158 BULLETIN OF THE BUREAU OF FISHERIES. 



material besides the forms mentioned above is shown by the various species of fishes 

 occasionally noted in the food at Monterey. These natural foods are all relatively 

 oily, the point which particularly concerns us here. As digestion proceeds and the 

 protein framework is dissolved away these oils are liberated in the alimentary canal 

 and form no inconsiderable portion of the food of the king salmon. When one remem- 

 bers the characteristics of the salmon flesh, charged with oil as it is, and evidently storing 

 great quantities of oil, the interest which attaches to the question of the source of the 

 oil in the food and the method of digesting and absorbing oils is obvious. 



Asamatterof fact it was in the course of a study of the character and microscopic 

 distribution of the fats in the salmon tissue that I instituted observations on the ali- 

 mentary tract of the king salmon which made it obvious that large quantities of oils 

 were absorbed from the foods in these normal feeding salmon. 



FAT-FED SALMON. 



The inability to control the relation between the time of taking food and the chance 

 of securing the fish and making observ^ations of the stage of absorption in the normal 

 feeding salmon renders it extremely difficult to settle the question of the characteristics 

 of fat absorption in such. As a matter of fact, my observations made it very clear that 

 much absorption of fat was taking place in salmon feeding under natural conditions, yet 

 it was found next to impossible to determine the nature and details of the process from the 

 specimens available. For this reason the idea of feeding salmon in the aquaria was 

 conceived and its immediate execution was made possible through the courtesy of the 

 directors and superintendent of the Brookdale hatchery. Young salmon were transported 

 in live cans from Brookdale to the Hopkins' Seaside Laboratory at Pacific Grove, Cal. 

 Two sizes of salmon were available, one group of yearlings from 6 to 7 centimeters long, 

 and a group of small 2-year-olds from 14 to 16 centimeters long. 



These young salmon were fed olive oil by rectal injection. This was found to be an 

 extremely reliable and easy way of introducing the oil into the alimentary tract in such 

 a way as to give one confidence in the accuracy of the results. A medicine dropper was 

 drawn out in the flame to a slight cone of proper size. A desirable quantity of oil was 

 then taken into the dropper, the tip inserted into the anal aperture and gentle pressure 

 maintained until the oil was emptied into the alimentary tract. It is comparatively 

 easy to hold the young salmon by a firm grip of a lobe of the caudal fin rays, the fish 

 resting in the palm of the hand in such a way that the head and gills remain under water 

 to prevent asphy.xiation. Under these conditions the fish does not struggle as much as 

 might be expected. The slight contractions of the muscles of the anal sphincter occurring 

 when the pipette is first introduced soon relax, but one has always to maintain a gentle 

 pressure on the pipette for a moment before oil begins to flow into the tract. The alimen- 

 tary canal of the salmon is a simple S-shaped tube, as has been described and figured in a 

 previous paper." When the oil is injected into the posterior end of the canal in sufficient 

 quantity it flows into the different limbs of the intestine and into the stomach, and from 

 the stomach will be discharged from the esophagus into the mouth if an excess of oil is 

 used. In my later experiments this fact was adopted as an index of when the proper 

 quantity of oil was administered. 



■I Greene, Charles W.; The anatomy and histology of the alimentary tract of the king salmon, Oncorhynckus tschawytscha. 

 Bulletin. Bureau of Fisheries, vol. .xx.\n, 1912, p. 73-100, pl. xxv-.xxviii. 



