Because, generally, fish do not then feed in the middle of the day, unless the weather be very dark and gloomy - during drizzling rain - or a light breeze of wind.
Because they are active during the night, and in the day remain in a state of repose. Hence the inhabitants of islands and coasts, who live on fish, choose the night for catching them. - Blumenbach.
Because they are capable of living either in fresh or salt water at pleasure. Such fish, in an economical point of view, are extremely valuable, as they furnish to the inhabitants of this and other countries, an immense supply of food. The salmon is an instance in Scotland, where from one river, (Tay) 50,000 head of full-sized fish have been procured in one season. To the Greenlanders, their salmon is, perhaps, more valuable ; as it is dried hard, then broken and pounded, and formed into bread, - as well as consumed in a fresh or salted state.
Because the element in which they reside, preserves them from the pernicious influence of sudden changes of temperature : the process of ossification, (or growth of bones) is very slow in them; their blood is very cold - and their primary movements tardy. Accordingly, we find the age of the carp has been known to reach 200 years, and the pike to 260. " The marks, however, by which the age of fishes may be determined, remained to be discovered." - Fleming.
Because, during every period of its existence, it is surrounded by foes; and when no longer able to exercise its wonted watchfulness, or exert its power of defence, it falls an easy prey to its more powerful adversaries.
Because they appear to prefer certain altitudes. Thus, in ascending mountains, we may observe, that the fish in the lakes and rivers have their boundaries, as well as the vegetables which cover their surface. Wahlenberg found that the pike and perch disappeared from the rivers of the Lapland Alps, along with spruce fir, and when 3,200 feet below the line of perpetual snow. Ascending 200 feet higher, the gwiniad and the grayling, were no longer to be found in the lakes. Higher up still, or about 2,000 feet below the line of perpetual snow, the char had disappeared; and beyond this boundary, all fishing ceased.
Because, in general, the oil is obtained from the livers of the fish, in which it is lodged in cells; but, as it cannot be procured completely from livers by mere boiling, they are allowed to become a little putrid, that the oil may be more readily extracted, by the rupturing of the cells. Along with the oil various other impurities are obtained, as bile, gelatinous matter, etc.