Some people think that when a fish is dead, there is no need to delve into the cause of its death or to distinguish the difference between the death of the fish, but in fact, there are many causes of fish death, such as fish disease, lack of oxygen, toxic algae poisoning, chemical poisoning, etc.
Although the fish has died, we should still conduct in-depth analysis and judgment of the dead fish and water bodies, and find out the real cause of the death of the fish according to the difference in the death of the fish, especially the poisoned dead fish caused by being poisoned or discharged by the factory, which is very helpful for the report to analyze the poisoner and the basis needed to claim from the factory.
Most importantly, summing up the lessons learned and accumulating experience can be of great benefit to future fish farming production, which is the so-called 'it is not too late to make up for the lost sheep'.
First, the characteristics of dead fish poisoned by chemicals
1. Death from acute poisoning of fish chemicals. Due to the discharge (inlet) of toxic chemicals into fishery waters, resulting in a high concentration and height of water body poisons, this dead fish has a strong suddenness, without any warning, the fish will die in large numbers in a short period of time, and the mortality rate is very high.
2. Differentiation. Different species of fish have different resistance to the same poison, that is, their semi-lethal concentrations are different, for the same poison, fish with low semi-lethal concentrations are more likely to die than fish with high semi-lethal concentrations, that is, die earlier, faster, more, therefore, there is a certain variety selectivity, but in the toxicity is very strong, the toxic concentration is very high, all kinds of fish will die quickly, the selectivity of the variety is not very obvious.
3. Chemical poisoning of dead fish may occur all year round and at every moment. It has little to do with temperature and water temperature, but with the time when toxic chemicals are discharged into fishery waters, so the time and season of occurrence are uncertain.
4. Selectivity. Fish of the same species, individual small young fish, especially juvenile fish and juvenile fish, are sensitive to poisons than individual adult fish, poor resistance, so it is easy to die, manifested in chemical poisoning, small fish die before large fish, and the proportion of small fish death is higher than that of large fish, so it has obvious individual size selectivity.
5. At the beginning of poisoning, most poisons will cause fish to appear as jumping, charging, rolling up and down, swimming fast and other behaviors. In the later stages of poisoning, he showed weakness, lost his balance, died of death.
6. Specificity. When the chemical is poisoned, the morphology of the fish changes, and some have a certain specificity.
When heavy metal poisoning, the gills of the fish are damaged more obviously, the skin cells are destroyed, and even the gill leaves are partially shed, and the gills secrete a large amount of mucus to form a flocculent heap.
Yellow phosphorus poisoning is the fish's eyeballs protruding and the scales erect. Cyanide poisoning is bright red in gills. Residual chlorine poisoning is body color, gill filaments are white.
Alkal poisoning is a large amount of mucus on the surface of the fish.
7. When fish die of acute poisoning due to chemicals, other organisms in the water, such as plants, turtles, snakes, frogs and snails in the water, will also die of poisoning. The number and breed of zooplankton in the water will be greatly reduced or even disappeared.
Heavy metal poisoning can reduce the number of phytoplankton species in the water, and there will be a large number of dead algae cells in the water.
Algae killers can kill almost all algae in the water.
8. Poisoned dead fish is caused by the water environment caused by the discharge of chemicals into the fishery water body. Generally speaking, the area of this pollution is limited, and the area of serious pollution is even more limited, so the chemical poisoning of dead fish is within a limited range, it occurs in isolation, and it does not have universality and epidemic.
9. Chemical poisoning often causes some pollutants to be attached to the gills of fish, especially the gills of fish, and often carries the unique odor of those substances. Such as oil, yellow phosphorus, pesticides, etc. will be attached to the fish body and gills, and have an odor.
10. Generally speaking, the dissolved oxygen, PH value, water odor and water color changes of the water poisoned by chemicals are different depending on the chemical. Acid, alkali pollutants dead fish will change the PH value, pesticide pollution of dead fish, water often have the smell of pesticides, the above indicators are difficult to give a certain characteristic, depending on the specific situation.
11. Put an appropriate amount of water of the water body of the dead fish in the aquarium or other clean containers and healthy fish of the same species and size as the dead fish for lethal experiments. If the experiment has an acute poisoning phenomenon or an acute death that is significantly different from the control group, the diagnosis of dead fish with acute chemical poisoning is critical, but the dilution, decomposition, precipitation, etc. of the poison will make this indicator unable to reflect the real situation, so timely sampling and testing are very necessary.
Second, the difference between dead fish with fish disease and dead fish poisoned by chemicals
1. There are two kinds of occurrence and death of fish diseases: acute and chronic.
Acute fish diseases onset is very fast, the precursors are not obvious, once the onset will be a large number of deaths in a short period of time, explosive fish diseases belong to this category.
In acute fish disease, the behavior of the fish before death is difficult to see a clear difference from the behavior of normal fish, which looks normal in behavior, but will suddenly die in large numbers.
This is different from the collision, tumbling and jumping performance of fish when the chemical is acutely poisoned.
Chronic fish disease dead fish, its onset and death is relatively flat, from the onset of illness to death there is a process, the precursor is more obvious, many fish are gradually dying, will not occur in a short period of time a large number of deaths.
This is completely different from sudden death from acute poisoning of chemicals.
When fish are dead from chronic fish disease, the body of the fish is generally weak, there is no food in the stomach, the activity is slow, the group swims alone, and likes to move in the dark.
This is also completely different from the behavioral response of fish in the acute poisoning of chemicals.
Although some parasites (fish lice) diseases make fish jump and crash, they are relatively rare. And it will not cause the fish to die in large numbers in a short period of time.
2, many fish diseases have a certain degree of selectivity. For example, bleeding disease is mainly grass carp and blue fish, printing disease is mainly mainly bighead carp, tail stalk disease mainly occurs in eels and grass carp.
This is different from the high toxicity of acute poisoning of chemicals without obvious cultibility, even if the acute poisoning of dead fish has a certain variety selectivity, it is not the same as the species selected for fish diseases.
3. The season in which fish disease occurs generally begins in spring and is most prominent in summer. Because the water temperature and temperature are relatively high in summer, pathogens such as bacteria are easy to multiply.
This is not the same as chemical poisoning without seasonal restrictions.
4. Many fish diseases have their characteristic diseases. For example, grass carp hemorrhage disease, on the fish head, fins, internal organs bleeding significantly. The print disease has a circular or oval red mark on a certain part of the surface of the fish body. Iodine vesicle disease has a cell sac on the surface of the body. In case of explosive fish disease caused by hemolytic hydrophilic aeromonas, the fish's orbit, gill cap epidermis, body surface, fins, muscle congestion, ascites of the diseased fish, intestinal congestion, part of the intestine containing yellow mucus, liver and spleen congestion or necrosis.
There are many differences between the morphological changes of chemical poisoning and the morphological changes of fish diseases, but there are also some similarities, which should be carefully observed and analyzed.
5. Sick and dead fish. Attachments are generally absent on the surface of the body and gills, and some diseases can cause the gills of the fish to rot and have some putrid smell.
But this is clearly different from the attachments when the chemical is poisoned and its characteristic poisonous smell.
6. When fish disease and dead fish occur, generally speaking, the zooplankton, phytoplankton, aquatic plants and aquatic animals such as turtles, snakes, frogs, snails and other aquatic animals in the water will not be significantly damaged, and the number will not be significantly reduced.
This is completely different from the species in which acute poisoning of chemicals can cause a significant reduction in the number of deaths of other aquatic animals.
7. Bacterial and parasitic fish diseases. Pathogens can be detected on the surface, gills, internal organs, and blood of fish by visual or microscopic examination. For example, iodine vesperiasis takes the epicystle sac, a large number of iodolite spores are seen under the microscope, and the current epidemic of explosive fish disease can be taken from the dead cod liver, kidney and other internal organs to be observed by culture to hemolytic hydrophilic aeromonas.
This is impossible to observe on the body of a dead fish poisoned by chemicals, which is the biggest difference between the two.
8. Due to the infection of pathogens such as bacteria and viruses through water bodies, bait, seedlings and other links. As a result, fish diseases often have a tendency to occur in epidemics, that is, the same type of fish disease may occur on a considerable scale.
This is different from the limited range of chemical poisoning dead fish, which occurs in isolation.
9. The changes in dissolved oxygen, PH value, water color and odor of the fish disease and dead fish water body are not obvious. Water bodies may exhibit eutrophication, such as high levels of ammonia nitrogen and nitrite.
10, take the water of the diseased and dead fish, put in the healthy fish, bacterial, viral and parasitic diseases can not make these healthy fish in a short period of time and a large number of deaths. In general, it takes about a week for severe viruses and bacteria to cause fish to fall ill and die.
This is different from acute poisoning of chemicals, whether healthy fish or not, will have a toxic reaction.
Third, the difference between dead fish with toxic algae and dead fish poisoned by chemicals
1. Dead fish of toxic algae are caused by water poisoning algae. At present, the common poisonous algae that cause fish death in China are patina microcystis, splash microcystis, dinoflagellates, psilocybinoids, dancing golden algae, small trichoderm algae, etc. Due to the large number of these toxic algae varieties in the water to become dominant species, other algae varieties have been significantly reduced.
When chemicals poison dead fish, the number of algae varieties generally does not change significantly, although heavy metals and algae killers will reduce or even basically disappear the number of algae varieties, but there is no dominant species
2. Due to the large number of toxic dominant species. So that the light and action is enhanced, absorbing a large amount of carbon dioxide, so that the water PH increases, even up to PH>9, so the water will be easy to be alkaline, and these algae are suitable for survival and reproduction in the alkaline environment of the water body.
This is also a characteristic of the water quality of dead fish with poisonous algae.
3. Due to the enhancement of photosynthesis. Dissolved oxygen in the surface layer of water may be saturated and supersaturated, while the bottom layer may be in a state of hypoxia due to large amounts of oxygen consumption due to the death of algae.
This is also a very different point from the general chemical poisoning of dead fish when the dissolved oxygen of the whole water body is sometimes extremely low.
4, due to the difference in algae. The color of the water body is also different, the water bodies of Aeruginosa and Phylloscopus are copper-green, the water color of Dinoflagellus and Psilocystis is reddish brown, and the water color of Dancing Trichophyllum and The Water Color of Trichoderma is thick yellowish brown.
Fourth, the difference between dead fish with hypoxia and dead fish with chemical poisoning
1. Due to the different varieties of fish, the degree of low oxygen tolerance is different. Therefore, when the water body is not extremely hypoxic, some species of fish may die, some species of fish may survive, some species of fish have a higher proportion of death, and some have a lower proportion of death.
The selectivity of this variety is not necessarily the same as that of no variety poisoned by chemicals, of course, in the case of extreme hypoxia, all varieties will die, and the choice of this variety no longer exists.
2, in the aquaculture water body due to the bait more. Dead fish with hypoxia caused by large farming densities generally occur in late spring, early autumn and summer when the weather is hot and the air pressure is relatively low, often between 00:00 and before dawn, and there are few or no dead fish at other times.
This is different from the uncertain timing and season of occurrence of dead fish poisoned by chemicals.
3. When dead fish are deficient in oxygen. Fish with large individuals generally die first, and the proportion of deaths is higher than that of individual small fish.
This is the opposite of selectivity regardless of individual size when poisoned with chemicals.
4. When the water body is hypoxic, the fish is in a floating state. That is, the fish swallow the air on the surface of the water and swim along the pond wall.
It is completely different from the behavior of dead fish poisoned by chemicals such as collision and jumping.
5. The pectoral fin of the fish who dies of hypoxia is generally stretched to the front position, and the fin is white. The shape of the fish is different from the shape of the fish when the chemical poisoning dies.
In addition, fish that die of hypoxia generally do not observe the contaminated attachments that often occur in chemical poisoning on the surface and gills.
6. When dead fish are deficient in oxygen, other aquatic organisms such as aquatic weeds, turtles, snakes, frogs, snails and so on generally do not die.
This is significantly different from the fact that aquatic plants may change color when chemicals are poisoned, and other aquatic animals die in large numbers.
7. The most obvious water quality index of oxygen-starved dead fish is that the dissolved oxygen in the water is very low, which is generally lower than the fishery water quality standard.
This is the most obvious difference between the level of dissolved oxygen between dead fish with hypoxia and general chemical poisoning death.
8. When there is a lack of oxygen and dead fish, the water body often emits a sour cabbage smell, a musty taste and a foul smell, and the water color is often black and gray-white.
The smell and color of the water body when poisoning with chemicals varies according to the chemicals.
Reprint statement This article is transferred from [Splash Fish].