The fisherman's idea is simple, they want the fish to grow fast, but sometimes this is not something that can be solved by throwing more feed. If the growth characteristics of fish are not comprehensively considered, blindly increasing the amount of bait will only accelerate the destruction of water quality and even produce the opposite effect.
In fact, only at a specific growth stage, targeted increase in the amount of bait can achieve the ideal breeding effect, so it is necessary to understand the growth law of fish.
< h1 class= "pgc-h-arrow-right" > so what are the laws of fish growth? </h1>
In order to adapt to different environments, organisms exhibit different growth characteristics. Fish grow similarly to higher mammals, and there is also a period of fastest-growing "puberty" before sexual maturity, after which the growth rate of fish becomes very slow. Overall, the growth law of fish weight and body length shows an asymmetrical "S" shape (as shown in the figure below), and the juvenile stage, juvenile and juvenile stages before sexual maturity are the main growth periods, with the fastest absolute growth rate and the highest demand for nutrients.
As shown in the figure above, increasing the amount of bait and improving nutrition during the main growth period of fish can accelerate the growth of fish and increase aquaculture production in the shortest possible culture cycle. So, in addition to increasing feeding during the growing season, what other factors are related to the growth of fish?
To sum up, there are five main aspects.
<h1 class = "pgc-h-arrow-right" >1</h1>
As with almost all vertebrates, the size of individuals is largely determined by genetic factors, that is, the size of individual species, and their offspring are generally large, and fish are no exception.
The growth rate of fish is closely related to the size of individuals, and the growth rate of large species is much faster than that of smaller ones, which is also consistent with common sense. According to this standard, 76 major farmed fish in China can be divided into 4 types: small fish, medium-sized fish, large fish, and giant fish.
There are 8 species of small fish
Among the small fish, the more common ones are loach, spotted catfish, Chinese wutang fish, large silver fish, etc., in addition to zebra seahorses, male fish, mountain female trout and ayu with the title of "king of freshwater fish".
▲▲Small fish commonly found in aquaculture, except for loach, the rest of the economic value is very high
There are 33 species of medium-sized fish
Many of the medium-sized farmed fish are well-known aquatic products, common ones are yellow jaw fish, yellow eel, mandarin fish, California perch, crucian carp, silver crucian carp, tall white salmon, white spotted salmon, true seabream, black seabream, yellow croaker, semi-slippery tongue ray, red spotted grouper, Xu's flattened fish, dark eastern bream, blue gill sunfish and so on.
▲▲Medium-sized fish commonly found in aquaculture, the economic value is generally higher
In addition, less common species are yellow-capped flounder, flowertail pepper seabream, purple-red snapper and Otaki six-line fish (wild Otaki six-line fish can often be caught along the coast of Qingdao, but artificial culture is rare, and its seedlings are shown in the figure below).
▲▲ The seedlings of Otaki hexaline fish have a beautiful body color
There are 30 species of large fish
Many of China's bulk freshwater fish are large fish, and the four large fish of "grass carp" are among them. Common freshwater species include carp, catfish, catfish (catfish in the United States), long-snouted catfish, Su's round belly (also called freshwater shark), spoon-sturgeon (platypus), rainbow trout, salmon, short-lipped giant carp (also known as freshwater white pomfret) and so on.
Common marine species are eel, mullet, cobia, turbot, turbot, redfin oriental bass, American striped perch, flower perch, oval pomfret, Du's amberjack and so on.
There are 4 species of giant fish
The largest fish belong to the sturgeon family, such as the Chinese sturgeon, Siberian sturgeon, Shi's sturgeon, and Russian sturgeon. Since sturgeon generally need more than 10 years to be sexually mature, if it is not specialized in fry breeding, it only needs to be fed for about 1 and a half to 2 years to be marketed.
Siberian sturgeon
Note: The captive farming industry of sturgeon may be affected by this outbreak, and some media have said that the domestication and breeding of sturgeon is prohibited, but the specific substantive policies and documents need to be further waited and seen.
<h1 class = "pgc-h-arrow-right" >2. Sex of farmed fish</h1>
For most aquaculture fish, females grow faster than males, such as semi-slippery tongue mackerel, mullet, star flounder, etc., and some species have little difference in growth rate between male and female individuals, the most typical example is the giant yellow croaker. For a few species such as tilapia, individuals in males grow faster than females.
There is also an interesting phenomenon that the growth rate of a very small number of female and male individuals in fish varies with weight. Mandarin fish is such a fish, when the weight is less than 170g, the growth rate of male and female mandarin fish is not significantly different; at weight 170-800g, the female grows significantly faster than the male; when the weight is greater than 800g, the reversal occurs, and the growth rate of the male begins to catch up with the female. But in general, within 2 pounds, the average growth rate of females is greater than that of males, and more than 2 pounds is that males are greater than females.
From the growth characteristics of mandarin fish, we can get such an inspiration - if the production goal is to develop large mandarin fish, then choose as many male fry as possible, and vice versa, select as many female fry as possible. If this arrangement is made when the seedlings are released, then in the predetermined time, higher yields can be obtained and the economic benefits will be higher. The problem is that therefore, the sex control technology of mandarin fish may have greater potential for development in the future.
<h1 class= "pgc-h-arrow-right" >3. Growing water temperature of farmed fish</h1>
First of all, for broad-temperature fish, their growth rate accelerates with the increase of temperature. For example, the flower perch farmed in Guangdong is faster than in the Yellow and Bohai Sea regions, the Russian sturgeon farmed in Henan is faster than in Beijing, and the Shi's sturgeon stocked in the Wuhan Reservoir is faster than in Russia.
Secondly, for narrow warm fish, that is, cold water fish, sub-cold water fish, warm water fish and warm water fish, the same is in line with this law. For example, the well-known cold-water fish, rainbow trout, grows significantly faster at 14 °C than at 9 °C; warm-water giant yellow croaker grows faster at 25-35 °C than at 17-22 °C. The precise control of water temperature, the current factory breeding model is completely achievable.
<h1 class="pgc-h-arrow-right" >4. Hybrid new varieties grow faster than ordinary varieties</h1>
Hybrid offspring have the trait advantages of both parents, and have greatly improved in terms of growth rate, stress resistance, fertility, yield and quality. For example, the growth rate of lotus carp obtained by hybridization of lotus red carp (female) and Yuanjiang carp (male) is 21.2%-23.2% faster than that of the parent and 30.05%-38.57% faster than that of the mother; the growth rate of the hibiscus carp obtained by the hybridization of the scattered mirror carp (female) and the Xingguo red carp (male) is 40% faster than that of the mother and about 60% faster than the father.
Loose-scaled mirror carp
<h1 class= "pgc-h-arrow-right" >5. Water quality: pH, water fertility, dissolved oxygen</h1>
Other environmental factors, such as pH, water fertility, dissolved oxygen, etc., will affect the growth of fish, and their mechanism of action is different.
pH
pH is a comprehensive indicator in the aquaculture water body, the dynamic change of the pH of the aquaculture water body is a normal phenomenon, but when the change range is too high, it is prone to problems. In traditional pond culture, the phytoplankton in the water during the day in the summer will photosynthesis, absorb carbon dioxide and produce a large amount of oxygen, which will lead to an increase in the pH of the water body - the pH in the morning is 6.5-7.0, and the noon will rise to 9.5-10.0, when the change range exceeds 3 units, the water quality should be adjusted in time.
Fertility of water quality
Different fish prefer different water quality, and in general, silver carp, bighead carp, duckbill and other plankton-feeding fish prefer fertile water quality. Some hypoxic-tolerant warm water fish also prefer to inhabit fertile water, such as carp, crucian carp, eel and so on. Cold-water fish such as rainbow trout and Atlantic salmon and carnivorous fish such as mandarin fish and real snapper prefer fresh and lean water quality.
Typical cold-water fish, the Atlantic salmon
dissolved oxygen
Under artificial culture conditions, cold-water fish have high requirements for dissolved oxygen, requiring 2/3 of the time in 24h of the day to be more than 6mg/L, and the rest of the time can not be less than 5mg/L. For example, salmon trout, its suitable dissolved oxygen content is 6-7mg/L, but when the dissolved oxygen is reduced to 3.0mg/L, it will begin to suffocate and die.
Another example is ayu, during the breeding period, the dissolved oxygen content can not be less than 5.0mg/L, otherwise the growth will be inhibited, when the dissolved oxygen content in the water body is reduced to 2mg/L, it will suffocate to death.
In contrast, warm water, warm water fish have less requirements for dissolved oxygen. Our most common carp can still survive normally when the dissolved oxygen is reduced to 1mg/L, and the floating head phenomenon occurs only when the dissolved oxygen is further reduced to 0.2-0.79mg/L.
carp
<h1 class= "pgc-h-arrow-right" >6</h1>
In the natural state, the growth of fish needs to occupy a certain amount of space and resources, when the space becomes smaller or the resources decline, the growth of fish will be stressed. In the same way, when too many fry are stocked in the pond, the space and resources allocated evenly by each fish will be greatly reduced, and the coercive effect will seriously limit the growth of fish. Ponds with excessive breeding density will even have the phenomenon of "eating only food without growing meat".
The researchers had studied the optimal growth density of Nile tilapia, and the experiment set up six parallel controls with culture densities of 45/m³, 54/m³, 63/m³, 72/m³, 81/m³ and 90/m³. The results showed that the growth rate was fastest when the density of Nile tilapia reached 54 fish/m³, and when this density was exceeded, the growth and immune function of Nile tilapia were suppressed.
Nile tilapia
In addition, controlling a reasonable breeding density can also effectively reduce the probability of disease occurrence and increase the success rate of aquaculture. Especially in recent years, the promotion of the concept of ecological breeding, multi-variety, low-density polyculture mode is becoming more and more common, which can produce higher quality, better meat quality of aquatic products, naturally more popular with consumers.
<h1 class="pgc-h-arrow-right" > summary</h1>
The growth of fish is directly affected by external ecological conditions, which are more pronounced than in mammals. In addition to the direct correlation with cultured species and their sex, nutritional conditions, water temperature, water quality (pH, dissolved oxygen, salinity, fertility), etc., artificial management of culture patterns, culture density and other humane management will also affect the growth of fish. Grasping these elements and applying them to production practices makes it easier to obtain higher economic benefits.
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