemble teeth in structure, so they are also called skin teeth. Shield scales are generally arranged diagonally.
▲ Shark scales under electron microscopy, the picture comes from the Internet
Plate gills are a taxon of cartilaginous suborder fish, the gills are plate-like, the outer body is shield scales or smooth, and the male ventral fin is transformed into a handicap. Plate gills have 5 to 7 pairs of external gill holes; maxillary cartilage is not attached to the skull or is connected by ligaments; the body is scaled or smooth. The vertebral body differentiates, the cord is contracted in sections, and the left and right halves of the belt heal into one. It has a cloaca. Males have no anterior ventral and upper-frontal flippers.
(2) Hard scales
The ganoid scale, a diamond-shaped bone plate buried under the dermis, derives from the dermis. It is found in polyfinfish and finches. Hard scales are arranged in rows, and adjacent scales can be inlaid with concave and convex surfaces, and there is room for expansion and contraction.
Hard scales can have up to four layers of structure: the hard scales on the surface are fully calcified, and the hard shiny matter with a special luster resembles enamel. Below there is a dentoid-like surface layer of the department, a tube layer with a myelinic cavity, and an inner bone layer composed of parallel bone plates.
(3) Bone scales
The scales of most teleost fish belong to the bony scale. It is composed of bone plates derived from the dermis. The anterior end of the bone scale grows in the scale sac, and the posterior end is free and arranged in a tile-like manner. Bone scales do not change for life but can grow as the fish grows. The concentric rings on the bone scales due to changes in growth rate are called annual rings. In the northern hemisphere, fish grow fast and have wide rings in spring and summer; slow and rings in autumn and winter; so there are two groups of rings between the year. The rings can be used to judge the age of fish, growth rate, etc.
Teleost fish have bony scales, formed entirely from the dermis. Bone scales can be subdivided into hard scales, round scales, and ctenophores. Typical representatives with hard scales are sturgeon, garnets and multi-finned fish, etc., whose scales are very hard and diamond-shaped, and the scales are closely connected by fibers between the scales and the scales.
▲ Types of fish scales, A. shield scales (sharks); B. hard scales (garnets); C. round scales (carp) ;D. Chestnut scales (yellow perch)
Bone scale classification:
There are two types of shapes:
a. Round scales: found in salmon, carp, etc.
b. Ctenophores: found in perch and so on.
Round scales and ctenophores can also be found in different parts of the same fish body, such as semi-slippery tongue rays with ctenophores on the ocular side and round scales on the non-ocular side. They can also be found at different stages of the same fish body, such as the juvenile of the herring carp is round scaled, and the adult fish is ctenophoric scales.
2. Lateral line with scales
(1) Side line
On both sides of the body of the general bonefish, there is a linear structure arranged by small holes in the scales, called the lateral line.
(2) Scaly
Refers to the arrangement of fish scales. Scales vary from species to species and become one of the criteria for classification and identification.
The scale pattern is written in the × of the lateral scales (the number of scales on the lateral line÷ the number of scales below the lateral line).
For example, the phosphorus formula of carp is 34 ~ 38 5/8. The lateral scales (scales passed by the lateral line hole) of the carp are 34 to 38, the lateral linear scales (horizontal scales from the lateral line to the front of the dorsal fin) are 5, and the lateral lower scales (horizontal scales from the lateral line to the base of the fin) are 8.
4. Pigment cells and body color
1. Pigment cells
(1) Basic pigment cells
a. Melanocytes
b. Xanthoblasts
c. Red pigment cells
The combination of the above three cells can produce a variety of colors
(2) Other pigment cells
a. Iridescent cells, etc
Changes in the movement of pigment cells are regulated by neural and hormonal control
2. Body color
Body color plays a protective role and covers the role of predation
5. Illuminator
1. Fish glow mode
(1) Symbiosis with luminescent bacteria
(2) Luminous glands emit light independently and autonomously
2. Composition of the illuminator
The perfect light emitter is mainly composed of a luminescent gland, a lens, a reflector and a pigment cover
Fourth, the skeletal system
The bone arm originates from the mesodermal mesophyll tissue.
There are certain areas of the growing bone arm, and the main bone growth areas are:
(1) Skin zone 1 produces scales and their derivatives;
(2) Horizontal diaphragm area, located between the upper and lower axial muscles on the body side, such as the dorsal ribs in this area;
(3) Dorsal bone septum and abdominal bone septum: the fin bones of the odd fin are born in between;
(4) The muscular septal zone (located between the two muscle nodes), in which the intermuscular bone is born;
(5) Around the chordal cord, neural tube and central axial vascular area, the cranial and spinal glands are formed in this area;
(6) Pharyngeal cranial area: the formation of pharyngeal cranial bones;
(7) Appendage area: the formation of appendage bone arm.
1. Spindle bones
1. Skull
(1) Cranial brain
(2) Pharyngeal cranial
There are differences between teleost fish and cartilaginous fish.
2. Spine and ribs
The vertebrae of the carp
Calcium is often precipitated in the cones of cartilaginous fish, which enhances firmness. There are three types of calcium precipitation styles: (1) single ring: there is only one calcification ring
(2) Multicyclic: two or more calcification rings
(3) Star ring: single ring calcification circle plus some radiation calcification strips
Vertebrae can be used to identify age and analyze intraspecific populations.
It should be noted here that the names of certain bones have changed now, and attention should be paid to distinctions.
ribs
(1) Dorsal ribs, also known as intermuscular ribs
(2) Abdominal ribs, used to support the abdominal cavity
2. Appendage bones
1. Odd finned fin bones
The typical representative, shark fin, is supported by the fin bone
2. Caudal fin classification
Classification is based on the symmetry of the upper and lower fin lobes of the caudal fin and the location of the inner spine:
(1) Prototype tail
(2) Crooked tail
(3) Positive tail
(4) Spear-shaped tail
2. Even finned fin bones and band bones
Rainbows, rays and shark straps differ in that the upper end of the shoulder straps of the first two types, that is, the end of the shoulder blades, is connected to the sides of the upper spine of the spine, while the sharks are free in the dorsal muscles.
The even-fin bone arm of teleost fish has the following changes:
(1) Ossification into pieces of hard bone on the basis of cartilage, and at the same time added membrane bone;
(2) The fin bones are not large, and the number is reduced or even completely disappeared (healing).
Therefore, the relationship between the bone supporting the fins like the cartilaginous fish, that is, the bone supporting the fin bone, and the supporting fins of the bone no longer exists or does not fully exist, but the phenomenon of cross-level support occurs.
Fifth, the muscle system
Muscles are mainly divided into three main categories:
(1) Smooth muscle
Exists in connective tissue and is not governed by will
(2) Heart muscle (myocardium)
Uncontrolled, rhythmic
(3) Striated muscle (skeletal muscle)
Contact the bone, can be actively controlled.
1. Naming of muscles
1. Basis of naming
(1) The raw part
Such as: intergill anticlinal oblique muscle, etc
(2) Starting and ending points such as: tail spoon muscle, etc
(3) The action function is divided into the following points
a. Adductors
b. Spread the muscles
c. Extensor
d. Laminar muscles
e. Levator muscles
f. Muscle lowering
g. Traction muscles
h. Pull (retreat) muscle contraction
i. Open muscles
j. Muscle contraction
(Lateral and segmental muscles of fish)
2. Categories and functions of muscles
1. Head muscles
Many muscle names express function. In addition to the head muscles in the picture above, there are the following:
(1) Tongue muscles:
a. Frontal tongue muscles
b. Tongue muscles
c. Pectoral and tongue muscles
(2) Eye muscles:
a. Rectus superior
b. Rectus inferior
c. Rectus internalis
d. Inferior oblique muscle
e. Superior oblique muscle
f. Rectus externalis
2. Trunk - tail muscles
(1) Large lateral muscles, which can be divided into:
a. Red muscle Is high in fat and has blood circulation
b. White Muscle The largest muscle in volume, free of fat
It is mainly used for sports and commodity consumption
(Fish lateral muscle tissue section)
(2) Prismatic muscles, which can be divided into:
a. Superior prism
b. Inferior prism
3. Appendage muscles
(1) Pectoral fin muscle
(2) Abdominal fin muscle
(3) Dorsal fin muscle
(4) Caudal fin muscle
3. Power generation organs
Power-generating organs are metamorphs of muscles, and only a few fish have power-generating organs. Its functional unit is electrical cells, which are generally developed from the central axial muscles and are more common in the tail.
Sixth, the digestive system
1. Body cavity and mesangium
The body cavity of fish is divided into periocentric and abdominal chambers by the periapical diaphragm.
Mesangial species
Gastric-splenic mesangium, gastric hepatic mesangium, spermatozoal mesangium, ovarian mesangium, etc
2. Digestive tube
1. Oropharyngeal cavity
There are teeth, tongue, gill rakers and other structures
(Pharyngeal teeth comparison of bluefish and grass carp)
(1) Classification of bony fish teeth
a. Canine teeth : Sharp and multi-carnivorous fish
b. Conical teeth: Slender and sharp teeth, succulent fish
c. Molar teeth: fish that feed mostly on snails
d. Incisor-like teeth: prey on organisms fixed on rocky reefs.
(2) Tongue
Most fish tongues are primitive, located at the base of the mouth, inelastic, muscularly underdeveloped, inactive, and covered with mucous membranes. Different shapes.
(3) Gill rakers
As the leading edge of the filter feeding organ, the taste buds can feel the sense of taste. Gill raker species are also very diverse. Different gill rakers can evolve depending on the type of food.
2. Esophagus
The fish esophagus is short, wide and straight, with thick tube walls, and consists of the mucosal layer of the inner layer, the muscular layer of the middle layer, and the outer serous layer.
3. Stomach
Most fish are stomachless, and most carnivorous fish have stomachs. The largest part of the digestive duct is located behind the esophagus, with the cardia near the esophagus and the pyloric part near the intestine. Generally, the stomach has four layers: the innermost mucosal layer, followed by the submucosal layer, the muscle layer, and the outermost serous layer.
(1) Classification of fish stomachs
a. I型
b. U型
c. V型
d. Y型
e. Bu type
(2) Classification of the mucosa in the stomach
a. Parallel folds of the vertical walk
b. Longitudinal meandering
c. Transverse folds between the longitudinal folds
d. Longitudinal pleats between the longitudinal folds
e. Reticulated folds between the longitudinal folds
f. Mastoid between the longitudinal folds
4. Intestines
The tissue of the intestinal wall resembles the stomach wall and is divided into the mucosal layer, the submucosal layer, the muscle layer and the serous layer.
(1) Classification of intestinal mucosa:
a. Longitudinal folds
b. Transverse folds
c. Transverse jagged folds
d. Reticulated folds
(2) Classification of the large intestine
a. Colon
b. Rectum
(3) Classification of small intestines
a. Duodenum
b. Ileum
(4) Pyloric blind sac
Increases the absorption area, secretes joke substances
3. Digestive glands
The digestive glands are mainly divided into:
(1) Gastric glands : a small number of fish degenerate
(2) Intestinal glands: most fish are deficient
(3) Liver: the largest and most useful digestive glands, some fish liver pancreas mixed together collectively known as hepatoscreas, the digestive juices secreted by the liver are usually stored in the gallbladder.
(4) Pancreas
Most fish have a well-developed pancreas, located at the end of the stomach where it meets the intestine. A portion of the glands are diffuse into the liver. Secretes digestive enzymes that promote food breakdown, and some have islet cells that regulate blood sugar.
Seven, the respiratory system
1. Gills
The construction of gills
1. Outer gills
It occurs in the embryonic or juvenile stage of some fish, and is divided into two types: endodermal gills and ectodermal gills.
2. Pseudogills
For example, the water spray hole is a pseudo-gill
Pseudogills generally fall into two categories:
(1) Free pseudogill: The anatomy is no different from the true gill, but it is relatively small. Such as water-jet hole gills.
(2) Embedded pseudogills: Embedded in connective tissue is not easy to identify, only seen in eukeletal fish.
2. Breathing exercises
Achieved by the action of the oral pump and the gill cavity pump, it is mainly divided into two processes:
(1) Expand the water absorption process
(2) Compressed water effluent process
3. Auxiliary respiratory organs
In order to absorb oxygen in special circumstances, some fish will specialize in some auxiliary respiratory organs, mainly including skin, intestinal tubes, oropharyngeal mucosa, supragill organs, air sacs and so on.
4. Maw
1. Construction
It generally consists of two parts:
(1) Body (front chamber): Main part
(2) Airway
a. Oval chamber
b. Maw tubes
The swim bladder receives a double innervation of the vagus nerve and the sympathetic nervous system. In some special fish, such as the African lungfish maw is bilobited, has air ventricles (alveoli) and several small air sacs (alveoli), similar to the lungs doing breathing exercises.
2. Features
The main functions are as follows:
(1) Regulating density: The fish's ups and downs mainly rely on muscles and fins, but the maw can be used as an auxiliary role to reduce energy consumption.
(2) Respiration: Low-grade teleost fish such as lungfish, garnets, etc. have secondary functions.
(3) Sensory effect: In the order Cyprinid, the fish Weber's apparatus is a set of small bone pieces that connect the swim bladder and the inner ear, which allows the fish to perceive a certain frequency to obtain a keen perception.
(4) Vocalization: Some fish produce sound through the deflation of the swim bladder tube.
(Note: This article is for reference and communication only!) Most of the content and pictures come from network information, if there is any disagreement, please inform, welcome to correct and leave a message to discuss)
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