FreshFish - Welcome!
As far as keeping herring - if you mean freezing it for use of the season, here's what I do -
Short of having a vacuum packing thingy.......
As soon as I get my take.....where I go it's 40 or 48 a week, forget which, but basically, as thick as they were last year, two net fulls in the cooler would get ya about 60, and the officer there would say "Yep, that looks okay" (No worries gents, I only did that twice last year during the run season, so I'm not greedy...)....anyway, get them in the cooler, ice them down (some guys add salt to the ice, but I don't) and get them home ASAP.....but in a cooler they will be all but dead in a 1/2 hour or so.....
I dump them all in my sink in the basement. I then sort them into gallon ziplock bags, 3 or 4 per bag, depending on the size. Once they are all in the bags, I fill the sink with water. Seal all but the very corner of the bag, and slowly and carefully submerge the bag in the water, keeping the open corner above the water line. This forces all the air out of the bag, almost as well as a vacuum packer. Once you get up to the corner, seal the bag the rest of the way, and toss it aside. Continue until all the bags are done and sealed.
Then, fold them up nice and neat, and place them in the freezer. Depending on how many I have, and how much freezer space I have (I have a fridge in the basement for exclusive bait and beer use.....

), I might only put 5 or 6 packs in at a time, so that I don't have to layer them. If so, the rest go in the fridge in the interim. This allows them to freeze rather qucikly. Once the first batch is frozen, I put in the next batch on top, etc. until all are in there.
Keeps them nice and fresh with no freezer burn for most of, if not the whole season.
BTW - use the same method if you are freezing eating fillets.....I have bluefish caught in November that were frozen that way. Had some on the grill a week ago, and while not QUITE like fresh caught, they were still tasty.....
