Rapid development has been associated with mercury pollution in the aquatic environment, leading to mercury toxicity in fish and other aquatic organisms. Histopathological abnormalities such as hyperplasia, inflammation, and necrosis have been observed in various fish tissues as a result of mercury contamination based on organic mercury (methylmercury) and inorganic mercury (mercuric chloride) exposure via dietary or water exposure, respectively, with different duration doses of mercury. Knowing that tissue changes occurred at an important part of each organ that played various critical roles in the normal physiological actions of fish, it is critical to understand how fish respond to mercury contamination and how this heavy metal element affects their general well-being. This review paper focuses on major tissue histopathology changes in response to mercury toxicity and their potential use as a mercury contamination indicator in fish.

Increasing human-induced climate issues, such as water pollution, have triggered rapid physiochemical changes, especially in coastal regions. These changes have directly impacted aquatic animals that live near coastal areas, such as bivalves and crustaceans (e.g., clams, crabs), as well as those that live in the lower areas of the habitat (i.e., sediment). Heavy metal pollution (e.g., mercury) is one of the most concerning physiochemical changes in these areas. The effects of heavy metals on coastal environments and organisms can be substantial, in spite of restoration efforts. Thus, more studies are needed to analyze the current situation of the impacts of climate-change-related issues on heavy metal concentrations in coastal areas. In this paper, we provide a scientometrics analysis of the interactions between climate change and heavy metal concentrations in coastal regions around the world. Scientometrics is the quantitative analysis of the available literature, with a focus on research patterns, using continuous and systematic methods. Our results showed that there was a total of 7922 related studies from 1979 to 2021. Heavy metal contamination, ecological quality status and ocean acidification are among the most influential keywords in this field. We concluded that among climate change issues, heavy metals are becoming a popular topic within research associated with climate change.

Highlight ResearchThe reproductive characteristics of L. hoevenii were examinedThe potentially smallest maturity sizes of female and male L. hoevenii were 350 g and 180 g, respectivelyThe fecundity of a 1,000 g L. hoevenii can be more than 100,000 eggsL. hoevenii was determined as a multiple spawnerAbstractSultan fish (Leptobarbus hoevenii) is a high value freshwater fish, cultured in some Southeast Asian countries, including Malaysia and Thailand. However, information on its reproductive characteristics is very scarce. This study examined the gonadosomatic index (GSI), fecundity, egg diameter, and determined whether L. hoevenii is a single- or multiple-spawner. Twenty male and female pond-farmed L. hoevenii broodstock were obtained to measure their total length (TL), body weight (BW) and gonad weight to calculate the GSI. Ten females were randomly sampled from the 20 to determine their fecundity. A total of 1,500 eggs were sampled from each female. The egg diameter was measured then its frequency distribution was analyzed to detect the number of egg class group, and to determine whether L. hoevenii is a single- or multiple spawner. The female L. hoevenii examined were 32.2-47.1 cm and 350-1,200 g, while the males were 30.7-45.8 cm and 180-970 g in TL and BW, respectively. All female specimens contained gonads. The potentially smallest mature samples were recorded at 350 g (female) and 180 g (male). GSI for the female and male L. hoevenii were 1.81-12.28 % and 1.03-5.09 %, respectively. The fecundity was 35,467 -128,067 eggs, while the highest fecundity was observed in a 1,000 g fish. The observed egg diameter ranged from 500 to 1,855 μm. Two to five groups of egg class were detected, indicating that L. hoevenii is a multiple spawner.