Fish before on best lake (8)

I haven't cracked this one yet — but the brilliant team at Times for the Times have:

PICK (best), ERE (before}, L (lake). A young pike. This has appeared only once before in the TfTT era and that was in 2009, so I wonder if it may cause some problems, especially as speed merchants may be tempted by ‘mackerel’ unless they already have the crucial P-checker in place. Fortunately I did, but I happened to know the word anyway as I had a pal at prep school back in the 1950s with this as his surname and its meaning came up.