Quantitative assessment of egg maturation in the horse clam Tresus keenae (Kuroda & Habae 1950) from the south coast of Korea using indirect enzyme-linked immunosorbent assay (ELISA)

The quantity of eggs produced in an annual reproductive cycle of some commercially important shellfish is vital in a hatchery operation or managing the wild populations. The horse clam Tresus keenae (Kuroda & Habe, 1950) is one of the aquaculture candidate bivalve species occurring on the subtidal soft bottom of the coastal Northwest Pacific ocean, while their reproductive effort is yet to be determined. Unlike fishes, assessing the reproductive effort of a marine bivalve is challenging since most species do not have a separable gonad except scallops, as ovaries or testis are inseparable from the visceral mass. Therefore, we developed an indirect enzyme-linked immunosorbent assay (ELISA) to measure the quantity of the egg produced in an annual reproductive cycle. The rabbit anti-egg protein IgG developed in this study was sensitive enough to detect as little as 0.3 mu g/ml of the egg protein in indirect ELISA. The horse clam produced as much as 41.1% of the total body weight as eggs during spawning in October, equivalent to 378.2 million mature eggs. Histology revealed that T. keenae has a short resting period in January and February and a long period of gonial mitosis from March to August. The annual reproductive cycle and reproductive capacity of T. keenae estimated in this study provide crucial information in the successful hatchery operation to develop the horse clam aquaculture and manage the wild population for sustainable exploitation.