The demand for water environment from marine fish culture

Fish live in water. Regardless of fresh water or seawater, the aquatic environment affects the growth and reproduction of fish and affects the physiology and ecological balance of fish. There are various variable factors in the aquatic environment if these variables exceed the limits of the fish body. Tolerable limits can cause fish diseases or endanger their survival. The physical and chemical factors of the ocean, such as temperature, salinity, pH, dissolved oxygen, water flow, and water pressure, etc. Understanding the changing patterns of these factors is a scientific basis for aquaculture production. (I) Water temperature fishes are variable-temperature animals whose body temperature changes with changes in the surrounding water temperature. The body temperature of most fishes differs from the surrounding water temperature by about 0.1 to 1°C. All kinds of fish have their heat-resistant upper and lower limits and the optimum temperature. Within the optimum temperature range, the fish eats, breathes, and digestive functions are vigorous, metabolism is enhanced, and growth is rapid. Exceeding the appropriate temperature range can cause metabolic disorders, growth inhibition, and even death. According to the fish's adaptability to temperature, it can be divided into tropical fish, warm water fish and cold water fish. Tropical fish are suitable for higher water temperature (25~30°C), but they are not tolerant to low temperature, and it is difficult to survive below 15~30°C. Groupers inhabit many sea otters in tropical and temperate sediments. The optimum temperature is 24~30°C, but there are differences among groupers. For example, the upper limit of LD50 for grouper is 38.5 ~ 39.5 °C, the lower limit is 11.5 ~ 13.0 °C. The optimum temperature for red-spotted groupers is 22 to 28.5°C. If the water temperature exceeds 32°C, the balance will be lost. The red-spotted grouper will easily die at 32.2°C. 32 °C is the upper limit of these groupers, the lower limit is 15 °C, 15 °C when the fish out of balance, stop feeding, inactivity, the water temperature dropped to 14 °C, the weak and spots with stripe easy to die, especially Thailand and The spotted macules produced in the Philippines are not resistant to low temperatures. (II) The dissolved salts in salinity water vary according to the water body, and the classification criteria are also inconsistent. Normally, 31 to 41 盐 salinity water is called seawater or alkaline water, and ∠0.5 ‰ water is fresh water. Fishes have certain physiological mechanisms for regulating the salinity of different degrees of salamanders, but they are limited to a certain range. Exceeding this range can affect their survival. According to the fish's ability to adapt to changes in salinity, it can be divided into two categories: wide salinity and narrow salinity, and red-spotted rock-spot, black-spot, etc. belong to wide-salinity fish, and the tolerance to salinity changes greatly. Groupers live in shallow harbour bays, and salinity can be adapted from 11 to 41 ft. c) The amount of dissolved oxygen in the dissolved oxygen environment directly affects the growth of farmed fish, food conversion, and the aquaculture capacity of the farm. Most fish do not directly absorb oxygen from the atmosphere, but are adapted to use helium to absorb dissolved oxygen in the water for gas exchange. The amount of dissolved oxygen in seawater is related to water temperature and salinity. The rate of oxygen in the atmosphere is generally inversely proportional to water temperature and salinity and is proportional to atmospheric pressure. Seawater generally contains saturated dissolved oxygen, and fish do not suffer from oxygen deprivation. However, under certain local conditions, anoxic conditions may also occur in the water layer. For example, when fish floats are too dense, water flow is poor, or stagnation (flat tide) occurs, the weather Sweltering, cloudy clouds or thunderstorms before the cage hole was blocked by attachments, stocking density is high, it may cause a lack of oxygen in the culture area. The aging of the site and the deposition of organic substances on the bottom can also cause oxygen deficiency in the bottom layer, causing the death of benthic animals and bottom fish. In general, when the amount of dissolved oxygen was 3 mg/l, the food intake of fish decreased, and when 2 mg/l was stopped, feeding was stopped. Breathing difficulties, fish floating heads or vomiting were observed. Adequate oxygen levels are necessary for fish life. During the aquaculture production process, the amount of dissolved oxygen in the waters inside and outside the cages should always be taken into account. If the fish are in a state of low oxygen for a long time, there will be less food intake, lower metabolic rate, and life function. Reduced, dissolved oxygen should be maintained at 4 mg/l or more. Yellowstone spot 0.8468mg/L floating head. d) Hydrogen Ion Concentration The hydrogen ion concentration of water, the pH of the water, is expressed in terms of pH and is divided into 14 levels. [H+] concentration is 100 nanomol/liter (nml/L) = pH7 is neutral, [H*] Concentrations greater than 100 nanomoles/liter, ie, pHs less than 7 are acidic, and [H+] concentrations are less than 100 nanomoles/liter, ie, pH 7 is more than 7 is alkaline. The change of PH value is affected by the water quality factors such as carbon dioxide, dissolved oxygen, dissolved salts and salinity, mainly due to the ratio of free carbon dioxide, carbonate, and bicarbonate in the water. Generally, the more carbon dioxide, the higher the pH value. The lower, on the contrary, the lower the carbon dioxide, the higher the pH. Hydrogen ion concentration has a very important impact on water quality, aquatic animals and plants. All kinds of fish have their optimum pH range, most fish adapt to a pH range of 7.0 to 8.5, favoring a weak alkaline environment, grouper The suitable range of pH value for fish is 6.8-8.0. A pH of less than 5 or greater than 9.5 causes the fish to die. Acidic water can make the pH value of fish's blood drop [H+] increase), which makes the combination of hemoglobin and oxygen obstructed, reduces the oxygen carrying capacity of blood cell, and causes the partial pressure of oxygen in the blood to become smaller, even if the content in the surrounding water is still high, As a result, fish also suffer from hypoxia, which reduces their metabolic function and inhibits their growth. Therefore, long-term in acidic water, the fish can be weakened, or easy to infect and cause detoxification. Seawater is one of the best buffers for the variation of hydrogen concentration. The final polluted seawater has a pH of 7.85~8.35, which is suitable for fish growth and development. (v) Flowing seawater fish farms shall remove harmful ammonia, such as ammonia-nitrogen (NH3-N) accumulated in cages, and accumulations at the bottom of cages and detrimental hydrogen sulfide (H3S), etc., in order to maintain good water quality. For gas, breeding sites should maintain adequate flow or flow of water from the coast flow into and out of the cages and rinse the rows of fish in order to ensure high dissolved oxygen levels in the cages. This is a case of high-density intensive cage fish culture. It's crucial. If the tide or the coast is strong, it is not appropriate because the fish have to consume a lot of energy to maintain their stability and affect the growth rate of the fish. It is generally believed that the proper flow rate for the floating cage culture of the Gulf is: inside the cage. For 0.1 to 0.2 m/s, the flow rate outside the cage is 0.3 to 0.5 m/s. The amount of dissolved oxygen in cages with cage meshes between 7.5 and 50.5 mm is above 50% saturation. Sink-type cage culture requires a higher Zhu flow rate, preferably between 0.75 and 1.0 m/s, suitable for large-scale cage culture of fast-flowing marine fish. Poor water exchange is not suitable for cage culture, because it does not meet the basic requirements of intensive culture, limiting the stocking density per unit of water surface and water self-purification. The total amount of biomass that can be borne by a specific area depends on the exchange of water flow. When the tide is small, the exchange of water flow is limited and it is difficult to conduct high density intensive culture. In the case of increased number of attachments to the net and blocked meshes, the flow rate in the net decreases, and the amount of exchange decreases. In order to maintain a sufficient amount of dissolved oxygen in the tank, it is often necessary to periodically clean the cage. (6) Hydraulic pressure refers to the pressure (P) at one point in the ocean, that is, the static pressure at a certain depth, which can be represented by the force of the water column acting on a square area of ​​1 square centimeter. The weight of the water column per unit area is equal to the product of seawater depth (h), seawater density (p) and gravitational acceleration (g), ie P=pgh (units): dyne/cm2 or bar). 1 bar = 106 dynes/cm2, set at 1 bar per square centimeter when the pressure is 1 million dyne. Oceanography often uses the debit as a practical unit, that is, 1 bar = 1/10 = 105 dyne/cm2. For each additional water depth of 1 meter, the pressure is usually increased by 1 bar. For every 10 meters of water depth, the pressure increases by one atmosphere. In 100 meters of deep water, the pressure in the urn is about 10 atmospheres. At 2,000 meters depth, fish were found to be gas-filled. There were 200 atmospheric pressures in the urn. When the fish enter the deeper layer from the shallow layer, gas traps need to add gas to maintain neutral buoyancy. The fish in the deep sea have long-term inhabitation under great pressure. The bones are thin and loose and flexible. The bones and bones are also loose and easy to separate. The muscles on both sides of the fish are underdeveloped, and the mouth is large and the stomach is stretched. Strong, many dissolved gases in the intestines and blood, so when caught in the water, the pressure plummeted and the gas swelled, often causing the muscle blood vessels to rupture. The viscera turned over and the eyeball protruded from the eyelids and died. Marine organisms have adaptability to certain water pressures. Living in high water pressure fish does not easily survive at low water pressures. Similarly, living in low water pressure fish is not suitable for survival at high water pressures. When deep-water fish catches rises sharply, the water layer changes quickly, and fish do not have enough time to exhaust. When the fish reaches the surface, the gas pressure of the human body greatly exceeds the surface water pressure and the pressure in the air. The pressure suddenly decreases the swelling of the fish and can expand the body cavity. The stomach in the outside of the mouth, such as croaker caught in deep water, can happen. Groupers are caught in deep water (above 8 meters in depth). As the pressure drops sharply, insufflation of the inflated abdomen can also occur. Fishermen generally use bamboo needles or injection needles to deflate and raise them. This type of fish has trauma. It is not appropriate to do long-distance sales immediately.

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