Fish farming

Mullet is a wide salt species and widely distributed in tropical and subtropical coastal waters around the world, it is known as a mass fish because of the quality of meat and the right price. compared to other expensive fish such as grouper, barramundi.

Mullet is also considered as an object of economic value in the countries of the Mediterranean, Isael, Tuynisia, Hong Kong, Taiwan . due to growing fast and easy to breed with other species. In addition, fish eggs are also a favorite food of Chinese people, so please

(Photo: shop.uwphoto)

It has been seen as a research object in many fields from the 1960s onwards. However, in Vietnam this object is very little attention to as a breeding object, they are mainly exploited naturally in the sea and brackish water so there is very little research on this object.

1. Summary of biological characteristics of mullet.

The mullet family is a very large family in which about 13 species are considered to be subject to aquaculture, but most notably Mugil cephalus species because they have a very wide distribution, fast growing and large size. when reaching adulthood.

Our country has 13 species of fish, of which at least 5 species in the South: M. cephalus, M dussumieri (new name Liza subviridsis), Liza macrolepis, Liza vaigiensis and Valamugil cunnesius. According to the report of the Ministry of Fisheries (1996), in the estuarine area, we often see 5-7 valuable species.

Mullet is a large salt species, they can live and grow well in brackish, saline and saltwater environments. In subtropical regions, in one study (Cardona, 2000), small juveniles (<200mm) and fingerlings (201-300mm in length) are concentrated all year round in fresh or brackish water. For adult fish, their habitat varies depending on the season and it is related to the process of reproduction, when they begin to breed, there is a tendency to avoid freshwater flows. However, this study also showed a difference for the fish populations in the tropics, especially in the Indo-Pacific region. Poor fish growth in freshwater and low salinity while growing well in brackish, saline and saltwater areas (up to 70ppt) and they suffer from the lowest salinity shock, especially in temperature conditions. low. Hotos and et al (1998) in an experiment shocking salinity for juvenile fish (2.6cm body length) from initial salt concentration of 20ppt to salinity 35-80ppt (5ppt for each distance) showed that fish caught The head died at a salt concentration above 45ppt and died 100% at 70ppt.

Mullet can withstand temperatures below 10 ^o C, there are very few documents mentioning the effect of temperature on the growth and reproduction of mullet. Most studies on mullet are arranged at a temperature of 20-30 ^o C.

Mullet in larval stage to juveniles are zooplankton species, when they mature they transfer the food spectrum to planktonic plants, suspended organic mulch and bottom vegetation (lab-lab: plus born between bottom algae and microorganisms). In addition to fertilizing conditions, fertilizing stimulates the development of algae as natural food for mullet, they can also be supplemented with rice bran, peanut oil cake, soybeans or peanut flour.

M dussumieri in the brackish water area of ​​the Red River system reaches the size of 135-195 cm (equivalent to 113-167g), Liza soiny's opposite fish reaches 280-370cm, the counterpart reaches 295-360 cm (Vu Trung Tang, 1994). The area of ​​Tam Giang lagoon (Hue) is about 501 cm (1.120 g). Mature mullet are 2 years old, and fish in the brackish lagoons have gonads to stage IV, spawning in the lagoon. Absolute fertility reaches 7500-27,000 eggs. Particularly, mating fish only have fish with low gonads (below stage III) (Vo Van Phu, 1995). Mullet, Mugil cephalus grow faster than other mullet in the mullet family. Females usually grow faster than males and also achieve larger sizes. In farming conditions, after one year they can reach 300g, 1.2kg after two years and over 2kg if reared after 3 years.

Mullet has the habit of living in the population, and this behavior is strongest in the breeding season, the fish often concentrate into large groups migrating to deep waters in the sea to breed. Mullet is a species that breeds seasonally and breeding season of fish lasts from October to April next year, however in the subtropical water bodies the breeding season may be shorter (until January-February next year). Mullet reach sexual maturity at 3 years of age with an average body length of about 33 cm in males and 35 cm in females. The reproductive power of common fish is proportional to the weight and length of the fish body, the bigger the fish is, the higher the reproductive power. Children weighing about 1.5 kg have a reproductive capacity of 1-1.5 million eggs (Pillay, 1990). Caviar has a diameter of 0.9-1mm. The fertilized eggs hatch into larvae for about 16-30 hours at a temperature of 20-24 ^o C. The mullet larvae are very small (2.5-3.5mm) and tend to avoid strong light. Newly hatched eggs and larvae drift off the coast at some time during the year (breeding season) and seasonal fish fry in estuarine areas are considered as breeding grounds for breeding fish.

2. Breeding fish

(Photo: ag.auburn)

Usually in practice, there is no farming of mullet, but they are cultured with other subjects such as bamboo shoots, barramundi and productivity can reach an average of 400 kg / ha in India. In Hong Kong, Taiwan and Isael, mullet are farmed with Chinese carp and fish is the main target. Stocking density is up to 10,000-15,000 / ha (7.5cm in size) with 1000-2000 Chinese carp. When was big. more (12cm), the remaining trimmed mullet were about 3500con / ha. Pharmaceutical feed provided includes: rice bran (first 2 months) and then peanut oil cake, rice bran. In addition, the pond is also fertilized with organic fertilizer to enhance the natural food source. The yield is from 2500-3500kg / ha.

In Taiwan, mullet is farmed with bamboo shoots (2000con / ha), Chinese carp (3250 / ha) and carp (500 individuals / ha) at a density of 3000con / ha. Fish reach 300g after 1 year and 1.2 after 2 years. In addition, mullet is also cultured with tilapia, carp and carp with a total density of about 12,300 individuals / ha. After 4 months, raising mullet reached 100g. In breeding females, mullet are usually faster than males and their eggs are used in the processing of specialty foods, so steroids (17a-Methyltestosterone and Ethynyloestradiol) have also been used through food to control the chemical sex of mullet.