Vascular Adaptations for Blood Supply to Locomotory Muscles of Icefish
187
via a Watson-Marlow rotary pump at a rate of 10 ml min-I, passing
through a 0.8 !lm in-line filter. After a clear exudate was observed (5-10
min, depending on the degree of vasodilatation), the perfusate was
changed to 10% neutral formalin while the acrylic casting compound was
being prepared. Batson's No. 17 anatomical corrosion compound is a
suitable casting agent for vascular networks of homeotherms, although it
is quite viscous and particularly unsuitable at low temperatures if
complete filling of the smallest vessels (capillaries) is to be achieved. This
was therefore diluted by a monomeric methyl methacrylate (Sevriton)
which significantly reduced its viscosity. Mixing on ice to retard
polymerization and setting time also improved the extent of filling as
judged by methyl salicylate-cleared material. The final recipe was: 10.0
ml Batson's (A), 3.0 ml Catalyst (B), 0.2 ml Promotor (C), 0.1 ml
Colorant, 6.0 ml Sevriton.
Microscopy
Muscle samples were fixed by immersion in buffered paraformaldehyde/
glutaraldehyde at resting length [8]. Transverse sections of resinembedded material were double stained (lead citrate/uranyl acetate) and
electronmicrographs taken with a JEOL 100 cx II operating at 60 kV.
Casts were mounted on stubs and gold or platinum coated at low power in
a Polaron E5000 sputter coated to a thickness of 10-20 nm before
examination in a Hitachi S-520 Scanning Electron Microscope (SEM) at
lOkV.
Results
In both C. hamatus and C. aceratus a complete set of arterial arches from
the first three gill arches joined to form a vessel which ran posteriorly to a
position ventral to the heart, and then divided into two vessels which
passed laterally and posteriorly to the pectoral muscles, anastomosing
with the subclavian arteries coming from the dorsal aorta (Fig. 1). The
ventral efferents from the 4th gill arches were smaller and divided to
supply local tissues. All icefish species examined showed a similar
pattern, which is illustrated by a drawing of a freshly injected specimen of
C. hamatus (Fig. 2). This functional hypobranchial network [6,9] thus
serves to provide an anastomosing dual arterial blood supply to the main
locomotory (pectoral) muscles. Perfusion resistance will be lowered by
some indeterminate amount, but given the similar diameters of both dorsal
aorta and hypobranchial afferents this is likely to be around a factor of 2.
187
via a Watson-Marlow rotary pump at a rate of 10 ml min-I, passing
through a 0.8 !lm in-line filter. After a clear exudate was observed (5-10
min, depending on the degree of vasodilatation), the perfusate was
changed to 10% neutral formalin while the acrylic casting compound was
being prepared. Batson's No. 17 anatomical corrosion compound is a
suitable casting agent for vascular networks of homeotherms, although it
is quite viscous and particularly unsuitable at low temperatures if
complete filling of the smallest vessels (capillaries) is to be achieved. This
was therefore diluted by a monomeric methyl methacrylate (Sevriton)
which significantly reduced its viscosity. Mixing on ice to retard
polymerization and setting time also improved the extent of filling as
judged by methyl salicylate-cleared material. The final recipe was: 10.0
ml Batson's (A), 3.0 ml Catalyst (B), 0.2 ml Promotor (C), 0.1 ml
Colorant, 6.0 ml Sevriton.
Microscopy
Muscle samples were fixed by immersion in buffered paraformaldehyde/
glutaraldehyde at resting length [8]. Transverse sections of resinembedded material were double stained (lead citrate/uranyl acetate) and
electronmicrographs taken with a JEOL 100 cx II operating at 60 kV.
Casts were mounted on stubs and gold or platinum coated at low power in
a Polaron E5000 sputter coated to a thickness of 10-20 nm before
examination in a Hitachi S-520 Scanning Electron Microscope (SEM) at
lOkV.
Results
In both C. hamatus and C. aceratus a complete set of arterial arches from
the first three gill arches joined to form a vessel which ran posteriorly to a
position ventral to the heart, and then divided into two vessels which
passed laterally and posteriorly to the pectoral muscles, anastomosing
with the subclavian arteries coming from the dorsal aorta (Fig. 1). The
ventral efferents from the 4th gill arches were smaller and divided to
supply local tissues. All icefish species examined showed a similar
pattern, which is illustrated by a drawing of a freshly injected specimen of
C. hamatus (Fig. 2). This functional hypobranchial network [6,9] thus
serves to provide an anastomosing dual arterial blood supply to the main
locomotory (pectoral) muscles. Perfusion resistance will be lowered by
some indeterminate amount, but given the similar diameters of both dorsal
aorta and hypobranchial afferents this is likely to be around a factor of 2.