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Study on Early Developmental Stages of Donkey Ear Abalone, Haliotis Asinina Linnaeus, 1758
Abstract:
This study was conducted to determine the optimal salinity and temperature suitable for Haliotis asinina during the early embryonic and post-embryonic developmental stages. Factorial completely randomized design was used in the experiment. The study was conducted by stoking fertilized eggs and newly hatched larvae in four levels of temperature (23, 26, 29 and 32°C + 0.05°C) and four levels of salinity (25, 30, 35 and 40 ppt). The effect on the duration of development, hatching time, hatching rate, survival rate of larvae, and larval size was evaluated.
The eggs that were spawned and fertilized at 29°C and salinity 30 ppt were directly stocked at the different combination of temperature and salinity without acclimatization. No impairment of embryos manifested when the level of salinity was changed from 30 ppt to either 25 ppt or 35 ppt and when the temperature was directly changed from 29°C to either 26°C or 23°C. However, it was detrimental when salinity changed to 40 ppt or when the temperature was increased to 32°C. Changing both salinity and temperature at certain levels showed better response than those kept at stable salinity and temperature during spawning or fertilization.
Increasing temperature up to 29°C or the salinity up to 35 ppt shortened the duration of embryonic development. Seventy-five to 80 percent of fertilized eggs developed only until 2-cell stage when incubated at 32°C or 40 ppt.
Combination of 29°C and 35 ppt showed faster hatching time (301 minutes) than those incubated at 29°C and 30 ppt (326 minutes) (p < .01). But the hatching time was significantly lower (p < .01) at 29°C with lower salinity 25 ppt (436 minutes) than those at lower temperature (26°C) with higher salinity (35 ppt).
All eggs incubated at higher salinity developed and hatched faster than those stocked at lower salinity in every level of temperature.
Hatching rate of H. asinina trocophore was the highest at combination of temperature 29°C and salinity 35 ppt (78.4%). There was significant difference (p < .05) found in incubating fertilized eggs at different salinity and temperature combination.
Survival rate of larvae H. asinina until creeping stage ranged from 0 to 11.8 percent. Survival rate (11.8%) at 26°C and salinity 35 ppt was significantly higher (p < .05) than those reared at 23°C and salinity 35 ppt (6.53%). When temperature was kept constant at both 23°C and 26°C with salinity 35 ppt, the survival rate was significantly higher (p < .05) than those at the same temperature but at lower salinities of 30 ppt and 25 ppt.
The newly-hatched trocophores were found only at combination of temperatures (23, 26 and 29°C) and salinities (25, 30 and 35 ppt) with mean sizes of 161+ 1.154 – 162.3+ 0.577μm x 125.83±0.28 – 127.17±0.288μm). The size of newly-hatched trocophore in all treatments was not significantly different (p < .05).
The larvae kept at temperature 26°C both at salinity 30 ppt and 35 ppt had the biggest size, with the mean of 283.3±12.9 x 166.67±25.8 μm and 283.93±12.7 x 217.23±8.01μm, respectively. The larvae kept at 29°C were bigger than those at 23°C and salinity 30 ppt and 35 ppt.
The best temperature-salinity combination in terms of hatching time and hatching rate was 29°C and 35 ppt. The best for larval survival up to creeping stage was at 26°C and 35 ppt. The optimum temperature of newly fertilized eggs up to hatching was 29°C, but from hatching to creeping stage the optimal temperature was 26°C. The best salinity for all stages was 35 ppt.