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    Salinity tolerance of the angelwing clam, Pholas orientalis larvae
    Aguaras, Lovie Grace P. (Division of Biological Sciences, College of Arts and Sciences, University of the Philippines Visayas, 2011-03)
    Pholas orientalis, locally known as “diwal” is one of the commercially important bivalves in the Philippines due to its delicate and sweet taste. An experiment was conducted to determine the salinity tolerance of the 24-hour-old larvae of this clam when reared in different salinity levels of 25, 30, 35, and 40 ppt. The experiment lasted for 15 days at a rearing temperature of 25° C - 27° C. Determination of survival rates and water change were done twice every week. The data gathered were then analyzed using one-way ANOVA. Results showed that survival rates were significantly high at salinities of 30-35 ppt and were significantly low at salinity levels of 25 and 40 ppt. It was also observed that there was an increasing trend of mortality with prolonged exposure to different salinity levels. This could be attributed to the limited osmoregulatory capabilities of the larvae. When reared at low salinity levels, larvae were faced with the danger of too much water entry which eventually led to death. Meanwhile, when reared at high salinity levels, the larvae died due to outward movement of water which resulted to dehydration. Information on the salinity levels that could be tolerated by diwal larvae will be an important factor in the development of larval rearing techniques for successful hatchery operations. The juveniles or seeds produced in the hatchery could be used to restock the depleted resources in the wild.
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    The effect of common table salt added in different levels of water salinity as culture medium on growth and survival of prawn larvae Peneus monodon Fabricius
    Abeto, Mario N. (College of Fisheries, University of the Philippines in the Visayas, 1989-09)
    A study was conducted on the effect of common table salt added in waters of different salinity levels used to determine the survival rate, developmental stage, and carapace length of Penaeus monodon larvae from zoea one to post larva one. The following treatments which were adjusted to 33 ppt by adding varying amount of common table salt were: treatment I (8 ppt + 29 g/l) , treatment II (13 ppt + 23 g/l) , treatment III (18 ppt + 17 g/1), treatment IV (23 ppt + 11 g/1), and treatment V (28 ppt + 5/g) . Natural seawater with salinity of 33 ppt was used as control. Certain key ions like Na+, CL-, Ca2+, and Mg2+ were analyzed in each treatment. A sharp drop of. population in all treatments was recorded in the first 5 days of the zoeal stage. Treatment V gave the highest survival rate (25%) , but not significantly higher than treatment IV (20.5%) and control (18%); however, significantly higher than treatment III (10.5%) and treatment II (6.5%) at P<0.05. None of the larvae survived in treatment I after 5 days. Larvae exposed to treatment V had completed post larva one in 11 days (growth index 7). This was not significantly different, however, from those obtained from the control (growth index 6.6) and treatment IV (growth index 6.3). The lowest growth index value which was significantly lower than treatment V was obtained from treatment II and treatment III (growth index 6.0). During the first sampling, carapace length in treatment I reached 0.47 mm, succeeded by the following treatments: III (0.43 mm) , II (0.42 mm) , and V (0.40 mm). Treatment IV and control gave similar results (0.30 mm). After 2 days, rate of increase of CL had shifted from lower to high ionic concentrations culture media. At the end of the study the following carapace lengths were obtained: 1.2 mm for treatment V, 1.15 mm for control, and 1.08 mm for treatment IV. Values obtained from treatment II (0.94 mm) and treatment III (0.98 mm) were significantly lower than treatment V (1.15 mm) . Rearing waters with higher concentrations of K+ and Mg2+ (control, treatments I, and II)showed better growth rate and percent survival than those media with relatively lower concentrations (treatments I, II, and III) . The addition of common table salt to low saline waters, however, did not compensate for the loss of physiologically important ions needed for growth and survival of prawn larvae.