We investigated the hemolymph oxygen and acid–base status of akoya pearl oysters, Pinctada fucata martensii, exposed to air for a short time (4 h) to elucidate the acid–base balance and CO_2 dynamics. The hemolymph O_2 partial pressure (Po_2) in air-exposed akoya pearl oysters decreased from 88.7 torr (mean value) to 29.4 torr at 1 h, and the low Po_2 continued for the next 3 h during air exposure. The hemolymph pH decreased from 7.586 to 7.082 during air exposure for 1 h and reached 6.851 at 4 h. The hemolymph CO_2 partial pressure increased from 0.9 torr to 4.4 torr at 1 h and reached 7.3 torr after 4 h of air exposure. The hemolymph bicarbonate concentration and calcium ion concentration at 0 h (control) were 1.9 mM/L and 9.0 mM/L, respectively, and these properties did not significantly change during air exposure. From these results, it was determined that the akoya pearl oysters had hypoxemia caused by hypoventilation at an early phase of the short-term air exposure. The akoya pearl oysters inhibited the discharge of CO_2 by hypoventilation, and respiratory acidosis was caused due to the excessive accumulation of CO_2. Bicarbonate was not mobilized from the shell valve into the hemolymph during the short-term air exposure.

We aimed to clarify the microhabitat preferences of Atyidae shrimps in the middle to upper reaches of the Hiwasa R. , Kitagawatidani R. , and Mugi R. , Tokushima Prefecture, southern central Japan. Relationships between the shrimp abundance and physical environmental variables were surveyed at six sites in 2011 fall and 2012 spring by setting 5-m line transects delineated with ten consecutive 50-cm quadrats along the riverbank. The dominant shrimp species collected from the riverbanks were Caridina multidentata, Paratya compressa and Neocaridina denticulata. C. multidentata was shown to prefer loose boulder or cobble beds with interstices. When interstices were scarce, the shrimps were found inhabiting among the vegetation. P. compressa was shown to prefer vegetation and boulder or cobble bed in pools. N. denticulata tended to prefer vegetation in darker, gently-flowing areas. Our results insist that the three shrimp species segregate microhabitat under base-flow conditions, but flow reduction may cause microhabitat overlap between C. multidentata and P, compressa.

In aquaculture and fixed-net fishing, fishing nets need to be fixed in the water for a long period of time. Therefore, attached organisms such as shellfish, algae, and parasite eggs easily stick to the nets, making periodic cleaning indispensable. A common method is for divers to dive into the water and clean the nets directly with their hands. However, this method is dangerous because it can be fatal to divers due to high water pressure and low water temperature. Therefore, this study considered the possibility of using underwater robot to clean fishery nets in place of divers to avoid these dangers. A mobile mechanism that can move freely along the sides of fixed fishery net in the water has already been developed in this laboratory. In this study, we propose the cleaning system using autonomous robots that automatically cleans aquaculture nets underwater and the charging station using coils for wireless power supply. This robot and a charging station will be installed on the aquaculture nets, and the robot will be driven periodically to clean the nets underwater with less labor and in a safe manner.