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Wen 丨 Yujie History Museum
Editor丨Yujie History Museum
Penus chinensis is one of the important farmed shrimp species in the mainland, its body color is bright, dry dew tolerant, so it can be sold live, the sales price is high, and the profit margin of breeding is large.
However, compared with other common farmed shrimp species, such as P. vannamei and Penaeus monodon, the culture technology of P. chinensis is not mature enough, and the aquaculture output is far lower than that of other common cultured shrimp species.
Aquaculture density is an important factor affecting the production of Japanese sac shrimp, and suitable culture density can not only make full use of the water body, but also reduce the probability of disease outbreaks due to environmental degradation in the process of Japanese sac shrimp.
Conversely, too high or too low a culture density not only does not effectively increase the production of farmed Japanese p. shrimp, but also increases the risk of farming and reduces the profitability of farming.
At the same time, biological floc technology has the advantages of stable water quality, supplementary food and increased production of farmed organisms in aquaculture, and has been widely used in aquaculture.
Next, let's follow Yujie to see: in the process of feeding Japanese capsule shrimp, the difference in breeding density can improve the growth performance of shrimp, and then improve the survival rate of juvenile shrimp.
Japanese p. sac shrimp farming
The shrimp industry has always been the pillar industry of the mainland aquaculture industry, since the shrimp industry suffered a major blow in 1993, the scale and output of shrimp aquaculture gradually recovered, and by 2002, the mainland shrimp aquaculture output ranked first in the world, reaching 320,000 tons, and its export volume and export value also reached a new high.
However, after 2006, the mainland shrimp industry faced more and more serious problems such as shrinking breeding area, diseases and environmental pollution, and the growth rate of shrimp production slowed down significantly.
From 2014 to 2016, the domestic shrimp production in the mainland showed a downward trend year by year, with 1.3 million tons, 900,000 tons and 800,000 tons respectively.
However, there is currently a large gap in demand for shrimp, with a demand of more than 1.7 million tons.
However, with the emergence of new technologies such as genetic breeding, disease prevention technology, and new breeding models, it has brought a new dawn to the development of the shrimp industry.
At present, the mainland shrimp aquaculture industry accounts for the vast majority of four kinds of shrimp: vannabin, Japanese capsule shrimp, monodon shrimp and Chinese prawn.
Under the conditions of indoor intensive culture, suitable culture density can not only make full use of the water body, but also reduce the probability of disease outbreak due to environmental degradation in the process of shrimp culture.
Conversely, too high or too low a farming density not only does not effectively increase shrimp production, but also increases farming risks and reduces farming profits.
Aquaculture density is an important aquaculture management factor, which mainly affects the growth, survival, feeding, physiological and biochemical level and behavior of shrimp by affecting the aquaculture water environment, the competition between food and living space, and population struggle.
At present, the effects of culture density on farmed organisms mainly focus on growth and survival, as well as the activity of stress-related enzymes in the body.
So based on this situation, how do we design experiments?
Design of experiments
Five culture groups with different density gradients were designed based on their initial mean body weight, body length, and cephalothorax length.
The five density gradients were: 20/m³, 40/m³, 80/m³, 130/m³, and 260/m³, each with three parallel control groups for a total of 15 ponds.
The focus is on exploring the effect of culture density on the cultivation of P. japo shrimp, including the following three outcomes:
The initial average body weight was 0.034±0.007 g, the initial average body length was 1.55±0.11 cm, and the initial average cephalothorax length was 0.42±0.065 cm.
The experiment was conducted based on the conditions of biological floc culture, and the effect of different culture densities on the culture of Japanese p. sacs was studied.
The results included the effects on the cultivation of P. japo shrimp at different density gradients.
Under the conditions of biological flocculation, the main water quality factors in the aquaculture water during the culture of P. sapped shrimp were kept within a suitable growth range.
Specifically, the temperature and pH of the aquaculture water of each aquaculture density group did not fluctuate significantly during the culture time, the temperature remained at about 28±1 °C, and the pH remained at 7.9±0.3.
Salinity decreases slightly during culture, reaching 25% at its lowest. This is mainly due to the occurrence of continuous precipitation at a certain period, which led to a slight decrease in the salinity of coastal seawater.
The overall change trend of ammonia nitrogen and nitrite during the breeding period was relatively consistent, rising first and then falling, and then remained relatively stable, with peaks of 0.30mg/L and 2.0mg/L, respectively.
In summary, the main water quality factors during the experiment were within the suitable living range of Penaeus sagigan, and there was no significant difference between different culture density groups (I>0.05).
So then again, what impact does the difference in farming density have on the growth of shrimp?
Effect of culture density on growth traits of P. chinensis
During the culture period, the growth traits of P. japonica, including body length, body weight and cephalothorax length, showed a gradual decrease with the increase of culture density, and this difference was significant (P < 0.01).
In addition, the culture density also significantly affected the survival rate and antennae fracture rate of P. japonica.
With the increase of culture density, the survival rate decreased significantly (P < 0.05). At the end of the experiment, the survival rates of Penaeus japo for each density group were 35% (E), 54% (D), 54% (O), 65% (B) and 85% (A), respectively.
With the increase of culture density, the antennae fracture rate also increased significantly (P < 0.05). At the end of the experiment, the antennae fracture rates of Penitus japonica for each culture density group were 76% (E), 74% (D), 53% (C), 12% (B) and 7% (A), respectively.
Heat shock proteins (HSP60, HSP70, HSP90): The relative expression of all three heat shock proteins increased significantly with the increase of initial culture density.
The expression of HSP in antennal fractured (D) individuals was significantly higher than that in antennae intact (W) individuals. In particular, the relative expression of HSP70 in Japanese capsule shrimp is large, and the difference in gene expression caused by antennae fracture is particularly significant.
Oxidative stress: The culture density had a significant effect on the expression of three oxidative stress-related genes in P. chinensis (P < 0.05).
Specifically, the expression of NADPH was upregulated with the increase of initial culture density, while in antennal fractured (D) individuals, the expression of NADPH was significantly higher than that in antennal-intact (W) individuals.
In addition, both SODs were regulated upward with increasing culture density in antennal fractured (D) individuals, but downregulated with increasing culture density in antennal intact (W) individuals.
Moreover, NADPH and SOD expression were at a relatively low level in the initial low-density group, indicating that low-density farmed Japanese sac shrimp were less stressed.
These results showed that culture density could significantly affect the expression of stress genes in P. sac, especially heat shock protein and oxidative stress-related genes, and there were obvious differences in the coping methods of P. v. vulgaris under different culture density conditions.
So in addition to the above, what other aspects should shrimp farming focus on?
Water quality monitoring
A suitable aquaculture water environment can promote the growth of shrimp and increase the yield of shrimp culture, on the contrary, the deterioration of the water environment is accompanied by slow growth and high mortality.
To judge whether the water environment is good, it is mainly judged by the physical and chemical properties of the water body and the content of dissolved substances.
Common water quality factors mainly include water temperature, salinity, pH, dissolved oxygen, ammonia nitrogen, nitrite, etc.
These water quality factors directly or indirectly affect the growth and immune status of farmed organisms, and are closely related to the success rate and efficiency of farming.
In actual production, some important water quality factors are usually monitored in real time to achieve timely water replacement and avoid the continuous deterioration of the breeding environment.
Breeding density is an important factor affecting aquaculture production and a prominent feature of factory farming.
Nowadays, several common farmed shrimp have basically realized factory farming, especially vannabin shrimp, and the culture density can reach high under indoor intensive culture conditions.
With the increase of breeding density, the utilization rate of water increases, followed by the intense consumption of dissolved oxygen in water and the accumulation of metabolic waste, such as manure and residual bait.
Under such conditions, it often causes the decline of dissolved oxygen in the aquaculture water and the accumulation of harmful substances, such as ammonia nitrogen and nitrite.
The culture density of P. vannamei has a direct impact on the water quality factors in the aquaculture water, and the higher the culture density, the more serious the deterioration of water quality.
The influence of breeding density on the growth, survival and stress of aquaculture organisms should be ruled out by the fluctuation of major water quality factors in the breeding process on the experimental results.
So, what impact will the change in shrimp farming density have on the growth of shrimp?
Effect of breeding density on growth index
The ultimate goal of aquaculture is to obtain a large number of individuals with large specifications in a relatively short period of time, in order to obtain higher breeding profits. When the food is sufficient and the water quality is excellent, although the aquaculture yield per unit area can be increased by increasing the breeding density.
However, when blindly increasing the breeding density leads to the aquaculture density exceeding the bearing capacity of the water body, the density is used as an environmental stress factor to have a negative impact on the growth and survival of the aquaculture object.
At this time, increasing the breeding density not only can not increase the yield and improve the efficiency of aquaculture, but may increase the failure rate of aquaculture.
It is generally believed that aquaculture individuals have different critical breeding densities due to species or at different stages of development, and under this density, the growth and survival of aquaculture individuals are positively correlated with the breeding density, and above this critical value, the growth and survival of aquaculture individuals are negatively correlated with the breeding density.
This is mainly due to the increase in breeding density, which leads to competition between farmed individuals in food and living space, and cultivated individuals, resulting in a decrease in growth rate, bait utilization and final yield.
The study found that the weight gain rate and survival rate of Roche marsh shrimp at lower culture densities were higher than those in the high-density culture group. The final quality of the juvenile crayfish decreased with the increase of culture density.
Under the condition of 60 days of freshwater culture, the survival rate of Penaeus vannabin (150/m3) exceeded that of the high-density group (850/m3) by 65%, and the body length and weight of shrimp cultured in the high-density group were only 75.1% and 45.9% of the low-density group, respectively.
The impact on farmed organisms is a long-term process, and farming density is only one aspect of evaluating the impact of farmed organisms, as it relates to the physiological condition and stress resistance of farmed organisms, which not only affect the subsequent transport and survival time of farmed organisms, but also have a significant impact on their marketing.
When selecting shrimp or fish, customers usually prefer individuals who are viable, smooth and non-damaged, and with the rise of intensive and high-density aquaculture, the influence of culture density is becoming more and more common, so considering the culture density on the physiological condition and stress resistance of farmed organisms is also an important factor.
At present, the research on the physiological state and stress resistance of aquaculture organisms mainly focuses on the protein level, mainly investigating the enzymatic activity of relevant enzymes in the blood of cultured organisms.
Some studies have found that the activity of stress-related enzymes, including alkaline phosphatase (ALP) and superoxide dismutase (SOD), is significantly reduced in some fish under high-density culture, while the activity of acid phosphatase (ACP) and lysozyme is not significantly different from that of individuals in the low-density group.
In addition, the activity of immune stress-related enzymes phenoloid oxidase (PO), ALP and antibacterial (UA) in the muscles was also reduced during high-density culture of shrimp, while the activity of SOD showed higher activity in the high-density group.
In particular, crustaceans have a relatively imperfect endocrine regulation mechanism, and the internal regulation mechanism under high-density breeding is not clear.
At the molecular level, the effect of culture density on the stress of P. chinensis was studied, with special attention to the expression of stress-related genes, which provided supplementary materials for the study of the stress mechanism of crustacean organisms.
P. sacs is an important species in the mainland aquaculture industry, and its live sales and high value have attracted much attention, and the culture technology of P. sacchar is relatively immature, and the yield is much lower than that of other shrimp species.
Therefore, culture density becomes a key factor affecting the production of Japanese p. sac, suitable culture density can increase production, but too high or too low density will increase risk and reduce profits.
The experimental results showed that under suitable water quality conditions, P. japonica could maintain a suitable growth environment at different densities, and the increase of culture density led to a decrease in growth traits, a decrease in survival rate and a significant change in stress-related gene expression.
Therefore, it is necessary to make full use of the water body to ensure high production and aquaculture profits, which is conducive to the sustainable development of the shrimp industry.