Peter Leithart points out that in the Gospels we often find Jesus eating fish. (Even after his resurrection! See John 21:12.) There was a “Fish Gate” in Jerusalem (apparently the gate through which fishermen brought fish to sell in the city), but we rarely read of people eating fish in the OT.
It is also interesting that in the Old Testament fish were never allowed as a sacrifice and we can’t but wonder why.
There were obviously logistical problems as the river Jordan was some distance from Jerusalem, but there may be some deeper truths here also.
One answer could be that fish are not “domestic”. Only domestic animals were acceptable as sacrifices. Wild animals were never acceptable, even if they were “clean”. A domestic animal was valuable and it was a costly thing to offer it as a sacrifice, but a wild animal did not cost you anything. (A reminder of David’s words that “I will not sacrifice to the LORD…offerings that cost me nothing.” (2 Samuel 24:24)
Another possibility is that the sea often represented the gentiles in scripture (there are many passages in the OT that indicate this). Israel is pictured by the land and the Gentiles by the sea–that which is dangerous, ungovernable, and unpredictable. (In chapter 7 Daniel sees beasts coming out of the sea representing the great gentile empires.)
However, as we know, many of the disciples of Jesus were fishermen, and when Jesus comes eating fish, it is possibly a sign that He is going to use them to bring the Gentiles into the kingdom. This may be pushing it a bit far, but you can’t resist a smile when Leithart says, “Jesus comes to change God’s menu by adding seafood” (by bringing in the gentiles).
Once as a teenager I thumbed a lift on a truck out of Aberdeen (a fishing town in Scotland) and after riding in it all night wondered if I would ever be rid of the smell again (it was not a refrigerated vehicle!). Despite that setback, I still enjoy fish and remain grateful that Jesus seemed to also.