不同个体大小和环境因子对瘤背石磺水中耗氧率及皮肤特性的影响

Effect of body size and environmental factors on underwater oxygen consumption rate and skin characteristics of Onchidium struma

本研究设定了3种不同规格,以及温度(15℃、20℃、25℃和30℃)、盐度(5、15、25、35和45)和pH(7.5、7.8、8.1和8.4)3种主要环境因子,通过测定瘤背石磺(Onchidium struma)耗氧率和呼吸器官组织结构的变化研究了其对瘤背石磺呼吸的影响。结果显示,个体较小的瘤背石磺的耗氧率显著高于个体较大的瘤背石磺,且温度、盐度和pH对瘤背石磺的呼吸均有显著影响(P<0.05)。在低于25℃时,瘤背石磺的耗氧率和黏液腺长短径随温度的升高而增大,并在25℃时出现峰值;高于25℃后,耗氧率和黏液腺长短径随之减小;表皮厚度的变化趋势与其相反;每0.1 cm^2皮肤所含颗粒腺数目及长短径变化规律不明显。盐度组各项指标的变化规律或趋势与温度组相似,峰值出现在盐度15。pH实验组中,耗氧率和黏液腺长短径随着pH的增加而增加,表皮厚度和颗粒腺长短径却在减小,每0.1 cm^2皮肤所含颗粒腺数目先增大,在pH 8.1时达到最高值,随后急剧减少。随着时间的增加,各影响因子对瘤背石磺的呼吸强度均减小。由此得出,在水下,环境因子对瘤背石磺皮肤呼吸具有显著影响,在25℃、盐度15和pH 8.1时,呼吸代谢良好;而在15℃、盐度45和pH 7.5时,呼吸代谢受到严重胁迫,这为深入揭示瘤背石磺呼吸机制、物种保护和人工增养殖奠定基础。

Onchidium struma is a shell-less pulmonate and lives in the middle and high intertidal zone. It is con- sidered as a commercially important species owing to its high nutritive value and beneficial effects in Chinese medicine. O. struma is also regarded as an important representative species for a better understanding of the evo- lution from aquatic to terrestrial life since this species has two methods of respiration--epidermal respiration and pulmonary respiration. Epidermal respiration plays an important role in the underwater life stageor stationary stage of O. struma, while pulmonary respiration contributes to its creeping or terrestrial life stage. In the present study, the effect of body size, water temperature （15℃, 20℃, 25℃, and 30℃）, salinity （5, 15, 25, 35, and 45） and pH （7.5, 7.8, 8.1, and 8.4） on underwater oxygen consumption rate （OCR） and epidermal histology was determined to provide valuable information for understanding the respiratory mechanism of O. struma and its evolutionary characteristics. These results demonstrated that smaller O. struma had.higher underwater OCR than larger indi- viduals. Epidermal respiration differed significantly at various temperatures, salinities, and pH values （P〈0.05）. The OCR and the inner and outer diameter of the mucus gland increased as water temperature increased below 25℃. The highest values were observed at 25℃ and then began to decrease gradually at temperature above 25℃. The thickness of the dermis decreased with increasing temperature. The number and the inner and outer diameter of the granular gland did not differ considerably between temperature groups. The differences with respect to sa- linity in dermis thickness and inner and outer diameter of the mucus gland/granular gland were the same as those with respect to temperature. The highest values were observed at salinity 25. The pH also had a significant effect on respiration. The OCR and inner and outer diameter of the mucus gland increased with pH, while dermis thick- ness and inner and outer diameter of the granular gland decreased. The number of granular glands first increased and then decreased; peak values were observed at a pH of 8.1. However, respiration levels decreased with time in all groups. In conclusion, environmental factors such as temperature, salinity, and pH had significant effects on underwater epidermal respiration. Items such as dermis thickness and the inner and outer diameter of the granular gland play more important roles in epidermal respiration in O. struma than the granular gland, which may be key to keeping the body wet and protecting it from invasion or damage from its habitats. O. struma showed optimum respiration metabolism in water at a temperature of 25℃, salinity 25, and pH 8.1. At lower temperature （15℃）, higher salinity （45 psu）, and lower pH （pH 7.5）, this organism will be under considerable stress. This might be related with to the factors associated with its optimal living conditions. The results of this study will provide basic information for the protection and aquaculture of this species and will also be helpful to understand the evolution from aquatic to terrestrial life.