Zinc (Zn) is an essential micronutrient in organisms and an abundant element in the Earth's crust. Trace amounts of Zn released from natural sources can enter aquatic ecosystems through weathering and erosion. Zn accumulates in organisms, and when its intracellular concentration exceeds a certain level, it can induce oxidative stress and trigger oxidative stress-mediated heat shock protein (HSP) modulation. HSP70 is the most evolutionarily conserved among the HSP families. Despite extensive research on HSP70 genes in bivalves, the HSP70 gene family of Tegillarca granosa is still poorly characterized. We identified 65 HSP70 genes belonging to 6 families in the T. granosa genome, with 50 HSPa12 and 11 HSPa B2 genes highly expanded. On chromosome 11, 39 HSP70 (60%) genes were identified, and the HSPa12A genes were highly duplicated. A total of 527 and 538 differentially expressed genes were identified in the gills and mantle based on Zn exposure, respectively. The Gene Ontology of cellular anatomical entities was significantly enriched with upregulated differentially expressed genes in the gills and mantle. Eight of the 11 HSPa B2 genes were upregulated in both tissues. Most of the genes identified in both tissues were involved in "protein homeostasis" and "inhibition of apoptosis," which are associated with the HSP70 family's resistance to extrinsic and intrinsic stress. Hence, this study identified that the HSP70 gene family plays a vital role in the adaptation of aquatic organisms to heavy metal (e.g., Zn) stress in contaminated environments by compiling the different physiological responses to preserve homeostasis.

The objective of this study was to examine gonad development and reproductive cycle of the abalone Haliotis discus hannai at three main abalone aquaculture farms (Uljin, Wando, and Jeju Island) in Korea to obtain information on artificial seed production. The sex ratio (female:male) was approximately 1:1 without significant difference among the three regions or between females and males. Average gonad index was the highest during July in Uljin and Jeju Island and during August in Wando. There was no definitive seasonal change in condition index and meat weight index throughout the year in the three regions. The gonad of H. discus hannai displayed seasonal change histologically, thereby enabling us to distinguish the following stages: inactive (November–December), early active (January–March), late active (March–April), ripe (May–July), spent (August–October), and degenerative (October–November). The main spawning period of H. discus hannai was determined to be during September–October in Uljin an...

Studies on the reproductive cycle, sexual maturation, and spawning of Haliotidae species have been conducted to accumulate data on basic biology, resource management, and culture technology development (Webber & Giese, 1969; Sobhon et al., 1999; Najmudeen & Victor, 2004; Visser-Roux, 2011).

This study was performed to obtain information on the sex ratio, spawning period, and size at sexual maturity for fishery management of the largehead hairtail Trichiurus japonicus in Korean waters. The overall sex ratio (female, F; male, M) was 1:0.46 (n = 1274 females:589 males, 68.4% female) and as fish increased in length, the proportion of females increased. The oocyte development pattern was group-synchronous development, for which oocyte groups at different stages can be identified within the same ovary. The average gonadosomatic index (GSI) showed two peaks in June (3.03) and August (3.10) in females and in May (1.81) and September (2.24) in males. The median value of GSI showed two peaks in May (2.65F, 1.78M) and September (2.55F, 1.87M) for both females and males. As a result of analyzing the GSI and the monthly gonadal developmental stages, the main spawning season was estimated to be bi-annual (May–June and September–October). The anal length of fish at 50% sexual maturity was analyzed using a logistic regression model and was determined to be 16.38 cm (female) and 18.31 cm (male).