Supuestos generales

The main source for juvenile fish in the study area is a hatchery in Son La town, which was established by the government in the 1960s and became privatized in 2004. A total of ten hatcheries exist in this province, but only four hatcheries (Son La, Song Ma, Thuan Chau and Phu Yen) are able to conduct artificial reproduction. The remaining hatcheries (or nurseries, respectively), such as the hatchery/nursery of Yen Chau, Mai Son and Moc Chau, partly purchase fry from bigger hatcheries and raise them up to a certain size before selling them to farmers. According to the operators of the Son La hatchery, they produced 15 million fish in 2005, 2-3 million of which were sold to Yen Chau.

In the Yen Chau hatchery/nursery, which was privatized in 1993, only common carp are produced, while all other fish are purchased as fry from the hatchery in Son La. The manager of the Yen Chau hatchery reported a fry survival rate of 30-40% and a total sold volume of 1.5 million fry in 2005. Both Son La and Yen Chau hatcheries grow some fish up to marketable size in order to gain additional income by selling the fish directly to consumers.

The most important fish species produced by local hatcheries include grass carp, mud carp, Indian carp such as mrigal and rohu, common carp, silver carp, bighead carp, silver barb and (monosex) tilapia. Most of the fish produced in these hatcheries are grass carp (≥ 50%) followed by mud carp and mrigal. Table 9 shows the names of the fish in Latin and Vietnamese. The Vietnamese word “Cá Mè” stands for both silver carp and bighead carp, and the word “Cá Trôi” refers to mud carp, mrigal and rohu. This can regularly lead to confusion, since farmers as well as consumers often consider the different fish species to be the same, in both terminology and species. During the interviews, it was often the case that the exact fish species could not be clarified. Therefore, the following text frequently refers to the fish groups (mud carp/mrigal/rohu and bighead/silver carp) instead of the individual species.

In 1967, the Son La hatchery started collecting broodstock fish (except tilapia) originating from the province Son La. The broodstock is kept year round in net cages in ponds. However, over the years, larger fish were collected from farmers and added to the stock. In the hatchery, fish reproduction usually takes place in the first half of the year. It is

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typically the case that broodstock males and females are randomly collected and crossed through the application of hormonal injections.

The typical feeds applied to small grass carp in the hatchery are shown in Figure 15. Once grass carp are hatched and start feeding on exogenous food, they are supplied the ground yolk from duck eggs. After two days of feeding, fry are transferred to a fishpond and supplemented with grass and leaves, germinated rice and soybean meal.

Table 9: Typical fish species produced in the hatcheries in Son La and Yen Chau in English, Latin and Vietnamese languages

Common name in English Latin name Vietnamese name Grass carp Ctenopharyngodon idella Cá Trắm cỏ Mud carp Cirrhinus molitorella Cá Trôi Việt Nam

Mrigal Cirrhinus cirrhosus Cá Trôi Mrigal

Rohu Labeo rohita Cá Trôi Rôhu

Common carp Cyprinus carpio Cá Chép

Silver carp Hypophthalmichthys molitrix Cá Mè trắng Bighead carp Artistichthys nobilis Cá Mè hoa Nile tilapia Oreochromis niloticus Cá Rô phi Common silver barb Barbodes gonionotus Cá Mè vinh

Individual farmers seeking new fish for stocking either contact a farmers’ union or buy them directly. They purchase the fish either from hatcheries in Son La or Yen Chau town, from fish traders of other provinces or from other farmers who grow fish to a certain size. Farmers’ unions (e.g. of a village or commune), on the other hand, organize fish purchases from distant locations or make appointments with the fish traders. Often, farmers buy fish from different sources and practice multiple stocking.

Figure 15 shows the route of grass carp from siring to the farmer’s grow-out pond as well as the stage when they are purchased by farmers. When farmers were asked about the stocking size of fish, they regularly talked about “chopstick” or “toothpick” size; therefore, the “farmers’ language” had to be “translated” into the “language of the interviewer”, which regularly required some time for clarification.

Very seldom do farmers purchase fish as fingerlings, since they usually prefer advanced fry with a body length of 2-3 cm. This is because the transport of these fish requires less effort and the price of small fish is lower. According to the Son La and Yen Chau hatcheries, 50-70% of fish are sold when they are at this size. However, in 32% of the ponds belonging to those farmers who were interviewed with the questionnaire, grass carp were purchased from local nursery ponds and then stocked with bigger sizes (≥ 300 g fish-1_{) for}

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further grow-out. An argument for this technique is that there is a quicker growth potential for larger fish compared to small fish. Additionally, there is a lower risk for the presence of fish seed, which is infected with disease from the hatcheries.

Figure 15: The route of grass carp movement from siring to the grow-out pond, the stage when they are sold to farmers and the feed they receive in hatcheries

Typical prices for juvenile grass carp in the region are shown in Table 10. Prices usually depend on fish size and are the same for most of the produced fish species. However, several species are more expensive including common carp and monosex tilapia, which are sex-reversed by means of synthetic testosterone. Only rarely do farmers buy common carp and tilapia from local hatcheries, which can be explained by the fact that these fish species reproduce naturally in farmers’ ponds. However, a continuous supply of fish is often not guaranteed, thus farmers’ stocking often depends on fish availability rather than on long-term planning.

The hatchery staff members usually transport fish by jeep or motorbike with an oxygen supply. They report that fish quality decreases during long transports to remote areas.

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If the purchased quantity of fish is large, they are often delivered by the hatchery; otherwise, farmers purchase fish directly and transport them in plastic bags placed in a basket on a motorbike or carried while walking. Also in these cases, fish can be negatively affected during the course of long transports. It was also observed that farmers frequently release fish into their ponds without preconditioning them to the new environment, which often leads to high fish mortality in the following days.

Table 10: Typical prices for juvenile grass carp in Son La province (state: April 2005) Size of grass carp Local prices

Fry 2-4 VND fry-1

Advanced fry (length 2-3 cm) 40 – 100 VND fry-1

Fingerlings ~ 1 000 VND fingerling-1

Young fish (e.g. ~ 500 g) 20 000 - 25 000 VND kg-1

VND = Vietnamese Dong

The typical stocking period takes place from March to June for fish purchased from the hatcheries. During their last major stocking procedure, farmers stocked an average of 1.6 fish m-2 in grow-out ponds and 7.1 fish m-2 in nursery ponds, where grass carp were usually the most prevalent fish species in terms of numbers as well as biomass (survey 2). The number of fish stocked as well as the combination of species generally depends on both fish availability and farmers’ liquidity. Also, personal preferences and experiences (“silver carp do never grow in my pond…”) influenced farmers’ decisions regarding the species combination in the ponds. The farmers interviewed often experienced difficulties remembering the exact amounts of stocked fish, especially when the stocking activity had taken place a long time ago. Additionally, multiple stocking and frequent removal and transfer of fish makes it difficult to estimate the real numbers of fish stocked. Since common carp and tilapia reproduce in farmers’ ponds, farmers usually have no indication of the present amount of those species.

During their last production period, several of the interviewed farmers (4%, survey 2) also reported culturing less typical fish species such as pirapitinga (Colossoma/Piaractus

brachypomus) and catfish (Clarias sp.). The farmers apparently did so based on the advice of

local radio and television broadcasts or fish traders. Additionally, 7 out of 85 farmers (survey 2) reported that they stocked snails in their pond.

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