in a day (BENTLEY and FOLLETT, 1963). H ARDISTY (1956) co mpared th e rates of
water uptake in th e river lamprey, after it had undert aken its br eeding mi gration ,
wit h that of brook lampreys (L. planerz) w hich live th eir enti re lives in fresh wa ter.
Aft er making adj ustme nts fo r the differenc es in size of thes e two agnat hans he
fo und th at th e bro ok lamprey accumulated wa ter thro ugh its inte gument at twice
th e rate of the river lamprey . Water moves across th e skin of th e river lamprey at
th e rat e of 2.5 .ullcm2h (in v itro, osmotic grad ient about 210 m-osm ole /l: BENTLEY,
1962 a). This value is sim ilar to that estimated for the entire inte gument (skin and
gills) in v iv o (W IKG REN, 1953). The marine myxin o id agna thans have an integume nt
that is very perm eabl e to water, as seen in th e Pacific hagfish (McFAR LAND and
M UNz, 1965), but as th e osmotic gradient betw een th e body fluid s and th e sea is
small, little water is norm ally accumulated in thi s way, less than 0.5 % of th e bod y
weight in a day in My xin e glutinosa (M ORRIS, 1965).
The relative perm eabilities of the integuments of an osteichthyean and an agnathan fish have been compared with those of the Europ ean fro g (WIKGREN, 1953).
The ratios of th e rates of wate r accumulation across th e inte gument of the eel: river
lamprey: fro g in fresh water are : 1:20 :60.
While their skin is normally not very permeabl e to wa ter, when fish are stresse d,
such as w hen th ey are handl ed , the y excr ete lar ge volumes of urine . This is usu ally
considered to result from damage to th e skin, po ssibl y by remov ing part of th e
coating of mu cou s o n its sur face. Exposure of fish , suc h as th e eel, Anguilla anguilla, and killifish , Fundulus kansae, to externa l so lutio ns th at cont ain no calcium
ma y also produce an inc rease in th e permeability of the skin (SHARRATT et a!', 1964
b ; PICKFORD f~ al., 1966). T hus , despite its somewha t rugged appea rance th e skin
of fishes is a delicate barri er whose int egrity must be co nt inually maintained.
b) The Gut
Fishe s living in fr esh wa te r drink little wate r, but teleosts in the sea mu st sw allow
sea-water in order to co m pe nsate for th eir osmo tic losses (H . SM ITH, 1930 b). Indeed, if marine teleost fish are pr evented from d rinking th ey rapidly die from d ehydration. The rat e of drinking appears to relate dir ectl y to th e fishes' needs, for ,
as th e concentration of the exte rn al media increases, so doe s the amount that th e
fish drinks ; eels in sea-water drink 325 .u1/1OOg h, but if the y are placed in a so lution
twice as concentrated as th e sea, the y drink 800 .u l/ 100 g h (MAETZ and SKA DHAUGE, 1968). The quantity of sea- water swall ow ed by marine teleosts each day
varies from volumes equivalent to 5 % of the bod y weight in the flound er to 12% in
the sea-water perch (T able 7.6). These quantities are pr esumabl y largel y dictated by
the os mo tic water loss of the fishe s, a fact or influenc ed by th eir surface area, as well
as the precise pr op erti es of the skin and gills. There are few determinati o ns of
drinking rat es in non-teleost fishe s ; th e lamprey drinks w hen placed in 50 % seawater and myxinoid s have been o bse rved to drink, but thi s water doe s not appear
to be absorbed (MORRIS, 1965 ; M cFAR LAND and M UNZ, 1965). Marine cho ndr ichthvean s do not ap pear to drink (H . SMITH, 1931).
Ab out 75% of th e sea-wa ter that is imbibed by teleost fishe s is abs orbed int o
the body flu ids. The int est ine abso rbs water, but as thi s is a con sequ ence of th e
211
water uptake in th e river lamprey, after it had undert aken its br eeding mi gration ,
wit h that of brook lampreys (L. planerz) w hich live th eir enti re lives in fresh wa ter.
Aft er making adj ustme nts fo r the differenc es in size of thes e two agnat hans he
fo und th at th e bro ok lamprey accumulated wa ter thro ugh its inte gument at twice
th e rate of the river lamprey . Water moves across th e skin of th e river lamprey at
th e rat e of 2.5 .ullcm2h (in v itro, osmotic grad ient about 210 m-osm ole /l: BENTLEY,
1962 a). This value is sim ilar to that estimated for the entire inte gument (skin and
gills) in v iv o (W IKG REN, 1953). The marine myxin o id agna thans have an integume nt
that is very perm eabl e to water, as seen in th e Pacific hagfish (McFAR LAND and
M UNz, 1965), but as th e osmotic gradient betw een th e body fluid s and th e sea is
small, little water is norm ally accumulated in thi s way, less than 0.5 % of th e bod y
weight in a day in My xin e glutinosa (M ORRIS, 1965).
The relative perm eabilities of the integuments of an osteichthyean and an agnathan fish have been compared with those of the Europ ean fro g (WIKGREN, 1953).
The ratios of th e rates of wate r accumulation across th e inte gument of the eel: river
lamprey: fro g in fresh water are : 1:20 :60.
While their skin is normally not very permeabl e to wa ter, when fish are stresse d,
such as w hen th ey are handl ed , the y excr ete lar ge volumes of urine . This is usu ally
considered to result from damage to th e skin, po ssibl y by remov ing part of th e
coating of mu cou s o n its sur face. Exposure of fish , suc h as th e eel, Anguilla anguilla, and killifish , Fundulus kansae, to externa l so lutio ns th at cont ain no calcium
ma y also produce an inc rease in th e permeability of the skin (SHARRATT et a!', 1964
b ; PICKFORD f~ al., 1966). T hus , despite its somewha t rugged appea rance th e skin
of fishes is a delicate barri er whose int egrity must be co nt inually maintained.
b) The Gut
Fishe s living in fr esh wa te r drink little wate r, but teleosts in the sea mu st sw allow
sea-water in order to co m pe nsate for th eir osmo tic losses (H . SM ITH, 1930 b). Indeed, if marine teleost fish are pr evented from d rinking th ey rapidly die from d ehydration. The rat e of drinking appears to relate dir ectl y to th e fishes' needs, for ,
as th e concentration of the exte rn al media increases, so doe s the amount that th e
fish drinks ; eels in sea-water drink 325 .u1/1OOg h, but if the y are placed in a so lution
twice as concentrated as th e sea, the y drink 800 .u l/ 100 g h (MAETZ and SKA DHAUGE, 1968). The quantity of sea- water swall ow ed by marine teleosts each day
varies from volumes equivalent to 5 % of the bod y weight in the flound er to 12% in
the sea-water perch (T able 7.6). These quantities are pr esumabl y largel y dictated by
the os mo tic water loss of the fishe s, a fact or influenc ed by th eir surface area, as well
as the precise pr op erti es of the skin and gills. There are few determinati o ns of
drinking rat es in non-teleost fishe s ; th e lamprey drinks w hen placed in 50 % seawater and myxinoid s have been o bse rved to drink, but thi s water doe s not appear
to be absorbed (MORRIS, 1965 ; M cFAR LAND and M UNZ, 1965). Marine cho ndr ichthvean s do not ap pear to drink (H . SMITH, 1931).
Ab out 75% of th e sea-wa ter that is imbibed by teleost fishe s is abs orbed int o
the body flu ids. The int est ine abso rbs water, but as thi s is a con sequ ence of th e
211