284 UTILITARIAN ZOOLOGY 



poda can be regarded as approximately 975 billion, or for the 

 16 square miles of the Eckenforde fishery district [in the West 

 Baltic] a grand total of 15,600 billion. A billion Copepoda yield 

 not less than 1500 kilograms of dry organic substance, so that the 

 15,600 billion weigh not less than 23,400,000 kilograms [ie. more 

 than 22,982 tons]. Taking the average weight of an adult West 

 Baltic herring as being 60 grams, and allowing that every herring 

 uses in fifty days its own weight of organic substance, we find that 

 every herring consumes annually 438 grams. In the 16 square 

 miles of the Eckenforde fishery district there exists food in the 

 shape of Copepoda for 534,000,000 herring of an average body 

 weight of 60 grams. This result may, of course, be largely 

 problematical, but it is at any rate extremely interesting. The 

 North Sea, in a similar manner to the Baltic, contains an 

 abundant wealth of Copepoda. The open ocean, on the other 

 hand, contains much less." The number of floating fish-eggs of a 

 particular kind contained in plankton may be used as a basis for 

 determining the number of fish of the sort present in a given area 

 at a given time. Applying this method to the cod and plaice of 

 the Eckenforde, Hensen estimates that "man captures for his own 

 use every year about one-fourth of the total number of adult fish 

 in this particular area of the West Baltic. This result is surprising 

 to those who consider the resources of the sea as inexhaustible, 

 and believe that the number of fish caught by man bears only a 

 small proportion to the number actually present in the sea." It 

 is also interesting to learn that the northern seas are richer in 

 plankton than those in warmer latitudes. The possibilities of the 

 Hensen methods are thus seen to be very considerable, but it is 

 unsafe to generalize from a small number of determinations, for 

 the distribution of plankton in a given area is by no means uni- 

 form. In this, and many other matters involving accurate scien- 

 tific research, large government subsidies are urgently needed in 

 this country. We are co-operating, it is true, with other nations 

 in a scientific survey of the North Sea for the space of three years, 

 but during that period the annual grant of ^2000 per annum to the 

 Scottish Fishery Board is suspended, thus seriously crippling an 

 organization that has long been engaged in work of the most 

 valuable kind. 



Fish-Culture (Pisciculture). — The rearing of fishes in ponds 

 is a very ancient art, which was practised by the Egyptians, 



