Characteristics of the feeding behavior and relationship between the standard length (SL) and the size of scrape marks of ayu Plecoglossus altivelis altivelis were studied using 123 cultured specimens in aquaria. Feeding behavior was observed individually, 116 specimens (94%) have mouth laterality for feeding. Also, feeding behavior were found two types. The first was eating the algae directly from the shelter in 91 specimens (78%). The second left the shelter and ate the algae after changing direction back to the shelter (22%). One side of the lower jaw when feeding on the acrylic plate side was turned downward and the other side of the jaws was closing. On the scrape marks, 11 to 14 and 11 to 13 level lines were visible caused by the upper and lower jaws and the algae was not scraped between the upper and lower parts. The comb–like teeth groups are arranged as 13 to 14 rows and 12 to 14 rows on the upper and lower jaws, respectively. Therefore, it is suggested that they use almost all of the comb–like teeth groups except the back teeth row on the upper and lower jaws for feeding. The lengths of upper and lower jaws were found to have power regression with the SL, respectively. Also, the relationship between the SL and full width of the scrape marks (FWSM) was： FWSM = 0.3939SL^0.6767 (R^2= 0.8392, 64-212 mm SL).

We investigated the hemolymph CO_2 partial pressure (Pco_2) and bicarbonate concentration ([HCO_3^–]) of the acid–base balance of Mytilus coruscus under resting conditions. Hemolymph collected from the adductor muscle was subjected to the following measurements. Mean values for hemolymph pH and total CO_2 concentration for this state between 18℃ and 23℃ were 7.568-7.601 and 1.54-1.59 mM/L, respectively. Hemolymph Pco_2 and [HCO_3^–] were calculated using the hemolymph pKapp estimated using the relational expression with temperature. Hemolymph Pco_2 and [HCO_3^–] were 1.77-1.83 torr and 1.47-1.50 mM/L at 18℃ and 23℃. To verify Pco_2 and [HCO_3^–], the values were calculated using pKapp obtained by in vitro method (tonometry). Despite the different determination methods, no statistical difference in the obtained values of Pco_2 and [HCO_3^–] were observed. Non-bicarbonate buffer values (ꞵ_NB), which were calculated using the slope of the relational expression between pH and [HCO_3^–] in hemolymph, were 0.42 slykes at 18℃, and 0.54 slykes at 23℃. The hemolymph ꞵ_NB of M. coruscus was in the range of other bivalves, and the hemolymph buffer capacity of the non-bicarbonate buffer system would reflect the Mitilid species.

Identification of leukocytes on tissue sections is important to elucidate the mechanism of swim bladder lesions. To determine the best fixative solution for a koi carp swim bladder, the swim bladders were fixed in 10% formalin, Bouin's, MFAA and Davidson's solution. The swim bladders fixed in MFAA or Davidson's solution were severely detached and twisted, whereas those fixed in 10% formalin and Bouin's solution kept their external shape. However, the majority of the 10% formalin-fixed specimens showed detachment of the tunica interna from the tunica externa under the light microscope. Therefore, Bouin’s solution was determined to be the most suitable fixing solution for the swim bladder. Imprints (head kidney-touched slides glass were fixed with Bouin's solution) and tissue sections of head kidney fixed in Bouin’s solution were stained with Mayer’s hematoxylin and eosin (HE) and May-Grünwald·Giemsa (MGG), and the best staining method for leukocytes identification was investigated. In the HE-stained specimens, identification of leukocytes by staining was difficult. On the other hand, MGG-stained specimens could be identified by staining. Fixation with Bouin's solution and MGG staining was determined to be the most suitable method for leukocytes identification in the swim bladder.