The techniques of artificial breeding and fry rearing of Murray cod (Macculochella peelii) in China

Abstract

as a new breed of freshwater culture in China, Murray cod (Macculochella peelii) has attracted much attention. In order to improve the culture benefit, This Article is concentrated on the artificial breeding and fry rearing techniques of Murray cod, including the selection and culture of parent fish, artificial inducing, insemination, hatching, the feeding start time for the fry, food switching, domestication and fish seed culture. This is a reference for the majority of breeding workers. Murray cod is endemic to the Murray-Darling River System, and it tops the four economic fishes in Australia and it is one of the largest freshwater fish in the world. The meat of Macculochella peelii is tender, delicious and thick, and there are few fish bones between muscles. It also contains 4 kinds of amino acids, EPA, DHA and other nutrients. It is high in protein and low in fat, so it is popular among the people. However, due to overfishing, environmental pollution and destruction of spawning grounds, its resource is decreasing day by day. Australia calls it the national treasure fish. Macculochella peelii has the characteristics of fast growth, strong adaptability to environment, high fecundity and survival rate, great disease-resistant ability, easy domestication and high conversion rate of artificial compound feed, so it is suitable for intensive culture in different culture areas [1]. In 1999, it was first introduced to Taiwan from Australia, and in 2001, it was introduced to the mainland of China [2]. At present, as a new breed of freshwater culture in China, the fish has attracted much attention and has great prospects for development. There are many related researches on Macculochella peelii[3-9]. This paper mainly introduces the industrialized artificial breeding technology of Macculochella peelii in China. 1. Artificial breeding 1.1 Selection and culture of parent fish The sexual maturity time of Macculochella peelii is 3-5 years old, and generally, more than 70% of the 4-year-old fishes are mature, the spawning is one batch a year, and the suitable water temperature is 16-20°C. Through the study, we found that under the same conditions, the breeding effect of the parent fish over the age of 6 was better than that of the parent fish at the younger age. We should choose the healthy fish without disease or injury and the body color should be normal. The weight of male is 4~10kg, the weight of female is 5~10 kg, and the ratio of male to female is 1~2:1. The selection of parent fish usually starts in autumn, and it needs about half a year of artificial intensive culture. We need to provide sufficient high protein feed, adjust the fat ratio, add vitamin C, vitamin E, n-3 HUFA and liver-protection products. The nutritional requirements of the parent fish vary with the water temperature. In autumn (September to November), when the water temperature is suitable, the protein required for nutrition is ≧45% and the fat required for nutrition is ≧15%; in winter (December to February), when the water temperature is lower than 13°C, the nutrition demand is high protein and low fat, and the proportion of fat is reduced. In spring (March to May), the water temperature is suitable, and the nutrition demand is maintained by low protein and low fat. There is a certain relationship between gonad development and water temperature (Fig. 1) [10]. 2020 2nd International Symposium on the Frontiers of Biotechnology and Bioengineering (FBB 2020) Published by CSP © 2020 the Authors 239 Fig. 1. The relationship between gonad development and water temperature In autumn (September to November), the water temperature is suitable, the gonad is in the II stage, and the gonad can develop to the III stage only after low temperature stimulation. Under 13~18 °C, it is in stage IV, and after the water temperature reaches 20°C for one week, it can be in the V stage. At this time, the abdomen of the parent fish expands, and the female’s genital pore is dark red or purple. We use a glass tube with a diameter of 4mm to export the egg for microscopical examination, and it can be found that the egg is an amber and translucent ball, with a diameter of about 3 mm. From the head to the tail, we push the abdomen of the male fish, and we can squeeze out the semen. After it is diluted by normal saline, we carry out microscopic examination to check the sperm density and viscosity, then we choose the male with good sperm quality as the parent sample. After stress operation such as fishing, the gonad development of the sexually mature parent fish will go through the process of degeneration and absorption, and the ovary contains yolk and primary oocyte, so it is not suitable to carry out fishing before artificial inducing [11]. 1.2 Artificial inducing In the process of artificial inducing, the most commonly used Pitocin is HCG or CPG, and the normal saline is prepared on site and then used on site. Use normal saline to dissolve the drug, and the dosage for each tail is not more than 5 ml, and then inject HCG 900-1000 IU per kg or HCG200 IU+CPG 5mg per kg into to female fish, while for male fish, the dosage is halved. Before catching the parent fish, we first use eugenol 10ml/m3 to anesthetize it, and then catch the fish, and then finish the injection within one hour. The injection position is the base of ventral fin or the base of pectoral fin. After injection, in order to prevent them from chasing and biting, we must put them in the birth pond alone. When the water temperature is 20~21°C[12], we inject HCG 1000 IU per kg. After 46~48 hours, they begin to ovulate. 2~3 hours after ovulation, we extrude the eggs and inseminate them, and the hatchability is 85.5%~90%; after 45~46 hours, we extrude the eggs and inseminate them, the hatchability is 70%~89%. The meiosis of different fish eggs is different. Within one hour after ovulation, the eggs may not reach the meiosis stage, and after three hours, the eggs may have passed the meiosis stage, which will greatly reduce the hatchability.