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Wen 丨 Yujie History Museum
Editor丨Yujie History Museum
Grass carp, commonly known as grass carp, belongs to the teleost fish, cyprinids, cyprinidae, Yaro fish subfamily, grass carp genus, and blue carp, silver carp, bighead carp and known as the world-famous "four big fish".
Grass carp has been widely transplanted around the world in recent years because of its rapid growth, large and tender body, rich nutrition, and wide range of feed sources.
Grass carp is an important freshwater farmed fish in mainland China, with fast growth, relatively low feed protein demand and other characteristics, with the development of intensive aquaculture mode, grass carp aquaculture industry has been rapidly developed, aquaculture production has been improved.
However, due to the increase in stocking density, rising temperature, drug abuse and inappropriate feeding strategies and management methods, the breeding environment has deteriorated, the disease resistance of farmed animals has decreased, and the breeding efficiency has declined.
Therefore, the realization of large-scale, high-density, high-quality pond intensive aquaculture, as well as controllable diseases such as disease, feed, water quality and other aquaculture-related factors, is of great practical significance to mitigate or avoid the negative impact of environmental stress on fish farming.
Next, let's take a look at Yujie: in the process of raising grass carp, what is the impact of the change of breeding density and temperature on its growth and physiological indicators?
Effects of culture density on grass carp growth
Environmental stress is an important consideration when farming fish, including temperature rises and falls, dissolved oxygen levels and congestion stress due to high farming densities.
In particular, crowding stress is often a significant factor in the process of intensive aquaculture, which can trigger the stress response of fish, trigger changes in physiological processes such as growth, feeding, behavior, energy metabolism, etc., change the internal physiological state of fish, weaken the body's disease resistance, and also lead to the expansion of growth differences between individuals.
Most studies have shown that high-density farming significantly inhibits individual fish growth. Regarding the impact of farming density on fish, there have been a large number of foreign research reports, covering growth, reproduction, blood physiology, immunity and other aspects.
The effects of crowding stress on the non-specific immune function of grass carp, the effects of culture density on feeding, growth and behavior of sturgeon sturgeon, and the effects of chronic crowding stress on carp growth and blood biochemical indexes.
Studying the influence of aquaculture density on fish growth and physiology is of great significance for in-depth understanding of fish stress and stress mechanism, exploring reasonable aquaculture management mode, and improving the economic benefits of aquaculture.
Therefore, different breeding densities were set, feeding under different treatment conditions, and physiological indicators such as growth, survival, organ coefficient and other physiological indicators were measured, and biochemical parameters such as antioxidant enzymes were also detected to analyze the effect of density on the growth of grass carp and reveal its physiological mechanism.
This will help to provide practical guidance for the rational development of culture density and culture patterns, thereby improving the economic efficiency of the aquaculture industry.
So what other impact does the difference in farming density have on grass carp?
Effect of culture density on the immune system of grass carp
At high farming densities, fish experience a stress response, which is a protective, adaptive physiological response, and if fish continue to be stressed, their immune defense function will be inhibited, resulting in fish becoming more sensitive to various pathogens, prone to various diseases, and eventually leading to death.
The core of this stress mechanism is that long-term stress by environmental factors leads to the release of large amounts of corticosteroids in mammals, which may inhibit the normal function of the immune system while causing varying degrees of damage to immune cells, tissues and organs.
The results showed that after a period of culture, the liver system number of grass carp in each density group showed an increasing trend, although the effect of density on the liver system number of grass carp was not significant, but the culture duration had a significant effect on it.
With the extension of rearing time, the liver system number of grass carp continued to increase, and there were significant differences in the liver system number in different time periods.
This shows that under the current culture environment, the density groups do not pose a significant threat to the survival and growth of grass carp.
Unlike previous studies, the results on the decrease in liver body index in the high-density group were inconsistent, which may be related to factors such as experimental conditions, breeding equipment, manual operation and feed feeding.
Good water quality conditions may help to mitigate the effect of density on grass carp during the experiment.
When a certain density was found, the number of spleen systems of grass carp reached the maximum, which indicated that grass carp in each density group began to gradually adapt to the breeding environment after a period of culture, and its physiological and immune functions tended to be stable.
The number of spleens then drops to its lowest value, which may mean that environmental stress is beginning to affect its survival, which is significantly different from the other groups.
This is inconsistent with the results of some other studies, which may be related to factors such as the size of the grass carp, the cyclability of the water flow in the breeding pond, the surrounding environment and manual operation errors.
The number of spleen systems in each group began to rise and basically returned to the initial state, which may indicate that after a period of environmental adaptation, the spleen function of the fish body gradually recovered and the physiological function tended to be stable.
The number of spleen systems in the high-density group has been stable, basically unchanged, and in some periods of time it is higher than that of the low-density group, which may be because the breeding circulatory system provides good water quality conditions and sufficient dissolved oxygen during the experiment, thereby alleviating the impact of high density on the immune system of grass carp.
So, what is the effect of culture density on the enzyme activity of grass carp?
Effect of culture density on enzyme activity of grass carp
SOD enzymes and CAT enzymes play a key role in the body's antioxidant system, effectively scavenging reactive oxygen radicals and preventing peroxidation.
SOD enzymes are responsible for scavenging superoxide anion radicals, catalyzing their production into H2O2, while CAT enzymes break down and scavenge hydrogen oxygen radicals produced by cells, converting them into harmless H2O and O2.
These two enzymes usually work synergistically to remove reactive oxygen radicals from the body to avoid damage to the body.
Under mild environmental stress, the activity of SOD and CAT usually rises to remove reactive oxygen radicals in the body, and under long-term and intense adversity, large amounts of reactive oxygen radicals accumulate in the body.
This in turn exceeds the processing capacity of the antioxidant defense system, resulting in a decrease in the activity of SOD and CAT, which ultimately reduces the viability of the body.
In the conventional density group, SOD and CAT enzyme activities in the liver of grass carp were basically stable throughout the culture process, which indicated that under this density condition, the environment was relatively stable, and the density factor had no obvious effect on grass carp, which could be used as a control group.
Compared with the conventional density group, the SOD activity of grass carp in the liver reached a maximum after 7 days of rearing, and was significantly higher than that of the conventional density group.
Subsequently, their activity began to decline and gradually stabilized, and the activity trend of CAT enzymes was similar to that of SOD enzymes.
The trend of SOD and CAT showed that when the culture density increased from the acclimation density (2.3 g/L) to the initial experimental density, the interaction between individuals increased due to the increase in density.
Increased stress, which leads to the accumulation of reactive oxygen radicals in the body, and increased activity of SOD and CAT helps the body's antioxidant defense system to remove these free radicals.
This is consistent with the rapid increase in cortisol levels in the body after increasing density.
SOD and CAT activities in grass carp liver are time-dependent at different densities. After 14 days of rearing, their activity begins to decline. Combined with the growth results at different densities, the reasons for the decline of SOD and CAT after 14 days of rearing may vary.
At low density (5g/L), grass carp gradually adapted to the change of density after 14 days of rearing, and the physiological state tended to be stable, and the influence of the external environment gradually decreased.
It was not until 60 days that the body's defense system returned to its original state, enzyme activity decreased to a stable level, and the low-density group showed the highest rate of specific growth within 60 days after the end of the test.
Under medium density and high density, with the extension of the breeding time, the breeding environment faced by grass carp of different density groups becomes more harsh, which is seriously affected by environmental stress, resulting in the body producing a large number of reactive oxygen radicals.
This outweighs the antioxidant defense system's ability to scavenge these free radicals, ultimately resulting in inhibited enzyme activity and therefore a lower growth rate than the grass carp group at low densities.
The above observations show that the culture density has a significant impact on the physiological state and antioxidant capacity of grass carp. There are differences in stress response and growth performance of grass carp at different densities, which provides an important reference for the optimization of grass carp culture density.
The experimental results showed that different culture densities had a significant impact on the growth and physiological indexes of grass carp, high-density culture could inhibit the individual growth of grass carp, while the low-density group showed a higher specific growth rate after the adaptation period.
The culture density also affected the organ coefficient of grass carp, reflecting its adaptation to the breeding environment, and the immune system of grass carp at different densities was also affected to varying degrees, and the group with higher density was more susceptible to environmental stress, resulting in decreased immune function.
When the culture density increases, the activity of these two antioxidant enzymes in the liver of grass carp also increases significantly, thereby helping to scavenge reactive oxygen radicals in the body.
However, with the extension of the rearing period and the intensification of stress, the activity of these enzymes eventually decreased, indicating that the fish gradually adapted to environmental stress.
The effects of culture density on the growth, physiological state and antioxidant capacity of grass carp were further discussed, which provided a theoretical basis for the optimization of culture density and management mode.
By mitigating or avoiding the adverse effects of environmental stress on fish farming, we can better protect the sustainable development of aquaculture and ensure its socio-economic importance.