I'd second the fact it's a Goby....My normal tell tale would be the dorsal fin, Gobies have 2 distinct dorsal fins whereas Blennies have a continuous one. But this isn't clear from the pics provided. However, as far as I can make out from the pic, the fish only has 1 pelvic fin . Gobies have their pelvic fins fused into one to allow them to effectively use it like a sucker and stick to rocks where Blennies have 2 separate pelvic fins.
I found that the best way to photo small fish is in a glass container full of water as you can see the fins better,I got about 10 small gobies one day for the aquarium and I thought they were all sand gobies but when I looked at them swimming I could see the different marking on the fins
I had sand gobies,common gobies,painted gobies and a leopard spotted goby most looked the same out of water
lifetime species fishing and rock pool
1 dogfish,2 whiting,3 flounder,4 two spot goby,5 mackerel,6 pollack,7 common blenny,8 European eel,9 butterfish,10 Deep-snouted pipefish,11 rock goby,12 poor cod,13 corkwing wrasse,14 coalfish,15 turbot,16 tompot blenny,17 dab,18 dragonet,19 shorerockling,20 thornback ray,21 three bearded rockling,22 sandeel,23 grey gurnard,24 sea scorpion,25 scad,26 plaice,27 ballen wrasse,28 bullhuss,29 conger eel,30 blue shark,31 blonde ray,32 cod,33 pouting,34 topknot,35 Fifteen-spine Stickleback,36 mullet,37 Sand Goby,38 Montagu's Blenny,39 Three-spined Stickleback,40 goldshinny wrasse,41 painted goby,42 five bearded rockling,43 Sand-Smelt,44 Small-headed Clingfish ,45 sole
Gobies species have different Adult sizes, some bigger (and smaller) than the Blenny/Shanny (Lipophrys pholis) Max size 16cm
Common goby (Pomatoschistus microps) Max size 6cm.
Rock goby (Gobius paganellus) Max size 12cm.
Black goby (Gobius niger) Max size 17cm.
Giant goby (Gobius cobitis) Max size 27cm.
Two spotted goby (Gobiusculus flavescens) Max size 6cm.
Good tip from gfkelly1969 on using a glass container to help with fish id.