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Fishery Bulletin 111(3) 
site walls of lamellae are connected to each other half- 
way in the hemolymph space. As common gill epithelial 
cells, pillar cells perform respiratory or salt transport- 
ing function depending on their localization within the 
gills and also are thought to play a role in stabilizing 
the lamellae against ambient and internal hydrostatic 
pressure (Compere et al., 1989; Johnson, 1980). Large 
fluctuations of ambient pressure can cause damage of 
the lamellae because the fragile pillar cells are not well 
adapted to withstand pressure forces. In our experi- 
ments, we observed disruption in the connections of pil- 
lar cells and collapse of the lamellae in gills of snow 
crab and southern Tanner crab that were subjected to 
repeated pot hauls (Fig 9). 
The phyllobranchiate gills of brachyuran crabs are 
supplied with low pressure venous hemolymph. The af- 
ferent to efferent drop in pressure and mean internal 
pressure are generally only a few centimeters of water 
(Blatchford, 1971). During normal forward ventilation 
of gills by the scaphognathites, the lamellae tend to be 
inflated by a small positive transmural pressure, which 
is the difference between the above-ambient pressure in 
the lamellar hemocoel and subambient mean pressure 
in the branchial chamber in crab. Under these condi- 
tions, the resistance to hemolymph flow through the cir- 
culatory channels in the gills of crabs is low (McMahon 
and Burnett, 1990). However, any damage to gill struc- 
ture could lead to a significant increase in gill resistance 
and consequently to increases in both the drop in pres- 
sure through the gills and in mean internal pressure 
(Taylor, 1990). Increased pressure in the injured gills 
likely would cause further gill damage and even greater 
impairment of gill function. 
The main factor that determines the internal pres- 
sure in the gills of crabs is thought to be the total vol- 
ume of internal fluid. One of the mechanisms for ad- 
justment of a total fluid volume is regulation of urine 
release (Taylor, 1990). He is the major extracellular 
protein of crab hemolymph; hence, it is [He] that deter- 
mines colloid osmotic pressure of blood plasma. In inter- 
molt marine crabs, the small excess of hydrostatic pres- 
sure of hemolymph over colloid osmotic pressure drives 
passive filtration, which forms primary urine (Mangum 
and Johansen, 1975). The decrease in [He] may elevate 
the driving force for urine formation and, consequently, 
may lead to a decrease in total volume of internal fluid 
in crabs. In our experiments, blood sampling from crabs 
became more difficult after repeated pot hauls because 
the exhaust velocity of hemolymph from the cut was re- 
duced. At the same time, the clotting time of hemolymph 
in experimental crabs was not changed or was increased 
compared with the clotting time in control animals (data 
not shown). These data indirectly indicate a decrease in 
blood pressure in the leg sinus that may be caused by a 
decrease in total volume of hemolymph. 
A decrease in total blood volume through a decrease 
in [He] could not only prevent further gill damage but 
also reduce cardiovascular workload. However, a de- 
crease in [He] causes a decline in the 02-carrying capac- 
ity of hemolymph that, in combination with impaired gas 
exchange in the damaged gills, could lead to a further 
decrease in supply of O 2 to organs and tissues. Studies 
of the role of crustacean He in O 2 transport have found 
complete oxygenation of He in postbranchial hemolymph 
but only partial deoxygenation of He in the tissues of 
normoxic, routinely active animals. The oxygenation 
level of He in the prebranchial hemolymph of resting 
normoxic animals (often called venous reserve) usually 
amounts to 50% or more of the O 2 capacity of the hemo- 
lymph. Reduced O 2 supply to the blood transport system 
or increased metabolic demand could result in depletion 
of the venous reserve. In normoxic conditions, the con- 
tribution of He to O 2 transport significantly increases 
during physical exercises (e.g., locomotor activity) of ani- 
mals (Truchot, 1992; and references therein). 
In our previous studies of [He] in the hemolymph of 
red king crab ( Paralithodes camtschaticus ) in the Bar- 
ents Sea and in the Sea of Okhtosk, [He] during the 
molt cycle was closely correlated with the volume of the 
limbs filled with muscular tissue (Moiseeva and Moi- 
seev, 2008; Moiseeva and Moiseev, 2011). Those results 
also indicate that the O 2 delivery system with He is 
required primarily to support high levels of locomotor 
activity of crabs. Therefore, reduction of [He] and a si- 
multaneous decrease in locomotor activity of crabs could 
optimize blood flow in gills damaged by fisheries opera- 
tions without a significant decrease in supply of O 2 to 
organs and tissues. 
Decompression, which results from a rapid lift of a 
pot to the surface of the water, is not a natural envi- 
ronmental stressor for crabs. However, our experiments 
showed that crabs quite successfully adapted to the 
damage of organs and tissues caused by decompres- 
sion because they took advantage of existing physi- 
ological mechanisms. The gills of crabs are damaged 
often under natural conditions. In our experiments, in 
September-October 2010 in the northern Sea of Okh- 
tosk, gross examination of tissues and organs revealed 
areas of melanization and necrosis in the gills of 40% 
of 50 freshly caught snow crab that had no sign of shell 
disease. In some crab, parts of some of the gills were 
absent (data not shown). Histological examination of or- 
gans and tissues has revealed histopathological changes 
in gills in 95% of snow crab with signs of shell disease 
(Ryazanova, 2006). 
Gills serve an important role in the immune response 
of crustaceans. Aggregates of hemocytes and bacteria ap- 
pear in hemolymph in response to microbial pathogens 
and then become trapped in the narrow hemolymph 
spaces of gills, where they are melanized and persist for 
a long time. The formation of hemocyte aggregates in 
blue crab that were injected with bacteria led to increas- 
es in vascular resistance across the gills and subsequent 
significant increases in the drop of hydrostatic pressure 
across the gill circulation (Burnett et al., 2006). There- 
fore, impairment of respiratory circulation apparently 
occurs often during infectious and noninfectious gill 
disorders of crabs. Crabs would be expected to possess 
