Water ^q 



li are absent in adults, although there may be pscudoglomeruli in the voung. 

 In the toadfish ^^ the urine flow is only 2.5 ml., kg./dav as compared with 

 300 ml./kg./day in fresh-water catfish. Apparently the glomeruli degenerate 

 with age and become nonfunctional. The t\picai marine teleostean kidney 

 lacks the distal convoluted segment in the tubules. It is as if the glomerulus, 

 an adaptation for filtration of water, and the distal convoluted tubule, which 

 reabsorbs salt in fresh-water forms, have been lost with disuse. Grafllin'*'^ 

 described a Siamese pipefish (Microphis hoaja) which has reinvaded fresh 

 water and lacks both glomerulus and distal convoluted segment; hence glom- 

 eruli are not a sine qua non for life in fresh w^ater. 



Excretion by an aglomerular kidney is essentially tubular secretion. Phenol 

 red and numerous acid dyes are concentrated by the aglomerular toadfish 

 kidney. ^^^ A normal sculpin can excrete such a supersaturated Mgl 1P04 

 that the urine is turbid. -°- 



That the gills are the route of extrarenal excretion was clearly shown in the 

 eel by perfusion of a heart-gill preparation. '■'" Chloride is secreted outward 

 into sea water containing nearly three times as much CI as the blood. When 

 the perfusion fluid in the blood vessels was increased in osmotic concentration, 

 the chloride transported outward was increased. When eels are in fresh water 

 the blood freezes at about —0.11° and at this internal concentration Kevs 

 found Httle or no outward secretion of Cl~. Thus the active chloride transport 

 by the gills is an adaptation to marine and brackish-water life. It is calculated 

 that the gill activity costs 0.1-0.3 cal./gm. of gill tissue/hr.-" Schlieper-'"* 

 confirmed Keys' experiments and showed that water and CI" are transported 

 independently by the gills. Secretion of NaCl could be stimulated by XaCl, 

 Na2S04, glucose, or saccharose. In the epithelium of the gills of Fundulus 

 are secretory cells which appear to eliminate chloride when the fish is in sea 

 water and to take in chloride when the fish is in fresh water. ''•' When the 

 fish are in sea water or when fresh-water fish are injected with sodium chloride, 

 these cells contain a distal vesicle which gives a histochemical test for chloride. 



Marine teleosts, therefore, maintain blood concentratio"ns similar to those of 

 fresh-water teleosts; their kidneys still excrete urine hypotonic to the blood. 

 The kidneys are, then, a liability, and the distal convoluted tubule and, in 

 some fish, the glomeruli are lost. To rid themselves of excess salt the fish drink 

 much sea water and excrete by way of the gills (and possibly oral membranes^ 

 considerable salt and nitrogenous wastes. It may be that Amphibia have not 

 successfully invaded the ocean because of the lack of a mechanism of extra- 

 renal salt elimination. 



Anadromous and Catadromous Fish. Many fish can live in either fresh or 

 salt water. In general, their curves relating internal to external concentration 

 are relatively flat. The blood of salmon in Monterey Bay freezes at —0.762°, 

 blood of the salmon from the head of the tidal water on the Sacramento River 

 freezes at —0.737°, while blood from fish at their fresh-water spawning 

 grounds freezes at —0.668°. ^^ Thus the king salmon blood is diluted by 

 about 12 per cent on going to its breeding territory. Comparable values were 

 found for Atlantic salmon in brackish and fresh water. •'^- 



The killifish, Fmidiihis hetewclmis, lives well in either fresh or sea water. 

 When it is transferred from one medium to the other there is a transitory 

 initial gain (F.W.) or loss (S.W.) of weight. Acclimatization as based on body 



