With their huge ‘armour-plated.’ heads, raised, bulbous eyes and tapering bodies, the gurnards are odd-looking fellows, though easily identifiable. It is not so easy, however, to distinguish between the six different species found in British waters. The piper is a deep-water fish living at depths of at least 300m (985ft), while the long-finned gurnard is rare. The remaining four species – tub, red, grey and streaked gurnards – are more abundant.
The tub gurnard is the most common. It is large, being the only one of the six species to weigh in at more than 4/4 lbs (2kg). Colour is important too – in the tub the pectoral fins can be either blue or green, edged with either red or bright peacock blue (when the fins are spread out these colours are uppermost). In other gurnards these fins are not nearly so well developed nor so brightly coloured.
No-one is certain what the brilliant pectoral fins are for – but they are probably used either as a defence mechanism to deter predators or for attracting a mating partner. Many other animals have bright colours which can suddenly be revealed to startle an oncoming predator. They also make the creature seem much larger than it really is. The degree to which bright colouring is developed in the tub is perhaps a response to its rather solitary life-style.
Its body colouring is variable and can range from red/pink (making it easy to confuse with the red gurnard) to yellow and brown. Its eye tends to be smaller than that of either the red or grey gurnard and its lateral line scales are small and smooth (not large and spiny as in the grey).
The tub lives on muddy or sandy bottoms at depths of up to 50m (165ft). Common around Britain, it is more widely dispersed than either the red or grey gurnard. In parts of the North Sea grey gurnards are caught in their hundreds, and in western parts of the English Channel the same is true of red gurnards; but in both areas the tub is only caught in ones and twos, preferring a more solitary life-style than that of its cousins. Being a larger fish, the tub can afford to spread out, while smaller species form schools for protection.
Feeling for food
The gurnard has a unique way of searching for food – its pectoral fins are so well developed that the first three rays have become separate feelers which are covered in sensitive taste buds. It uses these finger-like rays to ‘walk’ along the sea bed probing for crabs, shrimps and bottom-living fish such as gobies, sandeels and young flatfish. The tub is a fast swimmer so it can catch sand smelts and pilchards.
The gurnard reaches sexual maturity after three years, and moves to shallow waters between spring and early summer to spawn. The eggs hatch after about ten days and the larvae feed on plankton until they are big enough for life on the sea bed.