| At the temperature of 24±2℃, the mean total length of the newly hatched larvae of Mandarin fish was 3.73±0.10 mm (n=30) and the oval yolk sac was 1.316±0.153 mm3 (n=30) in volume, 0.43±0.04 mm (n=30) in diameter. After hatched 12h, the ventral fin of larvae was augmented and larvae could swim perpendicularly by tail swinging. The mean total length of 1 day after hatched (DAH) larvae (after hatched 24-26h) was 4.38±0.14 mm. 29 Sarcomere separated and nearly 60% the oval yolk sac disappeared, the diameter of the oil globule decreased a little to 0.40±0.02 mm. The mean total length of 2 DAH larvae was 4.47±0.17 mm. Mouth was obviously to be seen and could open weakly. The larvae could swim ahead kvelly, but slowly and weakly. At this period eyeball developed complete. The mean total length 3 DAH larvae was 4.94±0.19mm. The oral-pharynx cavity developed obviously and mouth gap was increased into 0.37±0.02 mm, with open and close strongly. At this period, the oval yolk sac volume was 0.210±0.011 mm3, 1/7 of the beginning volume. The mean total length 3 DAH larvae was 5.36±0.38mm. The mouth velum of larvae disappeared and there is the first appearance of the mandible and maxilla. The digestive tract came into be two bends and the intestines put through. The ability of the level swim of the larvae enhanced and the larvae began to prey initiatively. It is determined that the larvae started the primarily. At the 6 DAH, the oval yolk sac and oil globule disappeared completely that the larvae quite get into exogenous feeding. The mean total length became 16.50±0.74 mm when 15 DAH. The mean increase rate of the larvae total length was 0.85mm/d in these 15 day period. The fin-rays of the larvae of 15 DAH has almost developed completely. At that time the surface form of the larvae was similar to the juvenile except the larvae without scale. In course of larvae developing, it divided into three growth periods that the first is the endogenous feeding period with fast growth, the second is mixed feeding period with slow growth and the third is exogenous feeding period with fast growth. According to equation TL = aD3 + bD2 + cD + d, making a correlation analysis between the total length and the DAHs of larvae, we found that the growth model of the Mandarin fish larvae was TL = 0.0023 D3 + 0.0046 D 2 + 0.3041 D + 3.8909 (R2 = 0.9893, n = 238). After preying normally in 4 DAH, the correlation equation between mouth width(MW) and total length was(TL) was MW = 0.0607TL + 0.1743 (R2 = 0.9215, n = 162); the correlation equation between mouth hiatus(MH) and total length was MH = 0.2067TL -0.0423 (R2 = 0.9177, n = 147) . Both the mouth width and mouth hiatus were in direct proportion to the total length of the larvae. The Mandarin fish larvae usually prey in the dawn and dusk when 06:00 and 18:00 in the week light. It is 4 days that Mandarin fish larvae had the prey ability from newly hatching to the point of no return (PNR) which determined that the larvae depend the exogenous feeding in a early time and starved endurance of the larvae was in a comparative low level.In the condition of temperature25±1℃and pH: 6.73±0.21, observing two different size larvae (each of the total length were 11.98±0.74mm and 15.83±0.91cm) continuously for 24h, we found that the curve of two size larvae are similar in the change from day to night. The oxygen consumption in the afternoon was obvious lower than in the night, and both time appeared several similar maximal and minimum oxygen consumption. But the oxygen consumption of the different size larvae had obvious difference. Bigger and heavier larvae consumed more oxygen. And the asphyxia point of Mandarin fish larvae was far lower the same size larvae of the fish such catfish and so on.In the conditions of the temperature 23±2.2℃, pH: 7.01±0.25, according to the hydrobiology toxicity test, we made the acute toxicity test of Cupric sulfate(CuSO4), Chlorine Dioxide, Bromochlorodimethylhydantoin, Fenvalerate to the mandarin fish larvae. The result was that CuSO424h LD50 4.39 mg·L-1,48h LD50 3.33 mg·L-1,72h LD50 1.96mg·L-1,96h LD5 1.96 mg·L-1, the safe concentration 0.20 mg·L-1; Chlorine Dioxide 24hLD50 8.75 mg·L-1,48h LD50 7.87 mg·L-1,72h LD50 6.14 mg·L-1 96h LD50 3.66 mg·L-1,0.37 mg·L-1; Bromochlorodimethylhydantoin 24h LD50 6.49 mg·L-1,48h LD50 6.31mg·L-1,72h LD50 5.25mg·L-1,96h LD50 4.80mg·L-1,the safe concentration 0.48 mg·L-1; Fenvalerate 24h LD50 0.110 mg·L-1, 48h LD50为mm, 72h LD50 0.024 mg·L-1, 96h LD50 0.020 mg·L-1, safe Concentration was 0.002 mg·L-1. It indicated that the mandarin fish was more susceptive than the other fish. And Fenvalerate can not be used to prevent and cure the mandarin fish.
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