Survival and development experiment

Survival and development experiments
In all three trials, larval survival and development
showed a consistent relationship with rotifer density
(Table 1). In Trial 1, Z1 survival increased from 0%
to 68.3% as rotifer density increased from 2 to 40/mL,
the trend remained the same for Z2 and cumulative
survival to Z3 was highest at 40/mL, the highest
density set for the trial. Analysis showed that differences
between treatments were significant (P

Kết quả (Việt) 1:

Survival and development experimentsIn all three trials, larval survival and developmentshowed a consistent relationship with rotifer density(Table 1). In Trial 1, Z1 survival increased from 0%to 68.3% as rotifer density increased from 2 to 40/mL,the trend remained the same for Z2 and cumulativesurvival to Z3 was highest at 40/mL, the highestdensity set for the trial. Analysis showed that differencesbetween treatments were significant (P<0.05or P<0.01).In Trial 2, although larval survival was generallyhigh, as density increased from 20 to 60/mL, cumulativesurvival to Z3 increased from 74.4% to 94.7%;these differences were significant (40 vs. 20, 30/mL,P<0.05; 60 vs. 40, 30, 20/mL, P<0.01). As densityfurther increased to 80/mL, survival rate droppedslightly, possibly due to water quality deteriorationcaused by excess rotifers.Trial 3 had the poorest survival, nevertheless,larval survival increased with density again, and Z1161survival jumped from 24.0% to 73.3% as densityincreased from 40 to 60/mL (Table 1); the resultsindicated that rotifer density was particularly criticalfor larvae of poor hatch quality.Apart from survival, development of early larvaewas also generally enhanced by an increase in rotiferdensity (Table 2). For Trial 2, at densities ≥60/mL,mean Z1 duration was about 0.5 day shorter than forthose reared at densities ≤30/mL while cumulativedevelopment to Z3 was about 1 day shorter (P<0.01).The difference was also significant in Trial 3; at adensity of 60/mL, Z1 mean duration was 1 dayshorter than those at densities of ≤40/mL (P<0.01).Thus, rotifer density not only significantly affectssurvival, but also the development of early larvae ofthe mud crab.Fed with rotifers alone, a few larvae could metamorphoseto the megalopa stage, but mass mortalityoccurred at late zoeal stages (Table 1). Even whenrotifer density was increased up to 200/mL, larvalsurvival was not significantly enhanced (Trial 3,Table 1); thus, nutritional deficiency may be thereason for the mass mortality of late larvae.Since rotifers were not a good diet for late larvae,in Trial 2 a treatment of replacing rotifers (40/mL)with Artemia at Z4 was established. Compared totreatments in which rotifers continued to be thelarval diet, the mortality of late larvae was significantlyreduced and overall zoeal survival ratesreached 58.7% (Table 3), showing that Artemia wasa suitable diet for late larvae. However, this raisedthe question as to when a diet change should takeplace. To answer this question, Trial 3, comprising14 treatments, was designed and included replacementof rotifers by Artemia at each zoeal stage. Theresult of the trial showed that among all diet treatments,rotifer replacement by Artemia at Z2 or Z3, ormixed rotifer and Artemia from Z3 had the bestoverall zoeal survival (Table 3). Statistical analysisshowed that survival using these three feeding
regimens was significantly higher than others
(P<0.01) while differences between them were not
significant. At the same time, larval development
using these three diet combination treatments was
also significantly enhanced with the average zoeal
development generally several days (3–7) shorter
than other treatments (Table 4).
It was noted that in Trials 1 and 3, if rotifers were
fed at late larval stages, a proportion of Z5 larvae
moulted to Z6, an extra larval stage, before metamorphosis
to megalopa. However, this did not occur
in treatments in which Artemia was added at earlier
larval stages and also in Trial 2 (Tables 1 and 3).
This phenomenon does not appear to have been
reported previously for Scylla sp.
Although megalopae from all treatments were fed
with Artemia and maintained in identical conditions,
megalopae from treatments to which Artemia was
added no later than Z4 generally had higher survival
rates (>80%) than those in which rotifers were still fed
after Z4 (<50%) (Table 5). The results suggested that
poor nutritional conditions during the zoeal stages
might have delayed effects on megalopa survival.