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    Induction of molting in hatchery-reared mud crab Scylla serrata juveniles
    De la Cruz, Joanna Joy Y. (University of the Philippines Visayas, 2014-03)
    The effects of lime, temperature and autotomy of chelipeds on growth, survival and molting of mud crab Scylla serrata juveniles were investigated under laboratory conditions. Hatchery produced S. serrata (45-day old) at the intermolt stage with internal carapace width of 2.0-2.3 cm and body weight of 1.7-2.2 g were exposed to lime concentrations of 0, 100, 200 ppm at daily and weekly application, temperature of ambient, 29, 32 and 35 °C and subjected to autotomy. The juveniles were allowed to molt twice prior to termination. The survival of juveniles declined with increasing levels of lime. Mean survival rate of juveniles without lime was 47% while 100 and 200 ppm lime ranged from 29 to 32%. No significant differences were found in the specific growth rate (% SGR) and molt interval (days) in all lime treatments after the first and second molts. All juveniles held in 35 °C had 100% mortality in the first molt due to incomplete molting therefore it was excluded from data analysis. SGR of crab juveniles in the ambient (2.75 ± 0.15%) and 29 °C (3.20 ± 0.18%) were comparable but significantly different (P<0.01) with those juveniles in 32 °C (4.12 ± 0.39%). The molt interval of the crab juveniles after second molt was significantly shorter with increasing temperature (29 °C: 32 ± 0.80 days, 32 °C: 28 ± 1.11 days) compared to ambient temperature (39 ± 0.93 days). The mean survival of juveniles in various temperature levels upon termination was 62, 85 and 65% for ambient temperature, 29 and 32 °C, respectively. Juveniles with intact chelipeds (5.80 ± 0.47%) and one cheliped autotomized (5.45 ± 0.30%) had a significantly higher SGR compared to juveniles with both chelipeds autotomized (4.20 ± 0.52%) in the first molt but no significant difference was observed in the second molt. This trend was observed because the autotomized chelipeds were not fully regenerated after the first molt. The molt interval was significantly shorter in the autotomized juveniles compared to juveniles with intact chelipeds. The interval was 36, 28 and 23 days for intact, one and two chelipeds autotomized, respectively. The survival of juveniles with intact chelipeds (60.61 ± 6.06%) was comparable with autotomized chelipeds (one cheliped: 59.60 ± 4.04%; two chelipeds: 47.22 ± 2.78%). Based on the results, the suggested optimum temperature level for rearing S. serrata juveniles was at 29 °C. Likewise, autotomy of one cheliped can promote molting without adversely affecting the growth and survival of the juveniles. On the other hand, the application of lime did not improve the molting of juveniles due to occurrence of high pH and alkalinity. This also resulted in the low survival and growth of Juveniles.
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    Chemical changes in a limed and flooded acid sulfate fishpond
    Baylon, Carlos C. (University of the Philippines at Los Baños, 1981-10)
    Field and laboratory studies were conducted on an acid sulfate soil in Carles, Iloilo with the following objectives: a) to characterize the soils in the pond bottom and along the dikes of an acid sulfate fishpond; b) to follow-up some chemical changes occurring in the flooded acid sulfate ponds, and c) to evaluate the effect of liming on these chemical changes. The pH (1 :1 soil-water) of the air-dried soil samples collected from the pond bottom and along the dikes of the nursery ponds ranged from 2.2 to 4.6. This was significantly correlated with the lime requirement, extractable Al, active Fe and Mn, acetate-soluble sulfate and total sulfur content of the soil. In the field experiment, before lime treatment, the waters of the nursery ponds exhibited decreasing pH with time as well as increasing concentrations of dissolved Al and Fe. The level of Mn in the water was low due to the small amount of active Mn present in the soil. Acidity in the pond waters after a heavy rain was mainly due to the leaching of sulfuric acid from the dikes. Three lime treatments were used in the study: I-lton/ha of lime applied along the dikes and 3 tons/ha on the pond bottom, II - 3 tons/ha of lime on dikes and 1 ton/ha on the pond bottom, III - 4 tons/ha of lime on dikes and no lime on the pond bottom. Treatment II could be considered the most effective way of applying lime since the ponds in this treatment exhibited the highest mean water pH compared to the ponds of the other treatments. Fish mortalities were observed in one of the ponds (NP10 in Treatment III) which may be traceable to the low pH and high Al concentration in the pond water. The applied lime on the dike was not able to control the acidity because it washed down by the rains and covered with eroded soil. The SMP buffer method of determining lime requirement overestimated the lime required to control the acidity of the water in acid sulfate ponds.