Water and fish are huge themes in the Bible. Right back there in Genesis they start.
There is something valuable in the fish as it appears in the Bible. If you needed a clue that we can find something of value in the fish just notice that Jesus told his disciples to go and get coins from the mouths of some fish.
He made it clear that the particular value in those specific fish was of no consequence and He was only paying lip service (my weak joke) to the tax so as not to offend. That was quite a pointed subtlety because of course the true value in the fish is not earthly gold, for as Jesus essentially indicates, He already owns the whole universe so has no need of gold. The lesson is that the value in these fish represents the souls in the men that the fishers of men will catch, that will be given over to the Lord as the tax is given over to the earthly authorities.
The pre-Christian fish symbol (of female genitalia – turn sideways nose up (my rude!) to see (yes it’s a deeply rude but funny semiotic joke that I do get – I wonder who first told it? Umberto Eco I think would have got along with that guy) – was appropriated and renamed as the acronymic form of ichthus and used as a symbol by the early underground church.
Scratching the fish on a wall as graffiti was a religious-political act of rebellion against Rome that could probably get you killed if they found you doing it.
Making the sign of the fish by crossing fingers was a way the Christian rebels could recognize each other silently and recite the assertion that ichthus represents.
The crossed fingers also echo the cross where He died to save us, so if you do cross your fingers “for luck” think not of luck for there is no such thing as luck, but think of our Lord by acknowledging what the ichthus means, say your hope in a prayer and thank the Lord for all the Christian martyrs who gave and continue to give their lives in His service.
No such thing as luck? Indeed no. Luck would require chance which would require some underlying true randomness. True randomness cannot be created mathematically. Every ‘random” number or event is really just pseudorandom. God did not make an unplanned universe and it does not allow random. Random would have to be demonstrable and to do that it would have to match a rule and to do that it would have to defeat its own nature philosophically and logically. Random is an oxymoron and cannot exist. That’s one deep objection to a spontaneous Godless Universe by the way but I’ll leave instrumentalism to another day.
In Jonah’s tale we see a fish swallows a man who is not doing God’s will then it spits him out and the man then does decide to do God’s will. The fish (Christianity) swallows you then upon baptism you are pulled from the water like a fish (Jesus makes fishers of men) ready to do God’s will. You are washed clean and filled with the living water, ready.
Habbakuk says evil catches men like fish but God reminds him they are storing up trouble, The Devil’s fishing will not bring you anything even as useful as a few small coins in the long run. Better to fish as Jesus teaches, on the other side of the boat.
If you graffiti a fish on a wall, you of course then walk away from it. There is a little symbolism you might like to think of in that act. In walking away from the fish you have graffitied, you echo the footsteps if the disciple who left the abundance of fish (that Jesus had helped him catch) on the quayside to go follow Jesus instead.
So when you see a fish in the Bible, remember the fisherman who put it there is subtle, look deep into it for value, and make sure you catch on to what He is telling you, and if you see a real modern ichthus graffiti on a wall, praise the Lord for His message of rebellion against evil still lives in the hearts of His Church.