Total amount of cholesterol in European yellow and silver eel swimbladder gas gland tissue (μg mg⁻¹). For comparison, yellow eel muscle tissue has also been analysed. n = 5 for muscle tissue and yellow eel swimbladder; n = 6 for silver eel swimbladder tissue; mean ± s.d.; different small letters indicate significant differences between samples (P < 0.05)

Agarose gel electrophoresis (2%) of RT‐PCR (real‐time PCR) reactions of cDNAs produced from total RNA samples from various tissues of a yellow American eel (Anguilla rostrata). Genes amplified were Aquaporin 1 (aqp1aa, aqp1ab) and two housekeeping genes, glyceraldehyde 3‐phosphate dehydrogenase (gapdh; accession no. AB07521) and beta 1 actin (accession no. GU001950)

Western blot of crude membrane extract proteins from the rectum of yellow American eels (Anguilla rostrata) using the custom affinity–purified polyclonal eel Aqp1aa and Aqp1ab antibody; 300 μg of protein was used. Sizes of the precision plus kaleidoscope prestained protein size marker (Biorad, Hercules, CA, USA) are as indicated in kilodaltons (kDa)

Immunohistochemical staining of (a) Aqp1aa and (b) Aqp1ab in swimbladder gas gland tissue from European eel Anguilla anguilla. Both antibodies revealed positive staining, whereas (c) no background staining was observed in the negative control. Scale bars are 50, 100 or 200 μm, respectively. b: blood vessel; gg: gas gland cell; L: swimbladder lumen

Immunohistochemical staining of (a) Aqp1aa and (b) Aqp1ab in swimbladder gas gland tissue from Anguilla anguilla at higher magnification. Positive staining of (a) Aqp1aa was detected in endothelial cells, whereas (b) Aqp1ab staining was prominent in apical regions of gas gland cells. Scale bars are 50 or 20 μm, respectively. b: blood vessel; gg: gas gland cell; L: swimbladder lumen