Accumulation of copper and zinc in higher concentrations in comparison with other organs is characteristic of the liver, which is associated with exchange - depositing liver function. Gill epithelia in comparison with other integuments of fish has a substantially larger surface area and actively interacts with the external environment, so gills virtually have no protection from the effects of different substances present in water including metals.

These are basically the main sites of deposition due to their cellular configuration.

It is interesting question. Be it heavy metal or other toxic substance, liver is the main organ for a job assigned to detoxify or metabolize to make it polar (water soluble) thus can easily be excreted through kidney. 

Answers with evidence from research papers will be helpful.

The gills are in direct contact with water and their metal content can have a direct relationship with water metal concentration (Legorburu et al., Environ. Techno. Letters, 9, 1373). In case of fish-kills because industrial industrial effluents high levels of metals can be detected in gills (Legorburu and Canton, Toxic. Environ. Chem, 23, 161).

Metal concentration in muscle tissue usually shows some difference when the metal concentration in water is high, but is not considered as an accumulating organ (Sanchez et al., Water, Air, Soil Pollut., 107, 303).

Dear Inigo Legorburu, I appreciate your answer but in order to get more details about it, Please attach links of the research papers whose reference you have mentioned.

You can found them in my Research Gate profil.

Accumulation of copper and zinc in higher concentrations in comparison with other organs is characteristic of the liver, which is associated with exchange - depositing liver function. Gill epithelia in comparison with other integuments of fish has a substantially larger surface area and actively interacts with the external environment, so gills virtually have no protection from the effects of different substances present in water including metals.

Yes dear Aiman Konkabaeva. But what about Liver that in some cases liver has-been reported to contain more heavy metals than gills.

It is believed that in the intact liver cells along with the stress proteins, there are proteins having different binding ability with respect to exogenous molecules (metal ions), and these proteins form specific intracellular the pattern of distribution of metal ions, which ultimately provides the biological effects of metals

Hello.

Gills are in direct contact with the water and if the water is contaminated this will be the main route for the contaminants to enter the fish body. Then with the blood flow (gills are highly vascularised) they can reach other internal organs and tissues. On the other hand, if the food, which the fish ingest is contaminated the digestive system will be the main route for the contaminants to reach other organs such as the liver, kidney and spleen, which are haematopoietic organs.  Liver is the main site for toxicant bioaccumulation, storage and detoxification, and kidney is the main organ for toxicant excretion.  Toxicant accumulation in the internal organs is associated not only with important function such as haematopoiesis, antioxidant defense, detoxification, and excretion, but also with metallothionein synthesis. In terms of muscles,  it is well

known that the muscles do not actively accumulate metals and seems to have a very fast decontamination rate. However, the muscles are the main site where POPs (persistent organic pollutants such as pesticides, PAHs, PCBs, etc.) accumulate the most. Therefore, these tissues are used in studies regarding human health and food poisoning.

Article Metal bioaccumulation in common carp and rudd from the Topol...

Thank you very much dear Vasela Yancheva for your valuable comment and article. As you mentioned that muscles are not active in accumulating heavy metals due to high decontamination rate, do you have any reference for it. Furthermore on the other hand they can accumulate pesticides and Poly nuclear aromatic compounds etc. Any scientific reason for this phenomenon.

Because gill is one of the direct entrance of heavy metals which run into the blood stream during its accumulation cycle and stay a long time in the liver whcih called chemical chamber of  all aquatic animals. 

Heavy metals tend to be more prevalent in organs of fish with a higher concentration of fatty tissue. You may want to take a look at this paper for specifics on deposition of heavy metals in the different fish organs. 

http://link.springer.com/article/10.1007/BF03326011

Dear Amanda Peters. I agree with your viewpoint but to be more clear i want to go through the paper and unfortunately  i don't have full access to this link from here. You  please attach it here, if you don't mind.

This link should let you access the paper without a subscription.

https://tspace.library.utoronto.ca/bitstream/1807/62553/1/st08021.pdf

Thank you dear Amanda Peters for this favour.

dear Mohammad,

I'm enclosing a study about metals distribution in  a freshwater fish organs (Silurus glanis) from Italian rivers, hoping it will be helpful.

We found that  metals were differently distributed in the various organs, the highest concentrations of Hg were found in muscle and liver, Cd in kidney, Pb in gill and liver, As in muscle, and of Cr in gill and liver...

kind regards

stefania

Thank you all for sharing because I had the same question. Why more accumulation in the gills, liver than in muscles

Interesting.... Following

I just found all the answers I needed. Thanks to all the contributors

We recorded same findings in both fish (mud-skippers) and amphibians (frogs) in Port Harcourt. Metal concentrations were lower in muscle tissues than in gill /lungs, liver and intestine. Thanks to all contributors.

Thanks to all, I found all answers .