Tran Ngoc Hai

Current status of freshwater prawn culture in Vietnam and the development and transfer of seed production technology

In Vietnam, the giant freshwater prawn Macrobrachium rosenbergii is becoming an increasingly important targeted species, as its culture, especially in rice fields, is considered to have the potential to raise income among improverished farmers. The production of M. rosenbergii based on aquaculture reached over 10 000 tons per year in 2002, having increased from about 2500 tons since the 1990s. Until recently, lack of a stable supply of seed had been an important obstacle to the further expansion and development of M. rosenbergii culture, but cumulative research on larval rearing, especially in the 1990s, has led to the development of new seed production technology based on the ‘modified stagnant green water system’. Following its disse mination by the efforts of provincial authorities, hatchery operators, and farmers, the freshwater prawn seed production industry developed rapidly in the Mekong Delta with over 90 hatcheries producing 76.5 million postlarvae in 2003. This is considered to have affected the expansion of rice-prawn farming in the Mekong Delta, leading to increased aquacultural production in the region. This paper reviews the current status of freshwater prawn culture in Vietnam and background history, and presents a socioeconomic evaluation of seed production technology implementation.

The effects of dietary lipid sources and lecithin on the production of giant freshwater prawn Macrobrachium rosenbergii larvae in the Mekong Delta region of Vietnam

The giant freshwater prawn, Macrobrachium rosenbergii, is cultured widely in the Mekong Delta region of Vietnam but it is often difficult or expensive for hatchery operators to purchase commercial diets used as a feeding supplement to Artemia nauplii. Therefore, in the present study, the effects of lipid sources and lecithin on the growth and survival rate of M. rosenbergii larvae were examined in order to develop suitable hand-prepared larval diets for seed production of M. rosenbergii in this area. Six egg custard diets consisting of various ratios of lipid (originating from soybean oil and squid oil) and lecithin were used for rearing Macrobrachium rosenbergii larvae. Treatments in which larvae were fed diets containing squid oil exhibited the highest body length and survival rates (7.14–7.43 mm and 51.1–68.1%, respectively), and differed significantly from other treatments (P<0.05). Use of dietary soybean oil yielded the lowest body length and survival rates (6.29–6.75 mm and 22.0–48.7%), respectively). The supplementation of dietary lecithin did not increase final body weight but did improve larval survival rates. The n-3 HUFA content of prawns fed dietary squid oil was higher than those of animals provided with other diets. These results indicated that the most appropriate diet for rearing M. rosenbergii larvae is the diet containing 3% squid oil and 1.5% lecithin.

Erratum to: Sodium fluoride influences calcium metabolism resulting from the suppression of osteoclasts in the scales of nibbler fish Girella punctata

The influence of sodium fluoride (NaF) on calcium metabolism was examined in nibbler fish (marine teleosts). Two days after the administration of NaF (5 μg/g of body weight) (around 10−4 M in fish), we showed that plasma calcium levels significantly decreased in NaF-treated nibbler fish. In addition, we detected fluoride in the treated scales by use of a scanning electron microscope with an energy-dispersive X-ray microanalysis, indicating that NaF directly affects their scales. Therefore, the influence of NaF on osteoblasts and osteoclasts in the scales was examined. In the scales of NaF-injected nibbler fish, tartrate-resistant acid phosphatase (TRAP) (osteoclastic marker enzyme) decreased, although alkaline phosphatase (osteoblastic marker enzyme) was activated. To confirm the effect of NaF on osteoclasts, furthermore, the mRNA expressions of osteoclastic markers (matrix metalloproteinase-9 and TRAP) were decreased significantly 2 days after incubation. In barred knifejaws, plasma calcium levels decreased as they did in nibbler fish. Therefore, NaF functions in both osteoblasts and osteoclasts and then influences calcium metabolism in marine fish. In the marine environment, high levels of fluoride (1.2–1.5 mg F−/l) (around 10−5–10−4 M) are present in seawater. It is probable that teleosts living in seawater efficiently use fluoride to regulate their blood calcium levels.

Sodium fluoride induces hypercalcemia resulting from the upregulation of both osteoblastic and osteoclastic activities in goldfish, Carassius auratus.

The influence of sodium fluoride (NaF) on calcium metabolism was examined in goldfish (fresh water teleost). At 2days after administration of NaF (500ng/g body weight; 5μg/g body weight) (around 10(-5) to 10(-4)M in goldfish), we indicated that plasma calcium levels upregulated in both doses of NaF-treated goldfish. To examine the mechanism of hypercalcemia by NaF treatments, therefore, direct effects of NaF on osteoblasts and osteoclasts in goldfish were investigated by an original assay system using teleost scale which has osteoblasts, osteoclasts and bone matrix. Alkaline phosphatase activity in the scales increased with the treatment of NaF (10(-6) and 10(-5)M) during 6h of incubation. Also, tartrate-resistant acid phosphatase activity increased after exposure to NaF (10(-5)M) at the 6h of incubation. To investigate the osteoclastic activation, the mRNA expression of osteoclastogenesis related factors were examined. The receptor activator of the nuclear factor-κB ligand (RANKL) which is known as a factor for osteoclastogenesis, increased in the NaF-treated scales after 6h of incubation. The ratio of RANKL/osteoprotegerin (osteoclastogenesis inhibitory factor) significantly increased after 6h of incubation. Resulting from the increase of RANKL mRNA level, the expression of transcription-regulating factors was significantly increased. Furthermore, the expression of functional genes, cathepsin K and matrix metalloproteinase-9 mRNA, was significantly increased. In our knowledge, this is the first report concerning the effects of NaF on osteoblasts and osteoclasts in teleosts. We concluded that NaF influences calcium metabolism via osteoclastic activation in goldfish.

Clown knifefish ( Chitala ornata ) oxygen uptake and its partitioning in present and future temperature environments

It has been argued that tropical ectotherms are more vulnerable to the projected temperature increases than their temperate relatives, because they already live closer to their upper temperature limit. Here we examine the effects of a temperature increase in environmental temperature to 6°C above the present day median temperature (27°C) in the freshwater air-breathing fish Chitala ornata, on aspects of its respiratory physiology in both normoxia and in hypoxia. We found no evidence of respiratory impairment with elevated temperature. The standard metabolic rate (SMR) and routine metabolic rate (RMR) in the two temperatures in normoxia and hypoxia increased with Q10 values between 2.3 and 2.9, while the specific dynamic action (SDA) and its coefficient increased from 7.8 to 14.7% in 27°C and 33°C, respectively. In addition, Chitala ornata exhibited significantly improved growth at the elevated temperature in both hypoxic and normoxic water. While projected temperature increases may negatively impact other essential aspects in this animals environment, we see no evidence of a negative impact on this species itself.

SURVEY ON FISH DISEASES ON COBIA AND GROUPER OF MARINE FISH CAGE CULTURE IN NAM DU ISLANDS, KIEN HAI DISTRICT, KIEN GIANG PROVINCE

The study was conducted to investigate the current status of marine fish diseases in cobia and grouper cage culture in Nam Du islands, Kien Hai district, Kien Giang province. Cobia cage culture (n = 25) and grouper cage culture farmers (n = 25) were directly interviewed from October to December 2013. The results showed that the diseases on cobia and grouper yearly occurred but mainly in two periods of April - May and July to September. The main diseases were reported during cobia culture including ulceration (72%), hemorrhage (64%) and exophthalmia (100%). Parasitic infection was also reported. Chemical was not commonly used during culture period, but antibiotics were used to treat the bacterial diseases. The most common antibiotics were tetracycline, streptomycin, rifamycin and oxytetracycline. Farmers reported grouper diseases comprising ulceration (50%), hemorrhage (38.4%), exophthalmia (11.5%) and parasite infections (23.1%). During husbandry practices, some chemicals (Potassium permanganate, Iodine, Copper sulfate) and antibiotics (rifamycin, oxytetracycline, tetracycline, ampicillin, nutroplex) were limitedly used.

TECHNICAL ASPECTS AND COSTS BENEFITS OF THE MODEL MANGROVES - SHRIMP IN NAM CAN DISTRICT, CA MAU PROVINCE

The study was conducted from August to December 2014. Thirty seven mangroves-shrimp farmers in Nam Can district, Ca Mau were randomly selected for the interview. The aim of this study was to assess the costs and benefits and to identify the factors affecting the model. The results showed that the average of farm area was 2.1 ha, with forest cover of 35.9%, and water depth in ditch of 1.3 m, and in marsh land of 0.5 m. The age of tree was 2 to 17 years (6.7 years in average). The stocking time for shrimp and crab was 4.7 and 5.2 times/year respectively; and stocking density was 16.8 shrimp/m 2 and 0.6 crabs/m 2 . The shrimp and crab survival rate was 1.3% and 3.8%, respectively. The average yields of black tiger shrimp, crab, natural shrimp and fish were 196 kg/ha/year, 61 kg/ha/year, 89 kg/ha/year and 71 kg/ha/year, respectively. Total cost was 23.9 million VND/ha/year; average income was 86.3 million VND/ha/year; net income was 62.3 million VND/ha/year; profit margin was 2.9. Factors affecting the productivity were survival rate, stocking frequency, tree age and water depth. Profit and profit margin of this model were lower in farms with tree age of 9 years compared to those of younger tree ages. Additionally, profit was affected by productivity of black tiger shrimp, crab, and fish; and stocking density of shrimps and crabs.

TECHNICAL ASPECTS AND ECONOMIC BENEFITS OF THE JUVENILE CRAB NURSERY IN LINING TANK IN NAM CAN DISTRICT, CA MAU PROVINCE

Study on technical aspects and economic benefits of the juvenile crab nursery in lining ponds/tanks in Nam Can district, Ca Mau province was conducted from August to December 2014. Thirty five farmers were interviewed in Ham Rong commune, Nam Can district, Ca Mau province. The results showed that the average area of the lining tanks was 9.6 m 2 ; with 0.3 m in depth and 100% net substrates. Stocking density was 256.7 inds/m 2 . 40% of farmers used fresh krill (sergestidae) as feed and 60% of farmers combined fresh krill (sergestidae) and pellet feed. Survival rate reached 84.9% and the average productivity was up to 237.4 inds/m 2 . The total production was 986,000 inds/year/farmer. The total production cost was 18.8 million VND/production run; the income was 5.1 million VND/run (121 million VND/year/farmer) and 94% of farmers made profit. The study also determined factors affecting the efficiency of the rearing model including (i) nursery area; (i) megalops price; (iii) stocking density; (iv) survival rate and (v) selling price.