6 U. S. BURKAU OF FISHERIES. 



To prevent this oxidation it may be sufficient to coat the nets with 

 a covering like tar or linseed oil; it is, however, probable that tan- 

 ning the fibers makes the fibers less likely to heat. The simple pre- 

 caution of washing the nets clean and drying them while spread out 

 is usually sufficient to prevent damage from overheating. 



It is further possible that the products formed by the decomposi- 

 tion of fish slime and oil are injurious to nets. 



Scarcely any treatment will confine itself to preventing any one 

 of the attacks on nets mentioned above, but should be directed toward 

 prevention of all causes of disintegration. The successful process 

 must («) destroy bacteria or prevent their action, (h) make the 

 threads insoluble and proof against the digestive action of bacteria, 

 and (c) prevent oxidation by coating the fibers or making them 

 proof against oxidation. 



COLORING OF NETS. 



Before consideration is given to net-preserving materials, another 

 purpose of curing nets should be mentioned. When nets are treated 

 or cured, their color is usually changed, and it is argued that a less 

 conspicuous net is less likely to frighten away fish. This is a dis- 

 puted point (see Jessen, 1910),® though it might seem perfectly 

 natural that an invisible or poorly visible net would be less likely to 

 frighten fish. It must be remembered, however, that a fish does not 

 see through human eyes but through fish eyes and that a color that 

 is conspicuous to our eyes might not be readily discerned by a fish. 

 The French sardine fishermen use (at least they did several years ago) 

 a combination of soap and bluestone that imparted a bright green 

 color to the nets ; it was claimed that these caught more fish than nets 

 not dyed. The Norwegians have a word, " /?.S'/'e//r/," that they apply 

 to nets that are good catchers of fish. Bluestone is applied to nets 

 (by methods to be mentioned later) to make them fiskelig by mak- 

 ing them bluish green. This is done, of course, on the assumption 

 that if the net is in color similar to sea water the fish can not see it 

 Avell and so do not avoid it. 



Many scientific investigations have been conducted to determine 

 whether fishes can distinguish colors or not. Most of the evidence 

 goes to shoAv that they can; but perhaps they can see fewer colors 

 than humans can. Some investigators have secured evidence that 

 fishes do not distinguish color but that they get different amounts 

 of light from different colors. Thus, a bright green would give more 

 light, or appear lighter in shade, than a dark red, though a fish could 

 get no effect of greenness or of redness. It is also possible, even 

 probable, that different kinds of fish have different abilities to see 

 colors. Thus, it is argued, light does not penetrate very deep into 

 water, and so fishes living at some depth could not see colored ob- 

 jects, even if they had eyes equipped for color vision; and, since 

 nature does not commonly provide useless organs or powers, coloi- 

 vision is not among the accomplishments of bottom-living fishes. 



" Author's name, with year rapntioned in paronthesis. refers to the " Citation of Liter- 

 ature " at the end of this paper. For (^xami)ic : .lessen (I'.tlO) reftn-s to the paper by 

 Peter Jessen,, published in 1910, a. reference to which will be found at the end of this 

 paper. 



