The biology, morphology, and distribution of barracuda According to Thompson (1954), there are 281 species that have been reported by the Mugilidae family, but there are many different species, of which there are about 70 species. . In China, there are 7 species and 28 species recorded, but the main targets for breeding are salmon and barracuda. (I) Morphological characteristics 1. Mugil soiuy, also known as meat sticks (Liaoning, Hebei), red-eye fish (Shandong), red-eye fish, red-eye (Zhejiang, Fujian), Zhaiyu (Guangdong), etc. Cylindrical body, gradually flattened back, head short and wide, eyes smaller, fat eyelids underdeveloped. Eyes are red and yellow. The base of the pectoral fins is free of scales. The caudal fins are slightly concave on the trailing edge. The back is grayish-gray with light gray on both sides, light gray on both sides, ventral white, and black stripes on the scales on the side of the body. (b) Distribution The carps are very widely distributed, and almost all of them can be found in the world. However, tropical and sub-tropical waters are the most abundant species. They are not only species but also large in quantity. It is the most widely distributed in the temperate, tropical and subtropical coastal waters. It is distributed in all sea areas and coastal estuaries in the five major European, Asian, U.S., U.S., and U.S. states, and has become one of the most widely distributed fish species in the world. Important economic fishes in the Atlantic, Pacific, Indian Ocean, Mediterranean and Black Sea. Polygonidae are distributed in the coastal areas of China, from Hainan Island in the south, to Lushun and Dandong in the north, and the number of brackish and freshwater domains with lower salinity in Inner Bay is more. The general trend of distribution is that there are fewer species in the north and more species in the south, and the South China Sea and Taiwan, in particular, have the most species and yields are most abundant. The most common carp and barracuda are widely distributed in the South China Sea, the East China Sea and the Yellow Sea. The squid is more in the south and has a certain amount in the coastal areas of Shandong. The barracuda is more in the north and the Bohai Bay and the Yellow Sea are more dense along the coast. Second, the ecological habits (a) of the adaptation of the environment Barracuda tropical shallow sea, middle-level fish, hi living in coastal nearshore, estuaries, bays and other salty waters, but also with the tide into freshwater. Barracuda adapts to a wide range of salinity and can live in seawater, brackish water and pure water. Barracuda can live from 38 inches of salt water to pure fresh water. Based on the wide salinity of barracuda, it can also be cultured in freshwater ponds, reservoirs and lakes, in addition to seawater and brackish water. Barracuda is a warm-blooded fish, but its adaptability to water temperature is also wide. Barracudas can live in the water at 1-30°C. The optimum water temperature is 12-25°C and the lethal low temperature is 0.7°C. Barracuda has a strong ability to adapt to changes in water temperature. For example, in barnacle artificial breeding, water temperature gradually increased from 15.8°C to 30.2°C in 30 days without any discomfort. The larvae can tolerate 7-9°C. Daily changes, no adverse effects. Barracuda can also be adapted to changes in water quality, such as barracuda can still endure in dissolved oxygen of 0.9mg/L of water. (2) Feeding Habits Barracudas have a wide range of feeding habits and are omnivorous fishes that are mainly feed on plants. It mainly uses benthic diatoms and organic debris deposited on the sediment surface, and also eats some filamentous algae, copepods, polychaetes, molluscs, and small shrimps. Under artificial breeding conditions, we also like to eat rice bran, bean cake powder, peanut cake powder, dried leeches and artificial diets. Barracuda feeding intensity, there is day and night, season, individual differences. In the daily cycle, both day and night feed, but usually the intensity of feeding before and after dawn and before and after sunset is greater than at night; during the growth cycle, barracuda 20-40cm body length feeding intensity; before the reproductive period, the intensity of ingestion Large, esophagus, and stomach are always full of food. During the reproductive and spawning seasons, they rarely eat and eat. From the seasons point of view, spring is not the beginning of the summer and autumn is the season of strong feeding, and in the winter, as the water temperature decreases, the fish enters the wintering period, when the fish eat very little or stop feeding. (c) The migratory barracuda is a semi-migratory fish that has no long-distance migration. However, it can be used as a short-distance and small-scale migration movement with the season, water temperature and its own development. Squid often inhabits shallow sea or estuary depth of 1-16m, when the weather becomes cold, then swim to the deep winter. But individual winters also occur in deeper bays and shallow seas. Squid spawned in deeper sea areas, and the hatched young fishes drifted to the near-shore estuary with the tide and stayed at the salt-freshwater confluence to feed and grow. Barracudas generally grow in the coastal waters and form large groups to spawn in the bays and estuaries on an annual basis. From June to July, a large number of juvenile fishes appeared on the coast of the Yellow Sea and Bohai Sea and entered the mouth of the river. During the cold days, they swim to deeper sea areas for winter. III. Growth (a) Growth of barracuda According to the report of Li Mingde et al. (1978): The barracudas collected in the Qikou area of ​​Hebei Province have a maximum age of 8 years, a maximum body length of 720 mm, and a weight of 4600 g. The growth of barracuda varies between different age groups. In the same age group, the range of body length and weight changes are also larger. In general, when the young shuttle grows more slowly, the average weight is 50g, and it enters the peak of growth from the second year until the 6th year, especially 3 to 5 years old, and grows most rapidly. Slow down after age 6. The fullness and fat accumulation coefficient of each age group of barracuda were the highest between 1 and 2 years old, and then decreased with age. This change is related to the development of gonads in marine barracudas. Because the gonads of 1-2 years old mullets are not yet mature, their food intensity is the strongest. The fullness of the stomach is highest in the sac, and fat accumulation is more, so the fullness is higher. After the 3rd and 4th instars, the gonads of the barracudas gradually matured and consumed a lot of fat due to the nutrients needed to supply the gonadal development. So in barracuda culture, the winter of the second and third year is sold as commercial fish, and the value of food is the highest. Coupling coefficient (%) = fat weight / (body weight - visceral weight) 100 Barracuda female and male sex differences in growth, in the young age is not obvious, but as soon as the gonads begin to mature, it is significantly reflected, 4-year-old female Fish, regardless of body length, body weight, and fullness, are larger than males. It can be seen that females of barracudas grow faster than males. The growth rate of barracuda is greatly affected by the food environment. The proper amount of individuals is mixed in the shrimp pond, and its growth is much faster than that of the natural sea area. IV. Reproduction Biology (I) Sexual maturation age and fecundity Barracuda reaches the age of sexual maturation. The male fish is 2 years old, with a large number of 3-4 instars, 3 female instars, and a large number of 4 instars. In the barracuda of Xiangshan Port in Zhejiang, the earliest age at which males reached sexual maturity was 1 winter, while females were 4 years old. The female body is 44cm long and weighs 1580g when it is sexually mature. The male body is up to 32.5cm in body weight and matures at a weight of 450g. The weight of the IV stage of the ovary fluctuates between 230 and 2200 g depending on the size, age, and maturity of the fish. The amount of fleshes also increases with individual, age, and weight, typically 1.5 to 4 million. The barracuda in Hebei Huangpi area has a fecundity of 301,100 to 3,115 thousand. The barracudas in Liaoning Province have a fertility of 300,000 to 500,000 eggs per side of 1.5kg. (B) Gonadal development Fish gonadal development, maturation and spawning processes are strictly cyclical. When the first spawning is achieved, the gonads change regularly according to the regularity of the season, and the cycle does not change. . Barracuda is a fish that reproduces once a year. In order to facilitate comparison and understanding of the maturity of gonad development, artificially divide the gonad development process into several stages. According to the external morphology and internal structure of the gonads, the development of fish gonads is generally divided into six phases. Barracuda is now described as an example as follows: Part I: For juveniles who have not reached sexual maturity. The gonads are transparent and thin lines, close to the dorsal side of the body wall, the naked eye can not distinguish between male and female, the surface can not see blood vessels. The average maturity factor is 0.0937. Seen from the tissue section, the oocytes containing oocytes and juveniles have a diameter of about 0.07-0.09 mm, a large proportion of nuclei, and one nucleoli, usually located in the middle of the nucleus. Phase II: Sexually mature fish that appear in the beginning of development of sexually immature fish or gonadal degeneration. In sexually immature individuals who first reached stage II, the ovaries are flat, red and transparent, and the ovaries have a thin coat. The vascular distribution can be clearly seen on the surface, and the eggs cannot be separated by the naked eye. The coefficient is 0. 52, and the oocyte diameter is 0.10-0.18mm. After mature egg laying, the ovary returned to the stage II due to degeneration and absorption. It is purple due to vascular congestion. It is opaque. The ovaries have thicker linings, the ovaries have less fullness, appear soft, and a small amount of ovary remains. The 2-4 oocyte transition type of the oocyte. The ovary consists of an oocyte that corresponds to a layer of follicular phase. The cells are round or polygonal. The oldest generation of oocytes have a diameter of 13-179.6 μm, and the nucleus is round, which still accounts for a large proportion. The number of nucleoli increases, about 15-31, ranging in size and distribution along the nuclear membrane. On the outer edge of the oocyte, there is a layer of follicular membrane that is surrounded by a layer of cells, and lipid material appears at the end of the current period. The male testis has a flat, thin band that is 2/3 of its length in the abdominal cavity. Cross cut into sharp triangles with an average maturity of 0.6%. Stage III: The ovary is significantly enlarged. It is cylindrical and pale yellow. The ovary accounts for 2/3-3/4 of the abdominal cavity. The ovum is clearly visible, but the eggs are tightly packed together and difficult to separate. The average maturation factor is 2.369. Vascular traps of the testis of male fish fall into a rosy or pinkish pink, long band, with a length of approximately 3.9% of the abdominal cavity. Oocytes in the ovary enter the large growth stage. The biggest feature is that the diameter of the oocyte is much larger than the previous stage. It was 170-200μm earlier and expanded to 590μm later. Most of the nucleoli distribute on the edge of the nucleus, and a few are located in the center of the nucleus. The spherical yolk granules begin to form on the edge of the egg and accumulate rapidly. However, the yolk is not completely filled in the entire oocyst, and the oil droplet gradually grows from the periphery of the nuclear membrane. In the entire cytoplasm, the egg membrane thickens, with a two-layered structure of the follicular membrane. Stage IV: The appearance of the ovary is thick and it almost fills the entire body cavity. The ovaries are orange and full of blood vessels. In the early days, the granules could not be separated. The granules in the later period are full and easy to fall off and separated. With slight pressure, the eggs can be extruded. Egg diameter is about 600--800 μm. The average maturity coefficient was 7.436 (4.15--14.7). The microscopic morphology of the egg is: yolk granules and oil droplets fill the entire oocyte, according to the changes of oil droplets, yolk granules and nucleus, this phase can be divided into three sub-periods: oocyte of stage IV1 (phase IV), Apricot yellow, oil droplets small, scattered between the yolk particles in the ovum, microscopic examination of live eggs is not easy to see. The nucleus is located in the middle, and the yolk granules increase in size, appearing round or oblong, and are evenly distributed. In stage IV2 (phase IV) oocytes, the oil droplets became larger and concentrated around the nucleus, and a few oil droplets had begun to synthesize, which was clearly visible on microscopic examination of live eggs. The yolk granules became larger and merged with each other. The nucleus was wavy and the nucleus was toward the animal pole. The nucleolus distributed along the trough. The oocytes of stage IV3 (end of stage IV) were orange-yellow, and the oil droplets converged into a large oil globules; the yolk granules merged clearly and the nucleus migrated to the end of the animal pole, ie, the so-called “polarization phenomenon†occurred. Cell size tends to be uniform. Male testes are hypertrophied, milky white and 4/5 in length. The cross section is kidney-shaped, and the abdomen can squeeze a small amount of semen. The average maturity coefficient is 8.4%. Phase V: The ovaries pale yellow, soft and inflated, filling the entire abdominal cavity. The egg is transparent and separated. The egg diameter is about 1mm. An oil ball is very clear, mature egg cells released from the follicle, free in the ovarian cavity. When the fish is gently pressed or the fish is lifted, the egg can flow out. The mature egg was isolated from the follicle membrane. There were oocytes in the first and second phases of the ovary and a few oocytes in the fourth stage that did not leave the nest. At this time, the duration was the shortest among the phases. Hours to ten hours. The testis is milky white and fills the entire abdominal cavity. The head of the fish is lifted or the fish's abdomen is lightly tapped. A large amount of semen flows out. The highest maturity factor is 15.0%. Phase VI: The ovaries that have been spawned for a short period of time or after the spermatorrhea. After licking the eggs, the ovaries shrink, become soft and congested, and appear purple. The ovarian section is in a relaxed state. Due to the expulsion of mature eggs, many gaps are left in the ovary. Some young oocytes can be seen in the section. The oldest phase corresponds to the late phase III and is found in various oocytes. In the gap after ovulation, full of blood, with empty follicles is the main sign of spawning. After the spermatorrhea, the volume of the testis is greatly reduced, yellowish-white, and a small amount of residual semen can be extruded under pressure. The average maturity coefficient is about 3%. (C) The reproductive season and spawning environment The reproductive season of carps, depending on the species, varies from region to region. At the same time, it is closely related to the habitat. According to reports, the breeding season for American catfish is from December to the end of January. In the vicinity of Qinshan Mountain in Haizhou Bay, China, the spawning period of barracuda is from early May to late. The spawning period in Bohai Bay and Huanghua is from the end of April to early June, and is from the sea between Lianyungang, Jiangsu Province to Rizhao City, Shandong Province, in May. A large number of barracuda eggs can be caught in the upper and middle sifter trawls. The spawning period for the barracudas of Zhejiang Xiangshan Port is from the beginning of April to the beginning of May. The spawning is the highest during the first half of April to the middle of the month (from Qingming to Guyu). Peach blossoms, so fishermen are known as "peach blossoms." Barracudas generally grow in shallow seas. When the spring warmth rises, a large number of broodstock swim to the nearshore shallow water area to feed fat and find its spawning ground. Xiangshan Port in Zhejiang Province is a good place for barracudas to lay eggs. The water depth of the port is relatively transparent (1 to 1.5m). The trend in the port is stable and the waves in the harbor are relatively small. Barracuda is the most concentrated spawning area in the sea area around the Lion’s mouth. There is a wide flat tidal flat. The bottom of the tidal zone is mostly muddy. The bottom is covered with rich yellow-brown “oil sludge†with fresh water flowing into the water. A large number of organic substances and nutrients form a rich area for bait and create good conditions for the bait and young fish. The fish spawning in the harbor was like 6-8m near the reef, and the trend was relatively stable. However, there was talk of water rushing in. The salinity was low (20.7-23.3‰) and sheltered from the shallows of the inner bay at Xiangwan. . The surface water temperature during spawning is 13-18°C and the pH is 8.0-8.2. According to a survey conducted by the Hebei Fisheries Research Institute in the spawning grounds in the Bohai Bay area, the important environmental conditions for the spawning of barracuda are as follows: water depth 1-10m, centered around 6m, muddy or slime, and surface temperature 18-1. At 22°C, the salinity is 27.0-30.3 ‰. The pH was 8.04 to 8,30 and the transparency was 0, 27 to 1.0 m. The surface water temperature and salinity were both higher than those in Xiangshan Port. Tide is an ecological factor that causes the spawning of barracudas. The first batch of spawning of barracuda is during the tidal wave (back tide). At this time, the spawning individuals are more concentrated and therefore present a peak. Spawning occurs during the day and night in the sea area. The spawning of P. ostreatus was carried out at 3 to 4 o'clock before dawn. A common group of barracudas chase each other before spawning, and one female fish is often followed by 3 to 4 males (up to 9). Spawning fish groups sometimes lean their abdomen against the mudflats on the bottom of the sea (Yangshan Harbor fishermen use pull-fishing to catch spawning broodstock during the breeding season), sometimes jumping into the water and diving into the water. This kind of intense action is a frictional stimulus. The abdomen and reproductive organs promote sexual maturity and spawning. (d) Oocyte maturation, ovulation, spawning and overcooking, degeneration and absorption Oocyte maturation In the term artificial reproduction of fish, "mature" has two different concepts: the so-called "fish has matured" means that the oocytes in the ovary have grown large and the yolk is full, reaching the IV level. During the middle and later stages of the period (nuclear polarized to animal poles), stimulation of exogenous hormones can cause normal maturation and ovulation response, so it can be called "growth maturation"; another so-called "egg maturation" refers to the fourth The stage oocyte undergoes the first maturation (decrease) division under the action of an exogenous hormone, releasing the first polar body, freeing the follicular cell from being surrounded, and the egg becoming a free state in the ovarian cavity, within a certain time limit Normally combined with sperm, it is also known as "mature maturation" or "physiological maturation." The former mature biological significance lies in achieving the level of oxytocin production. The latter mature biological significance lies in the ability to fertilize. 2. The ovulation and oviposition of oocytes in the ovary end the stage IV developmental stage into the V stage, the fourth stage of the oocyte outer periphery of the follicle membrane (in this regard due to the physical effect of increasing egg volume, On the other hand, due to the chemical action of the enzyme, the tissue between the follicle membrane and the egg membrane is dissolved and absorbed) and falls into the cavity of the ovary and becomes free. This process is called ovulation. Under suitable environmental conditions, when the broodstock enters the climax, due to the enhancement of sexual activity and the corresponding contraction of the smooth muscle in the ovary, as well as the contraction of the abdominal muscles, the aggregated in the ovarian cavity is completely mature and free. The egg is produced outside the body through the reproductive hole. This process is called spawning. Under normal circumstances, maturation, ovulation and spawning are coordinated with each other. If the ovaries have degenerated, or the eggs are still immature, the temperature of the production water is too high or too low, and the hormone dose is too large, it can lead to maturation. The chaotic step of spawning causes the egg to swell and cause dystocia. The genus Pseudacus is a mature type of ovum. 3. Over-ripening, degeneration, and absorption of eggs (1) The concept of over-ripening: Over-cooking includes both the "overgrowth" of the egg (over-ripening of the ovary) and the "physiological over-ripening" of the egg (over-ripening of the egg). Over-ripening of the ovary: When the ovary develops to the end of the fourth phase, the primary oocyte has grown and matured, and after quitting the dormant state, it waits for conditions to mature and divide. In this waiting time, oxytocin production, ovarian response to oxytocin is the most sensitive, and oxytocin is the most effective, and it is suitable for oxytocin production. If this period is appropriate, the sensitivity of the ovaries to oxytoctics is gradually reduced, and the egg cells begin to degenerate within the ovary and transfer to the stage of being absorbed. At this time, oxytocin rarely has a good effect. If it is too overdone, spawning is still Normal, but the egg membrane is soft, abnormal embryonic development. Over-ripe, but also spawning, but the egg membrane is softer, more deformed, and sometimes the embryo quickly decomposed, leaving only the milky white egg membrane, known as the "hollow egg." When the over-ripening is severe, the eggs cannot be produced. This over-ripening refers to the phenomenon that the gonads are out of date due to the delay of oxytocin production, that is, the so-called "over-ripening of the ovaries" or "overgrowth of the eggs". The over-ripening of eggs means that the eggs that have been discharged from the follicles lose their ability to be fertilized because they are not produced in time outside the body. The secondary oocyte that is in the middle of the second maturation split can receive sperm for a period of up to several hours, but the optimal time is only about 2 hours. Outside this optimum time, the embryo is barely fertilized. Most of the development is deformed or even disintegrated. If it is further from this period, it cannot be fertilized. Therefore, the proper maturation time of the egg within 2 hours after the middle metaphase is when the egg can be called "mature egg", and not called "immature egg" at this time. If it exceeds this time, it is Cooked eggs." (2) Degradation and Absorption of Overcooked Eggs: After spawning of females, a large number of ruptured follicles, oogonia, primary oocytes, and some unfamiliar, oversized secondary oocytes are left behind by the ovaries. . All of these, except oocyte, have been degraded and absorbed. Absorption of non-discharged overcooked eggs mainly depends on the function of follicular epithelial cells and absorption of young oocytes. Since the follicular membrane in the periphery of these oocytes has not yet formed, they are in some macrophages. Phagocytosis is absorbed, and the ruptured follicles after ovulation gradually expand into spongy in the ovary. Soon after its composition has undergone sexual changes and decomposition, the decomposed substance is absorbed into the blood. As the degenerated eggs are absorbed, the ovaries gradually contract. At the end of the absorption, the gonads return to phase II. (E) Embryonic development of barracudas in embryonic development. (1) Changes in fertilized eggs after water: According to the observation of Su Bingren et al. (1978), after fertilized eggs enter the water, the egg membrane expands and gradually rises from the egg surface. At the same time, the egg itself emits some substances and shrinks slightly, so that the egg membrane (also known as the fertilized membrane) and the surface of the egg form an interosseous gap. The perivitelline gap is narrow and its width is 0.015 to 0,020 mm. At this time, it can be seen that the fertilized egg is a crystal clear and lively ball. From the periphery to the center, the boundaries of the layers of the egg membrane, perivitelline space, eggs, and oil balls can be clearly separated. When the barracuda eggs are fertilized, the substances in the eggs have intense movement, and the eggs are even and light in color, so the cytoplasm flow is not noticeable. However, shortly after fertilization, it was the strong evidence that the cytoplasm was extremely fluid toward the animal, as the animal gradually rose up to form a blastoderm. After the epidemic appeared, the proportion of eggs in different parts of the egg had changed. There was a large oil ball in the middle of the egg, and there was a blastoderm in the animal. The proportion of the former was smaller, and the latter was larger. Therefore, when the egg floats naturally in the water, the oil globules are in the upper part and the blastoderm is in the lower part, and the embryonic body developed from the blastoderm is suspended below the egg. (2) Cleavage: Splitting of the barracuda fertilized egg, like other bony fish, is a discoidal cleavage. According to observations by Su Bingren et al., the water temperature was between 16.8 and 22°C. After the egg was fertilized for 1 h 15 min, it began to divide for the first time and the blastoderm was split into 2 cells of equal size. After another 30 min, a second division was performed. The divisional division of this division intersected with the first at right angles. As a result of division, 4 cells were formed on the blastoderm. The third divisional sulcus was parallel to the first one. As a result of the division, 8 cells were formed and arranged in two rows on the blastoderm with 4 cells in each row. The fourth divisional sulcus is parallel to the second one and forms 16 cells after division. Arranged in four columns with four columns. Three hours and 25 minutes after fertilization, the fifth division begins, 32 cells are formed on the blastoderm, and the sixth and seventh divisions successively continue. The number of cells continues to increase, and the volume gradually decreases. Become multi-cell stage. Since then, the more cells there are. (3) Blastocyst formation: Blastocysts are formed approximately 6 h after fertilization, and the blastoderm resembles a plate covered on the yolk. Thus, the disk-shaped blastocyst is defined as having a cavity between the central part of the blastocyst and the yolk, which is called a blastocyst. Cavity. (4) Gastrointestinal formation: Blastocyst cells were packaged from the periphery to the plant at around 10h after fertilization. During the process of subcontracting, due to the presence of yolk, the edge cells of the mineral exhibition were blocked and involuted. As a result, a folded cell layer gradually forms on the periphery of the blastoderm, thereby forming an embryonic ring. At this time, the embryo develops into the primitive bowel stage. During the gastrointestinal phase, substances that will form various organs on the blastocyst surface are moved to a certain position in the embryonic cavity by means of undercoating, involution, concentration, and stretching, and differentiation of the three germ layers is performed. The development of each part of the embryo is not uniform, of which the back lip part of the involution is the most significant, where the cells concentrate thickening to form the embryo shield. (5) Embryonic body formation, embryonic body is developed from the embryo shield. After 1/2 of the yolk of the blastoderm, the original mouth (embryonal hole) formed around the embryonic ring gradually became apparent. The embryonic ring continues to advance toward the plant pole, and the original mouth gradually shrinks. When the original mouth is close to close, most of the yolk is enveloped, leaving only a small group exposed outside the original mouth, called the yolk plug. While the embryonic ring advances toward the plant pole, the embryo shield continuously stretches into a tongue-and-groove structure. There is a thickening of the ectodermal cell line in the center of the embryo shield, extending from the base of the embryo shield to the front edge. This is the nerve cord. Below the nerve cord is the notochord, the mesoderm has differentiated on both sides of the notochord, and the outline of the embryonic body is gradually clear. About 24 hours after fertilization, the original mouth is closed, and the yolk plugs are all encapsulated in human embryos. Elongated embryonic body has reached the ovule sac for half an week. The neural tube in the front part of the embryonic body expands to form a brain and forms on both sides of the forebrain. Eye blisters. In the mesoderm on both sides of the notochord in the mid-embryonic body, the first 3 pairs of sarcomere were differentiated. After 6-7 hours, the sarcomere increased to 12-14 pairs. Tail buds appear to be uplift, the length of the head and tail of the embryo body has exceeded the half of the egg, the eyeballs on both sides of the forebrain are more pronounced, and the auditory plate is formed on the outer germ layers on both sides of the hindbrain. About 36 hours after fertilization, the sarcomere increased to 17-29 pairs. It was close to the yolk sac below the head of the embryo and the heart primordium was visible. Embryonic body tail has been extended from the yolk sac, pigment distribution along the embryonic body, in the interbody sulcus, there is a symmetrical phenomenon, a small amount of pigment on the yolk sac. After 42-43h after fertilization, the sarcomere has reached 26-28 pairs. The eye blisters have retracted into eye cups and have a crystal break. The capsule has formed. And can see the otolith. The heart can also beat, reaching 72-74 times per minute, and the embryo body twists in the egg membrane. Near the egg-out membrane, more than 30 pairs of sarcomeres were formed, and the tail of the embryo body wrap around the yolk sac, and the tail tip extended to the vicinity of the head. (6) Hatching: During hatching, the embryo body is frequently twisted in the membrane, and the tail continuously whips the egg membrane. Soon, the tail first protrudes out of the membrane, and then several shakes, and the whole embryo body flies out of the membrane. At the above water temperature, the whole process of embryonic development was completed within 48 hours and entered the life cycle of larvae. (VI) Biological characteristics of larvae, juveniles, and juveniles The developmental stage of fry has great changes in its morphological structure, living habits, and feeding habits. Generally, it is divided into three stages, namely: larval stage (including the former larval stage and post-larval stage). ), juvenile period and juvenile period. According to the study of Lei Lanlin et al. (1965), the morphological characteristics and living habits of barracuda fry at various water temperatures of 20-23°C are as follows: During the first larval stage, the yolk sac disappeared from the ruptured membrane. About 1-7 days, a total length of 1.94-4.30mm. The newly hatched larvae head tilted on the yolk sac and lived floating. On the 4th to the 5th day, the lids appeared, the membranes broke, the diameter of the mouth was 0.19-0.20mm, and the digestive tract had only esophagus, intestine, and rectum. After 5-6 days, the pectoral fins expand and begin to swim horizontally. At this time, they can turn to light and start feeding. To 6-7 days, the yolk sac completely disappeared. 2. After the larval stage disappeared from the yolk sac to the basic formation of the organ of movement, about 8 to 20 days after hatching, the length was 4.40-13.80 mm, and the upper and lower jaws were formed. The diameter of the mouth was more than 0.40 mm. The pectoral fins expand and other fins gradually form. The caudal fin changes from a circle to a square, and then begins to branch off. During this period, the larvae mostly move in the surface and in the middle of the water. In a larvae with a total length of 5 mm, a primordial primordium was found on the first arch. About 10 mm of larvae form a comb-like pupa with a palpitate spacing of 0.40 mm. At this time, the second pair of intestinal ridge and pyloric caecum primordium has differentiated in the stomach. 3. The juvenile stage develops well from each organ and scales begin to form before the body is weighed. About 21-30 days after hatching, the total length is 14.00-30.00mm. The diameter of the mouth is more than 0.80mm, scales gradually formed.鳃耙 鳃耙 denser, intestinal ridge increased to 3 to 5 pairs, caudal fin bifurcation stereotypes. Gradually turn into the bottom of the pool activities, then juvenile fish outside the basic shape is basically similar to the adult fish, but the color of the back-belly body is less than gray and clear. 4. Juvenile period begins with the whole body. About 30-48 days after hatching, the total length is 31-50mm, body shape and color are similar to adult fish, mouth diameter is 1.90-2.90mm, mouth split level is lower, with deep kiss pleats, can make mouth Department stretches forward. The inner wall of the pylorus stomach was developed. There were 5 pyloric caeca at the junction of the duodenal base and the pyloric stomach, and the intestinal fistula increased to more than 5 pairs. The ruthenium forms a dense mesh structure. Completely camp benthic life. As the individual grows, barracuda has a transformation process from simple to complex. That is to say, animal-like behavior and plant-extractability of all animals are mainly plant-based. From hatching to opening, relying on the body's yolk nutrition, known as the internal nutrition stage. After 5-7 days of incubation, the fry migrated and started to feed. At this time, the fry gradually changed from internal to external nutrition. This stage of transformation became a mixed nutrition stage. After about 8 days of hatching, the yolk sac of the fry disappeared and the nutrient of the ingested water was used as a nutrient. Since then, the external nutrition phase began. When fish fry open their mouths, they mainly ingest small zooplankton such as rotifers, copepods, nauplii and eggs. As the fry grows up, the mouth crack widens, and large copepods, horns, and Artemia larvae can be ingested. To a full length of 10 - 14mm, the initial formation of pupa and filter food, the number of phytoplankton intake increased significantly, accounting for more than 70% of the total food individuals. Phytoplankton is mainly composed of dinophytes such as dinoflagellates and Peridinum sp., and others are Platymonas sp. The juveniles with a total length of 14-30 mm, due to the lengthening of the digestive tract and the growth of the cockroaches, become a filter structure, and the proportion of ingested phytoplankton is as high as more than 90%, but it is still a mixture of animals and plants, and has greater plasticity. The juveniles with a total length of 31-50mm are mainly based on sedimentary phytoplankton and organic matter on the sediment.
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