This a Doc (wearing his Didymus hat) puzzle with numbers for words (example a clue giving the length (3,4) to which the answer is "two Jags" would be entered as "2Jags".
18d A lamprey or butterfish (4,5) has only five lights, which I have as ?E?E? which should be a four letter word followed by a five letter number. All the other similar clues are straightforward, but I'm flumoxed by this one. Most gtfl your help. Tks.