Invasive Species Compendium

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Abstract

Hepatic metallothionein and metal (Zn, Cu and Cd) variability in relation to reproductive cycle of Mullus barbatus and Merluccius merluccius from the Eastern Adriatic Sea.

Abstract

The present study compares metallothionein (MT) and metal (Zn, Cu, Cd) variations in liver cytosol of feral fish Mullus barbatus and Merluccius merluccius as a function of fish reproductive cycle. The fish were sampled in the spawning (Merluccius merluccius, European hake), as well as pre- and post-spawning period (Mullus barbatus, red mullet) in the Eastern Adriatic Sea to observe inter-species and natural physiological variations. In both species, average mass concentrations of essential metals (Cu and Zn) are 40 to 300 times higher than that of toxic Cd. Zinc represents the predominant metal in liver cytosol of both species. Metallothionein, Zn and Cu are significantly increased in fish sampled before and during the spawning. Hepatic MT, Zn and Cu levels of M. barbatus sampled before the spawning are 2.2; 7.2; 1.7 times higher than in the period after the spawning, respectively. Toxic Cd does not reflect endogenous processes but is related to fish size. Metallothioneins are significantly positively correlated with Zn (r2=0.71) in M. barbatus during pre-spawning season, while toxic Cd is negatively correlated (r2=-0.72). Liver mass and hepatosomatic index also show seasonal variability, with statistically significantly higher levels in the pre-spawning and spawning period. Hepatosomatic index amounts 2.35-3.78% before and during the spawning, and 1.35% after the spawning. Moreover, during the spawning and pre-spawning season, MT and Zn follow the changes of hepatosomatic index in both species, indicating the period when essential metal and MT levels are affected by fish physiology. For biomonitoring purposes, fish should be sampled during the post-spawning period in order to minimize the influence of the reproductive cycle.