“Keep in mind that the braisa was trying to describe a chilazon. If one was asked describing the murex trunculus, saying that it is the color of the ocean is a very poor description.”
Well, being that the chilazon dies once it is out of the water for a short time whenever you will find a chilazon that you can use it will be domeh lyam. Hence the siman is a very good siman.
About fish being domeh ldag. Let us make a hanacha that the chilazon is a snail*. If so the shape of one snail will be more ‘domeh ldag’ than the other snails. Now I request permission of the moderators to allow the following link to show my point. Please see page 58 of the following pdf file for some pictures http://www.tchelet-net.022.co.il/BRPortalStorage/a/31/86/54-EnqP9QK36s.pdf
What I intended with the radvaz is to show that coming up every 7 years is derech nes and after the churban that stopped happening. This is his lashon ???? ???? ????? ?? ??? ???? see his full lashon in siman ???”?
* ( I can make an arichus out of this with many rayos but for this point and maybe I will do so later. but this is the hanacha of many achronim
??????? ??? ????: ????”? (???’ ?????? ?’ ????? ???”?), ????”? ??? (??? ????”?, ???’ ?? ???? ????? ??”?), ?????? ????? (?????? ???? ????), ??????? ???? (?”? ?”?), ??????? ????? ???? ???? (?????? ???