| The salinity tolerance of Pseudosciaena crocea during early development(newly-hatched larvae, mouth-opened larvae, yolk-sac disappeared larvae, oil globulesdisappeared larvae, fry and30-day-old juvenile) was examined at salinites of5,10,25,40and45. The mortality, mean death time (MDT), median death time (DT50), andmedian lethal salinity-72h (MLS-72) were employed as indicators of salinity tolerance.The results showed that suitable salinity for30-day-old juvenile, yolk-sac disappearedlarvae, mouth-opened larvae, fry, and newly-hatched larvae was range from5.5to41.0,6.8to23.3,8.2to39.4,9.3to26.7,18.9to33.1, respectively. Therefore, the salinitytolerance of30-day-old juvenile of P.crocea is rather strong, especially it can tolerantlow-salinity of5.5. The results lay a theoretical foundation for desalting culture and thefresh water treatment for white spot disease of P.crocea. In normal seawater, the mediandeath time (the point-of-no-return. PNR) at different developmental stages withoutfeeding was determined as follows: newly-hatched larvae (8.6d)> mouth-opened larvae(6.5d)>30-day-old juvenile (5.5d)> yolk-sac disappeared larvae (4.6d)> fry (4.0d)>oil globules disappeared larvae (1.8d). These indicate that the feeding of exogenousnutrients should be enhanced before the oil globules disappeared, which will help toimprove low-salinity tolerance and survival of P.crocea’s larvae.Due to the limit of the producing areas of P.crocea, transport is needed before lowsanility culture, so make an efficient transportation plan is very important. Make threekinds of plans for transport:(1) directly transport in normal seawater;(2) directlytransport in low-salt water;(3) domesticate in low-salt water before transporting inlow-salt water. Considering the mortality rates of larvae during transportation and lowsanility culture, the process of domesticate in low-salt water was no use. The mortalityrates of plan2was slightly higher than directly transport in normal seawater, but it wasno significant; During the stage of low sanility culture without food, the mortality ratesof plan2has no significant difference with the other two plans, but there are significantdifference between plan1and plan3. And during the stage of feeding with food inlow-salt water after transport, there is almost no death after8-day breeding and the larvae becoming steady, that means larvae of P.crocea could adapt to the environment oflow salinity (salinity10‰). At the same time, cortisol of larvae were measured. Aftertransport, the stress level change of plan2was not significant. the change of the othertwo plans was wavy, showed the stree level change was obvious. It is concluded that:the best way to2months’ larvae of P.crocea breeded in low-salt water is the plan2, thatis “directly transport in low-salt water”.Experiments were conducted to determine the feeding, growth and survival rate ofeight-months juvenile of P.crocea during low salinity domestication in an indoorcirculating culture system. The juveniles were domesticated at salinity10pptenvironment for30-days and transported to the aquarium facilities at Shanghai OceanUniversity. After8hours transportation, the juveniles were cultured in indoorhalf-closed circulating system at the salinity of10. After5days environmentaladaptation and80days of feeding period, the length of P.crocea increased from5.31cmto8.36cm, the rate of growth was0.04cm per day. The weight increased from2.59g to8.50g, adding0.07g per day. The survival rates was70.5%. Perhaps the commercialfeed and the low grazing rate more or less lead to low growth rate of juveniles.Therefore, the result is expected to lay the foundation for the indoor desalination cultureof P.crocea in the coastal reclamation and estuary district with low salinity waters. |
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