A Comprehensive Analysis of Grouper Aquaculture Techniques and Management Methods
Grouper belongs to the order Perciformes, with an elongated oval body that is slightly laterally compressed, a large mouth, an auxiliary maxillary bone, and fine pointed teeth, some of which are enlarged into canine teeth. The body is covered with small ctenoid scales, sometimes often embedded beneath the skin. The dorsal and anal fin spines are well developed. The caudal fin is rounded or concave. Body color varies greatly, often brown or red, with stripes and spots. It is a warm-water large and medium-sized marine fish. Grouper is rich in nutrients, with delicate white flesh similar to chicken, and has long been known as "sea chicken." Grouper is also a premium food fish that is low in fat and high in protein. It has been promoted by Hong Kong, China and Macao, China as one of the four famous fish of our country and is an essential delicacy at high-end banquets.
Seedling Selection
When selecting, attention must be paid to the quality of the fish. Fish that are robust, lively, disease-free, free of scale damage, and with good skin luster should be selected for farming.
The main methods for farming adult grouper are cage culture and pond culture, with cage culture being more common. Cage culture of grouper is an intensive farming method with high stocking density, easy management, and relatively high production efficiency, so it has developed rapidly. In introducing adult fish farming techniques, cage culture is the main focus, while pond culture and indoor cement tank culture can refer to cage culture.
Farming Conditions
The environment of the farming sea area should have the following conditions: good shelter from wind, small waves, and no typhoon strikes; sandy bottom, gravel bottom, or rocky bottom is preferable, with water depth above 4 m at low tide; smooth tidal currents with moderate flow velocity, with the velocity inside the cage preferably maintained at 0.20 m/s to 0.75 m/s; the lowest water temperature in winter not below 15°C, with no fewer than 200 days at water temperatures of 22°C to 28°C; clear water quality. Grouper has a wide adaptability range to salinity, able to survive between 11‰ and 41‰, with the optimal salinity at 25 to 32‰, pH = 7 to 9, and dissolved oxygen above 5 mg/L; free from pollution by industrial and agricultural wastewater and urban sewage, with no large influx of freshwater during heavy rain seasons, salinity not below 16, and transparency above 1.5 m; good transportation conditions, convenient for live fish transport and feed supply.
At present, grouper seedling breeding has not yet reached production-level requirements, so the fish used for farming are still mainly juveniles captured from natural sea areas and raised as seedlings. For farmed grouper juveniles, those caught by handline are preferable. When selecting, attention must be paid to the quality of the fish. Fish that are robust, lively, disease-free, free of scale damage, and with good skin luster should be selected for farming.
Stocking Size and Density
Stocking density is greatly related to the flow velocity of the farming sea area. Sea areas with smooth flow can have higher density, while those without should have lower density. Generally, for a 3×3×3 (m) cage, when the fingerling size is below 50 g per fish, about 2,500 fish can be stocked per cage, and when the size is below 150 g per fish, about 1,000 fish per cage.
That is to say, a production yield of about 200 kg per 3×3×3 (m) cage is relatively suitable. For seawater cage culture of grouper, under the condition of a water temperature of 25°C, a stocking density of 60 fish/cubic meter to 70 fish/cubic meter is preferable. In production practice, about 500 adult fish are raised in a 3 m×3 m×3 m cage. The results show that when the stocking density is 15 fish/cubic meter and 30 fish/cubic meter, grouper grows relatively fast. When the stocking density is increased to 60 fish/cubic meter, the growth rate is similar to the former, with no obvious difference. However, when the stocking density is increased to 120 fish/cubic meter, the weight gain per fish decreases, the feed conversion ratio increases greatly, and the survival rate decreases significantly. This proves that an adult fish stocking density of 60 fish/cubic meter is relatively suitable. For cage culture of red-spotted grouper in the Xiangshan Port sea area of Zhejiang, when the individual weight is 100 g to 150 g, a stocking density of 90 fish/sq m to 70 fish/sq m is appropriate.
Feed and Feeding Techniques
Grouper is a carnivorous fish, and the main feed used for feeding is small miscellaneous fish with high freshness. Generally, according to the size of the grouper, a fish cutting machine is used to cut the small miscellaneous fish into suitable sizes before feeding. Due to differences in the species of feed fish, the feeding coefficient fluctuates between 5 and 12. When blue round scad is used as feed, the feeding coefficient is relatively low, while when bigeye fish is used, the feeding coefficient is relatively high. With the rapid development of the grouper cage culture industry, the supply of feed fish has become increasingly tight, and promoting artificial compound feed for grouper is imperative.
Practice shows that grouper has relatively high requirements for feed palatability, including hardness, color, and taste. It prefers soft pellets and light-colored, bright feed. If the pellets are too hard, there will be spitting behavior. Its adaptability to soft pellet feed is clearly superior to hard pellet feed. There is a relatively long adaptation process from feeding small miscellaneous fish to changing to artificial compound feed, and feeding training must be carried out before feeding compound feed. In artificial compound feed for red-spotted grouper, the suitable crude protein content is 40% to 50%; in compound feed for green grouper, the suitable protein content is 51% to 55%, and the suitable fat content is about 9.87%. If the fat content in the feed is appropriately increased, more protein can be used for fish body growth rather than being consumed as an energy substance, which can save protein and improve the utilization rate of feed protein.
Wet dough feed prepared with fishmeal as the main protein source was used to feed young salmon grouper and fry, and growth was best when the protein content was 40% to 50% and 54%, respectively. Dry compound feed prepared with fishmeal and casein as protein sources was used to feed salmon grouper, and the optimal protein content was 50%. There is little interspecific variation in the muscle amino acid composition of grouper. The composition pattern of 10 essential amino acids is lysine:leucine:arginine:valine:threonine:isoleucine:phenylalanine:methionine:histidine:tryptophan = 9.8:9.1:7.7:5.2:5.0:4.9:4.8:3.1:2.6:1.0. This amino acid composition pattern can provide a reference for formulating grouper compound feed. The electrophysiological thresholds of red-spotted grouper and green grouper in response to alanine stimulation are 10 mol/L to 9.9 mol/L and 10 mol/L to 9.6 mol/L, respectively, significantly lower than those of other fish.
This may be related to their living among bottom reefs, with degraded visual function and relatively developed olfactory function. This provides good prospects for research on olfactory attractants for grouper. Grouper has special requirements for feed pellet size. When feeding adult fish, the particle size of the pellet feed should not be less than 6 mm. If the pellets are too small, appetite is not high.
Feeding techniques have a relatively large impact on the effectiveness of grouper farming. Under the environmental condition of a water temperature of 25°C, the digestion speed of grouper is about 20 hours to 24 hours. Therefore, in the sea area of the South China Sea from May to October, grouper is fed once a day, generally between 9 a.m. and 11 a.m. From November to December and from March to April, it is fed once every two days. In winter, when the seawater temperature drops below 20°C, it is fed once every 3 days to 4 days. Each feeding amount accounts for about 3% to 5% of body weight. When the water temperature is suitable, the feeding amount is larger, and when the water temperature is lower or too high, the feeding amount is reduced.
In production, the feeding amount is generally determined by observing the feeding state of the grouper, stopping when appetite weakens. The general principle of feeding is: during neap tides with slow currents and clear water, and when the water temperature is suitable, feed more; otherwise, feed less. The daily feeding amount is generally controlled at about 8% of the fish body weight. At each feeding, a small amount should first be scattered little by little and slowly across the area. After the previous batch of feed is consumed, scatter the next batch, until the fish are full and no longer compete for food. Never pour the feed into the cage all at once, to avoid feed waste and environmental pollution. Grouper will never eat food that sinks to the bottom. Because grouper eats by swallowing, the size of the feed must be smaller than the fish's mouth diameter. Feeding should also follow the principles of fixed quality, fixed quantity, and fixed time. In pond culture, attention should also be paid to setting up feed platforms and feeding at fixed points, so as to improve feed utilization and facilitate the removal of leftover feed and maintain good water quality.
Graded Rearing
When stocking fingerlings, they should be reared in grades according to fish size. Theoretically, the smaller the individual differences, the better, but in actual operation this is difficult to achieve. Because when the size differences among fish are small, feeding is uniform, which is beneficial to growth.
Daily Management
Choose reasonable cage and raft densities to prevent oxygen deficiency accidents. During the farming process, in addition to feeding, frequently observe and inspect the fish's growth, feeding, activity, and body color, and also frequently check whether the cages are damaged and how much fouling organisms are attached. Regularly remove fouling organisms attached to the cages to keep water flow inside and outside the cages smooth. Methods such as fouling organism preventive agents, mechanical cleaning and chemical treatment, and co-culture of natural enemies of fouling organisms can be used to remove them. Regularly grade and sort to maintain consistency in grouper body size within the same cage. Because fish have the effect of large fish suppressing the growth of small fish and cannibalism when hungry, regular grading should be carried out to make the size of grouper in the cage uniform.
Polyculture with a small number of sea bream species and omnivorous fish, so that:
① It can remove leftover feed at the bottom and fouling organisms on the cages.
② Because sea bream species have strong food competition, it can stimulate the appetite of grouper.
③ It can make full use of water space and feed resources and improve farming efficiency.
Reinforce iron anchors and cables, and regularly check the cages for damage to ensure safe production. Especially before typhoons arrive, defenses should be strengthened, wind and wave resistance measures should be enhanced, safety work should be done well, and production safety should be ensured. Regularly monitor water quality and protect the farming environment. Monitor farming water according to the Class I seawater quality standard issued by the state, which is conducive to the normal growth of grouper and delicious flesh, and prevents accidents caused by water quality deterioration.