An assay of optimal cytochrome c oxidase activity in fish gills.

Cytochrome c oxidase (COX) catalyzes the terminal oxidation reaction in the electron transport chain (ETC) of aerobic respiratory systems. COX activity is an important indicator for the evaluation of energy production by aerobic respiration in various tissues. On the basis of the respiratory characteristics of muscle, we established an optimal method for the measurement of maximal COX activity. To validate the measurement of cytochrome c absorbance, different ionic buffer concentrations and tissue homogenate protein concentrations were used to investigate COX activity. The results showed that optimal COX activity is achieved when using 50-100 µg fish gill homogenate in conjunction with 75-100 mM potassium phosphate buffer. Furthermore, we compared branchial COX activities among three species of euryhaline teleost (Chanos chanos, Oreochromis mossambicus, and Oryzias dancena) to investigate differences in aerobic respiration of osmoregulatory organs. COX activities in the gills of these three euryhaline species were compared with COX subunit 4 (COX4) protein levels. COX4 protein abundance and COX activity patterns in the three species occurring in environments with various salinities increased when fish encountered salinity challenges. This COX activity assay therefore provides an effective and accurate means of assessing aerobic metabolism in fish.

Microplastic ingestion by adult milkfish Chanos chanos (Forsskål, 1775) in aquaculture system: The case of Butuan Bay, Philippines.

The Philippines is an archipelago that relies on marine resources. Butuan Bay in the Philippines supports aquaculture, which can contribute to and can be impacted by plastic pollution. However, the microplastics (MP) in milkfish, an important aquaculture species in the area, are yet to be ascertained. This study determined the prevalence of microplastics in the surrounding seawater and in the gut of adult milkfish from cages in Butuan and Nasipit in Butuan Bay. Water samples in Nasipit and Butuan contain 0.20 items/L and 1.00 items/L, respectively. MPs in milkfish in Butuan (10.27 items/individual) were significantly higher than in Nasipit (5.40 items/individual). A total of 235 MPs in 29 out of 30 fish samples (97 %) from the two sites were detected. The dominant MP shape and color were fiber and blue, respectively. The presence of microplastics in the milkfish may indicate a possible risk to the fish species and human health.