CẢI TIẾN VIỆC ĐỰC HÓA CÁ XIÊM (Betta splendens Regan, 1910) BẰNG CÁCH NGÂM TRONG 17α-METHYLTESTOSTERONE

Cá xiêm (Betta splendens) 1 ngày tuổi được đực hóa bằng cách ngâm trong túi polyethylene chứa 17α-methyltestosterone (17α-MT) ở các nồng độ 2,5; 5,0 và 7,5 mg/L có bơm oxy (thể tích oxy: thể tích nước bằng 2:1), mật độ 150 con/L trong 4 giờ. Kết quả cho thấy, tỷ lệ đực và đực hóa tăng khi tăng nồng độ hormone, với nồng độ 2,5 mg 17α-MT/L cá đạt tỷ lệ đực, tỷ lệ đực hóa là 88,89% và 78,26%. Nồng độ 5,0 mg 17α-MT/L và nồng độ 7,5 mg 17α-MT/L đạt tỷ lệ đực, tỷ lệ đực hóa là 100%. Khác biệt không có ý nghĩa (p>0,05) về tăng trưởng chiều dài và khối lượng của cá xiêm. Tỷ lệ sống 60 ngày sau khi nở là 54 - 89,89%, tỷ lệ sống giảm khi tăng nồng độ hormone 17α-MT trong nước ngâm. Kết quả cho thấy, nồng độ 2,5 mg 17α-MT/L là liều tối ưu để áp dụng chuyển đổi cá xiêm đực. Nồng độ 2,5 mg 17α-MT/L cá đạt tỷ lệ sống, hiệu suất đực hóa cao nhất là (86,22%, 76,81%). Với nhiều ưu điểm như đơn giản, chi phí thấp và có thể áp dụng ở mọi nơi nên có thể sản xuất cá xiêm đực bằng cách áp dụng phương pháp ngâm cá trong hormone 17α-MT với nồng độ 2,5 mg/L để đạt hiệu quả kinh tế tối ưu cho người nuôi. ABSTRACT The siamese fighting fish (Betta splendens) at one day old were masculinized by immersion in a polyethylene bag containing 17α-methyltestosterone (17α-MT) at concentrations of 2,5; 5,0 and 7,5 mg/L with oxygen pump (volume oxygen: water volume is equal to 2:1), density is 150 fish/L in 4 hours. The results showed that the male and masculinization ratios increased when the hormone concentration was increased, with a concentration of 2,5 mg 17α-MT/L, the male rate and masculinisation rate was 88,89%, and 78,26% respectively. Concentration of 5,0 mg 17α-M/L and concentration of 7,5 mg 17α-MT/L reached the male rate, the masculinization rate was 100%. The difference was not significant (p>0,05) in terms of length and weight growth of siamese fighting fish. The survival rate of 60 days after hatching was 54 - 89,89%, the survival rate decreases when the concentration of 17α-MT hormone in immersion water increases. The results showed that, concentration of 2,5 mg 17α-M/L was the optimal dose for converting male siamese fighting fish. Concentration of 2,5 mg 17α-MT/L, fish achieved the highest survival rate, masculinization efficiency respectively rate (86,22%, 76,81%). With many advantages such as simplicity, low cost and applicability everywhere, it is possible to produce male siamese fighting fish by applying the method of immersion fish in the hormone 17α-MT with a concentration of 2,5 mg/L to achieve efficiency economic efficiency optimal for farmers.

Modal characteristics and fluid–structure interaction vibration response of submerged impeller

Turbo pump is one of the elements with the most complex flow of liquid rocket engine, and as an important component of turbo pump, an impeller is the weak point affecting its reliability. In this study, a noncontact modal characteristic identification technique was proposed for the liquid oxygen pump impeller. Modal characteristics of the impeller under three different submerged media, air, pure water, and brine with same density as liquid oxygen, were tested based on the noncontact modal identification technology. Submersion state directly affects the modal frequencies and damping ratio. The transient vibration response characteristics of the impeller excited by the unsteady flow field was achieved combining with unsteady flow field analysis and transient dynamic analysis in the whole flow passage of the liquid oxygen pump. Vibration responses at different positions of the impeller show 10X and 20X frequencies, and the amplitude at the root of short blade is significant, which needs to be paid more attention in structural design and fatigue evaluation.

Elevated micro-topography boosts growth rates in Salicornia procumbens by amplifying a tidally driven oxygen pump: implications for natural recruitment and restoration

Background and Aims The growth rate of pioneer species is known to be a critical component determining recruitment success of marsh seedlings on tidal flats. By accelerating growth, recruits can reach a larger size at an earlier date, which reduces the length of the disturbance-free window required for successful establishment. Therefore, the pursuit of natural mechanisms that accelerate growth rates at a local scale may lead to a better understanding of the circumstances under which new establishment occurs, and may suggest new insights with which to perform restoration. This study explores how and why changes in local sediment elevation modify the growth rate of recruiting salt marsh pioneers. Methods A mesocosm experiment was designed in which the annual salt marsh pioneer Salicornia procumbens was grown over a series of raised, flat and lowered sediment surfaces, under a variety of tidal inundation regimes and in vertically draining or un-draining sediment. Additional physical tests quantified the effects of these treatments on sediment water-logging and oxygen dynamics, including the use of a planar optode experiment. Key Results In this study, the elevation of sediment micro-topography by 2 cm was the overwhelming driver of plant growth rates. Seedlings grew on average 25 % faster on raised surfaces, which represented a significant increase when compared to other groups. Changes in growth aligned well with the amplifying effect of raised sediment beds on a tidally episodic oxygenation process wherein sediment pore spaces were refreshed by oxygen-rich water at the onset of high tide. Conclusions Overall, the present study suggests this tidally driven oxygen pump as an explanation for commonly observed natural patterns in salt marsh recruitment near drainage channels and atop raised sediment mounds and reveals a promising way forward to promote the establishment of pioneers in the field.