Conc in wet weight = ((100 - % of water)/100)* Conc in dry weight

Thank you Cyrus

Anand,

The wet to dry weight ratio for fish is in this range you mentioned (4 - 6).  For juvenile salmon I usually get about 4.5.  For many species of larval fish species, the ratio can be much higher.  I've seen values of 6.4 up to approximately 10 (= 90% moisture).  Each species, and individual fish, will exhibit different values that is a function of many factors such as lipid content, reproductive state, and their overall health.  It's best to have data for the species you are working with to be sure.

I concur with the answer by Dr. Meador. However, from a practical point of view (that is for reporting  aims) and if you forgot to measure mass loss after drying, the factor  you mention in your original question is close enough for the muscle of edible fish species which on average have  a moisture content close to 75-80%. Applying then the equation by Cyrus (100-80)/100=0.2 or (100-75)/100=0.25.

As an example, if your fish has 8 ppt of the offending metal (dw), the wet weight will be between 1.6 (8 x 0.2) and 2 (8 x 0.25) ppt (that is, you divide by 4 or by 5). It helps if you look in the literature for the moisture content of species with similar characteristics or taxonomically close) 

Thank you, Dr. Domenico and Dr. James for your valuable suggestions. 

We've just published a paper documenting these factors in a set of fish species. It is not in the same environment as in your work, but you may find some useful information

Hope it helps !

http://dx.doi.org/10.1016/j.marpolbul.2017.08.046

wet weight = 1 - dry weight i.e. if wet weight is 100 g and dry weight is 10 g the moisture is 90 % and so divide the number based on dry weight analysis by 10 another example if substance present as 1 mg / g dry weight and moisture % was 90 % the content of this substance will be 0.1 mg / g weight weight

For snail and mussels we use a conversion factor of 0.24 and 020 C.obtusa and and A.granosa respectively. (Yap and Al- Mutairi, 2022)