Largemouth Bass Pond Culture in China: A Review

Largemouth bass micropterus salmoides natives to freshwater area of North America, which is a kind of famous global economic fi sh, and belongs to Centrarchidae, Perciformes in taxonomy. The fi sh has been extensively cultured all over the world, due to it some advantageous traits such as delicious meat, strong disease resistance and fast growth speed. This review will summarize the studies aimed at the pond culture technology of largemouth bass in China from artifi cial breeding, offspring culture, fi ngerling and commercial fi sh culture, to diseases prevention. Which should be useful for further studies and the aquaculture industry. Review Article Largemouth Bass Pond Culture in China: A Review Rui Li, Zheng-Yong Wen*, Yuan-Chao Zou, Chuan-Jie Qin and Deng-Yue Yuan College of Life Sciences, Conservation and Utilization of Fishes resources in the Upper Reaches of the Yangtze River Key Laboratory of Sichuan Province Neijiang Normal University, Neijiang, Sichuan 641100, China Dates: Received: 25 January, 2017; Accepted: 13 February, 2017; Published: 14 February, 2017 *Corresponding author: Zheng-Yong Wen, College of Life Sciences, Neijiang Normal University, Neijiang, Sichuan 641100, China, Tel: + 86 18582681220; Fax: + 86 18582681220; E-mail: https://www.peertechz.com


Introduction
Largemouth bass was fi rst introduced into China in Guangdong province in the early 1980s of last century.
Since then, this kind fi sh was quickly spread to culture in other provinces, following with a rapid improvement of the production. As a result, the largemouth bass culture industry has become an important composition of Chinese fi shery. To date, the fi sh was mainly cultured in pond, especially largely culture in the province of Guangdong, Sichuan and Zhejiang, and it has become the major freshwater aquaculture species in China. The average yield of this fi sh can reach about 37500 kg/ ha in Guangdong province , so the pond culture technology is worthy to spread.
According to the market demand, the largemouth bass pond culture technology is divided into four stages, including the artifi cial breeding, fry rearing, fi ngerling rearing and marketable fi sh culture. The average level of pond culture technology is relatively high, but the development of aquaculture technology in different regions is not balanced.
Based on the four culture stages mentioned above, this paper summarize the technology of pond culture by combining the literatures of recent years with the practical experience of the aquaculture work, which should be useful for the largemouth bass industry development.

Artifi cial Breeding
Broodstock cultivation: The artifi cial breeding of largemouth bass is mainly performed in southern China region.
Usually, healthy fi shes (1-1.5 kg, 2-3 years old) are selected to be as the candidate broodstock, and then put them into ponds with the male and female ratio 1:1 or 3:2. The breeding ponds are primary earthen ponds outside. Each pond area is required about 0.2 hectare with the water depth of 1.5-2 m, the slow fl owing water is also needed. As a fi ltering fi sh, some silver carps can be cultured in the pond to regulate the water quality and improve the pond usage rate [1].
The stocking density of broodstock should be 0.2-0.5 kg/ m 2 , which also could appropriately adjust according to the water quality and the pond condition. During the breeding season, high quality food must be provided to ensure the gonad development, such as fresh fi sh and compound feed are required, which need to be feed 1-2 times a day, and a 3-5% daily feeding amount of the total weight is necessary. Reducing the amount of food suitably one month before spawning, and pouring fresh water into the pond for 1-2 hours every 2-3 days to promote gonad maturation. The pond aerator should be turned on when it is necessary [1]. The earthen ponds area is required about 500-1500 m 2 with the water depth of 0.4-1 m. use the same method to set the artifi cial nests in the earthen pond [2,3]. Finally put 20-30 pairs of broodstocks in the earthen pond every 667 m 2 .
The injection of oxytocin: The reproduction of appropriate water temperature was 18-26, with 2 0-24 is better. In the process of production, oxytocin is injected into the fi sh body when the water temperature reaches the condition, and the main oxytocin used for injection including LRH-A 2 and HCG.
According to the specifi c circumstances, the numbers of injection time need 1 or 2 times by intraperitoneal injection (IP injection). For one-time injection, the LRH-A 2 d o se of injection need 5 g/kg of female fi sh bodyweight, while the HCG need a dose of injection at 800-1000 IU, meanwhile, the dose should be half for male fi sh [4]. For two-times injection, the 30% of total dose should be used in the fi rst injection, and the rest for the second injection. The interval time between the two injection actions need 9-12 hours.
The spawning and hatching: The effect time of oxytocic hormone is about 1-2 days, and classically the fertilized egg will be found adhere to the fi sh nest mesh, then move the fertilized egg to hatching pools together with the fi sh nest mesh. The hatching time of fertilized eggs is related to the water temperature, and the time is 45 hours when the water temperature is 18-21, but only 32 hours when the temperature is 22-23. It is best to maintain the micro fl owing water during the whole incubation process to ensure high dissolved oxygen in the water. The newly hatched larvae is only 0.7 cm in length and can swim in the cluster. The fry should be remain in the original pool at this time, and the fry begin to feed when the yolk is absorbed completely in three days after hatching [2].
Removing the fi sh nest and transferring the fry in the fryrearing pond when all the fry could swim freely, then the stage of fry culture is starting.
It should be noted that the largemouth bass is one kind of multiple spawning fi sh, so the brood stocks can spawn again if breeding condition is exist [5,6].

Fry Culture
The overview of fry culture: The fry culture means that feeding the larva fi sh from which is just begin to eat food to the fi ngerling stage that the body l ength is about 3 cm, and this fi ngerling is also called summer fi ngerling because of it is cultured usually in the summer in China. At this cultivation stage, the fry of largemouth bass is small and poor adaptability.
T h e model of fry culture including ement pond culture and earth pond culture, and the whole stage will last about 30 days depend on the water temperature.
Cement pond culture: The cement pool area is required for 30-50 m 2 with the water depth of 1 m, and equipped with separate inlet, drainage and aeration equipment. Thoroughly clean and disinfect the pool before the larva fi sh entering the pool, then move the larva fi sh to the pond and the density is required for 2000 tails/m 2 [7].
The small zoop lankton should be fed at the beginning of the breeding season, such as rotifers or artemia larvae, and the frequency should be 2-3 times every day. The food should be at 5-7 % bodyweight and properly adjust according to the feeding condition. We had better to transfer the fry in the earth pond when the fi sh grow to 1.5-2 cm long, and reduce the cultivation density properly. At this time, the fry should be fed with macrozooplankton zooplankton, such as the cladocerans, copepods and tubifi cidae. The food intake of fry increased gradually when the body length is above 2cm, so we start to feed fi sh pulp, then feed the small pieces of fi sh gradually.
Earth pond culture: The earth Pond area is required for 667-2000 m 2 with water depth of 1-1.5 m, and also need to equip with separate inlet, drainage and aeration equipment the same with cement pool. Using the medicine such as quicklime and tea seed meal to clean and disinfect the pond thoroughly before the lar v a fi sh entering the pool, then add nutrients into the pond to raise the reproduction level of the rotifer, cladocera and copepod, which is the food of the larva fi sh, so their biomass will peak in turn. The feeding density of larva fi sh is 50000 tails per 667 m 2 .
Starting to feed tubifi cidae and fi sh pulp when the fi sh grows to 2 cm long. The daily feeding amount accounts for 5%-10% of the fi sh weight, and make the appropriate adjustment according to the weather and feeding condition of fi sh. The fry grow to 3 cm long need about 30 days, then transfer the fry to different ponds according to the different length of body, meanwhile the stage of fi ngerling culture is starting [8].
Management key points: Adding fresh water into the pond regularly to improve the growth rate and survival rate of fry. The frequency at one time per 5-7 days is better, while exchange part of the original water in the pond. Using the net to fi lter out the rough fi sh and injurious insect, and to avoid the water fl owing into the bottom of the pool directly to make the water muddy.
Largemouth bass is one kind of carnivorous and fi erce fi sh, and the differentiation of individual size occur easily in the process of culture, then the fi sh will kill each other especially when the food supply is insuffi cient. So the adequate food should be provided fi rst, and make sure that the fry in the one pond is the same batch and the body length is tidy.
In the culture process, we should screen out the fi sh of different sizes to do the graded feeding, in order to ensure the size of fries are similar in the same pond, especially when the water temperature maintains at 20-24 to keep the rapid growth rate of fry.

Fingerling Culture
The overview of fi ngerling rearing: The fi n g e rling culture means that feeding the fi ngerling fi sh from 3 cm to about 5-6 cm long, or even longer. After 4-5 months of careful feeding, generally speaking, the summer fi ngerling will grow to 13-20 cm in length and 40-200 g in weight, which is called large size fi ngerling. The specifi c stocking density is determined according to water quality conditions and breeding needs. If the water quality is good, fi sh stocking density could be more higher, otherwise should be lower. If we want to cut down the breeding time, it is appropriate to reduce the stocking density.
In this breeding process, the fi ng e rling should be screened in time, and fed in different ponds according to the body size, meanwhile the culture density should be reduced with the gradual growth of fi ngerling. The stocking density for 5 cm long fi ngerling is 10000 tails per 667 m 2 , while for 10 cm long fi ngerling is 5000-6000 tails. The practice has proved that the cultivation method mentioned above that screening in time and graded feeding is the important to improve the survival rate of fi ngerlings [9][10][11].
The main food for fi ngerling is the fi sh surimi and pieces, also including some artifi cial compound feed. The feeding frequency are 2-3 times per day, and the feeding amount is 5-10% of the bodyweight. If the water temperature is appropriate and the management is correct, the fi ngerling size will reach to 10 cm or longer for 2 months, then we should transfer the fi ngerling to the pond for marketable fi sh culture.
Management key points: After summer fi ngerlings entering the pond, the enough food should be supported in time to make sure that the growth rate of most fi ngerlings is same, then the internecine condition of the fi ngerling will decrease and Survival rate will increase [12].
In addition, the scientifi c way of feeding is also important.
First of all, the pond should set a feeding area, and make all the fi ngerlings feed in this area to Increase the feeding effi ciency.
Secondly, we should extend the feeding time as far as possible, so that every fi sh can eat the food and get full. Otherwise, the food which not be eat by fi sh in time will sink to the bottom, not only to waste food, but also cause deterioration of water quality [13].

Commercial Fish Culture
Pond conditions: The pond area is required for 0.3-0.5 ha with water depth of 1.5-2 m, and the other equipment is the same with the fi ngerling pond. In addition, the pond needs to be equipped with the aerator and standby generator enough because of the high breeding density. Transferring the fi ngerling in the pond in one week before cleaning and disinfecting the pond completely [14].
Breeding methods: Transferring the fi ng e rling of 10 cm long to the pond. The fi ngerling should be healthy with tidy size to avoid or reduce the phenomenon of cannibalism. The stocking density of the fi ngerling is about 3 tails per m 2 , and the density can be raised if the feeding condition is good. The fi ngerling need to be disinfected by 3-5 % salt water before entering the pond to kill parasites and pathogenic bacteria.
Because of the fi ngerling is enough to get hurt and high oxygen demand, so we must move it into the pond in the sunny morning, and not to do it in the gale or stormy weather [15].
Some small amount of silver carp, bighead carp and grass carp can be cultured mix with the largemouth bass in the pond to regulate water quality by purging feed residue and controlling the growth of plankton, but the body size should more longer than 10 cm.
Management key points: The correct feeding way: In the fi rst few days after entering the pond, the fi ngerling need to adapt to the environment and do not to eat food right now, so we should properly feed in the following 2-3 days. The good fi sh feed including ice f r esh fi sh and artifi cial compound feed. The ice fresh fi sh should not be spoiled, and cut it to the appropriate size. The protein content of artifi cial compound feed should be 40-45 %. The feeding is required for at least two times per day, and the feeding amount is 5-10 % about the fi sh body weight for feed with the ice fresh fi sh, but 3-8% for feed with the artifi cial compound feed. In addition, the feed i ng amount should be adjusted properly according to the weather, water tem p erature and feeding situation. For example, the f e eding amount should be raised from July to September, because both the water temperature and growth speed of fi sh are at high levels, but the amount should be reduced in December due to the low water temperature. Meanwhile, the feed type cannot be too simple, and sometimes we must add vitamins and minerals in the food, in order to maintain the normal nutritional requirements of largemouth bass [16][17][18].

The Prevention and Treatment of Fish Diseases
In fact, fi sh diseases are frequent occurrence because of the farmers constantly improve the pond culture density for the higher yield and benefi t. Some diseases will bring huge economic losses to farmers if it happens, so the prevention of diseases is very important. In order to prevent diseases and improve the water quality, the farmer must sprinkle lime In addition, farmers should regularly check that whether the disease is happened, and treat actions must be taken as soon as possible. Some common diseases, symptoms and the primary prevention methods are listed below.
The sodden branchial dise a se: The fi sh gills show a white color and some part of them are rotten when the disease happened. In addition, the sick fi sh usually swim alone and eat few food. The treatment way is to use the 3% salt solution soak sick fi sh for 10-15 minutes, meanwhile feed the oral antibiotic drugs or sulfa-drugs [22].

The enteritis disease:
The sick fi sh usually shows a swollen abdomen and anus, and the yellow blood outfl ow from the anus if we press the abdomen lightly. The treatment way is to use the chlorine dioxide disi n fect the culture water, meanwhile add the oxytetracycline in the fi sh food to feed.
The nocardiosis disease: The appetite of sick fi sh is getting worse, and the body color changes to black. The kidney and muscle appear the white bulging pustule. The treatment way is to kill all the pathogenic bacteria by using the disinfectants before the fi sh entering the pond, and using the glutaraldehyde disinfect the culture water at the epidemic season of disease [23].