the adjacent water

The Observer's Book of Freshwater Fishes of the British Isles, by A. Lawrence Wells (Frederick Warne & Co., 1941). 

The whole book is fascinating and very readable; it brought home to me how little contact I've had with fish, since those youthful days of pike and perch fishing in Jämtland. Even back then, I was often more interested in the waterside plants and left it to others to catch our dinner. According to the book there's a theory that pike and perch coexist so often because the perch's spined dorsal fin makes it unpalatable to the pike.

Much of what's written here is probably out of date. For instance, the Burbot is described as "extremely local"; it's now regarded as almost extinct in the British Isles. (A book in 1590 had described the Burbot as so common that it was fed to hogs.)

Here's a few extracts that caught my eye.

The Brook or Planer's Lamprey.

Both this and the Lampern [small lampreys] are now chiefly captured for bait, forming, in many of our rivers, quite profitable industries. Cod are very partial to a piece of lamprey. At one time they were greatly in demand for the table and "lamprey pie" was held in high esteem. ... Unfortunately this fish is somewhat indigestible and Henry I is said to have died from a surfeit of them ... A good recipe for cooking lampreys is the following which comes from Worcestershire : Clean the lampreys thoroughly by rinsing well with salt and water ; then gently rub a little mixed white spice over them and leave for twenty-four hours. Quite a lot of fluid will ooze out, but do not throw it away ; this will be put in the saucepan with them to stew. If this fluid does not completely cover the lampreys, unseasoned beef gravy may be added when they are nearly done. A glass of port wine added at this stage is also advocated. 

The Salmon.

Gradually the parr marks disappear and when they do the salmon is then referred to as a "Smolt". In mid-spring, usually about May, the smolts assume a silvery appearance and then take it into their heads to visit the sea, and when they arrive there they develop a tremendous appetite. Fortunately plenty of food awaits them in the shape of copepods (related to the cyclops of their native stream) which abound in the salt water, particularly in early summer. The copepod feeds on diatoms which, in spite of their diminutive size, manage to contain a certain amount of oil. This oil is then transferred to the copepods and thence to the salmon, and that is how the salmon obtains that delicate oil with which its flesh is permeated and, also, that is the reason why a fresh-run salmon is so fat. The herring, too, feeds on similar organisms and consequently it is also oily. Certain other animals such as squids and cuttle fishes feed on the small relations of the shrimp and in turn the cod and halibut feed on them. In the case of these two fishes the oil is appropriated by the liver, hence cod-liver oil and halibut oil -- all derived from the microscopic diatoms. 

The Char.

Incidentally, it is said that potted char makes a delightful breakfast dish. 

The Smelt or Sparling.

One of the most delightful of our fishes, with the delicate blues, greens, yellows and pinks of its coloration, the Smelt is noted principally, perhaps, for the insistent cucumber odour of the flesh. When the smelt-net is being hauled aboard, before it breaks the surface even, the cucumber smell is evident ; if one happens to be out in a boat and many smelt are in the adjacent water, that same piquant scent may be noticed.

The Stone Loach.

Queer little fishes are the loaches with their worm-like bodies and fringe of barbels around their mouths. 

... A strange feature of the loaches generally, though not quite so marked in the British species, is their reaction to thundery weather. The approach of a thunderstorm is sufficient to bring them from the bottom of the pond to dash wildly about near the surface. 

The Common Eel.

During the stay in the estuary certain adjustments are being made to the constitution of the creature's blood ; from an environment that exerts a pressure of fourteen pounds or so to every square inch of the surface of the body it will be moving to one with a pressure of over a ton to every square inch. 

The Pope or Ruffe.

Years ago, more especially in Yorkshire where they held mammoth fishing contests, the habit was to impale a cork upon the spines of the dorsal fins of this fish. The poor fish would then go floating down the stream quite helpless to combat the onslaughts of its many enemies. To the partisans it was great fun, but to the fish it was death. 

The Mullets.

There is a creek that I love well and many a time do I wend my way there early on a morning that promises a hot day. There is a pale blue haze over the water ; the grass of the sea-wall and the distant trees and meadows are bathed in that mist, even the mud of the creek itself reflects many colours, all subdued into pastel tints. A broken down wooden staging -- it was there when the good people of these parts were not averse to a spot of smuggling -- juts out over the mud. Presently the tide will be up and the sea-grass that adorns the ancient woodwork will float out gracefully in the water. Lying on this staging, with one's nose not many inches from the water, the Mullet can be seen clearly. They come up the creek in shoals several hundred strong full of the joy of living. ... 

People, seeing the shoals pass up these narrow creeks, have conceived the bright idea of stretching a net from one side to the other after the fish have passed ; then, when they return to the sea at the turn of the tide, their capture should be an easy matter. In theory it works out very well ; unfortunately, the Mullet is as accomplished an escapist as the late Houdini. The leader of the shoal will search for a weak part of the net, failing that he will attempt to get under the ground rope, and if there is no loophole there he will leap right out of the water over the top of the net. Whichever means of escape proves successful the others will follow, like sheep through a gap in a hedge. This will happen, too, when seine nets are used and the experienced fisherman will spread straw over the water inside the top rope. Consequently the fish will leap too soon and find itself still encircled by the net : just as an eagle will swoop but once, so the Mullet will leap but once. 

gentles : maggots. This angler's term was current until about 1960.