This may mean some earlier obs. of 'herring fry' will need revising.
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Good fish key here shared by Francis Parfrement on facebook. It shows the difference in the orientation of the dorsal and pelvic fins described above, ie Sprats have pelvic fins in front of the origin of the dorsal fin, and herring vice versa.
Lat/Lng: 55.0435, -5.9635
OS grid ref: NW468792