Hi! I'm attaching here a picture of fishes which I purchased today. While cutting and washing I found the water color as blue. Please someone here confirm me whether the color is natural I mean from fish or was added anything. The fish is like ribbon but not too much thin.

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WP_20151204_18_34_52_Pro.jpg, 1.51 mb, 2592 x 1456

Nearly all fish have red blood (as in mammals) due to the haemoglobin. Some invertebrates use hameocyanin instead to transport oxygen in teh blood and this gives it a blue colour.

That said, blue/green blood is reported from a some marine fish species. From your photo it is difficult to hazard an idnetification here since key features (heads, tails, overall body shape) are not visible. It would also be helpful to know where in the world you are and what common name (if any) the fish were being sold under.

Some members of the wrasse group (Labridae) have blue/green blood but this is not a wrasse! I have seen an old description of the Japanese eel (Anguilla japonica) having blue blood (but someone may have a better source of info on this). This is a widely farmed species so is readily available in fish marked in much of Asia and has a similar body shape to the picture above but I cannot be sure.