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International Journal of Marine Science 2014, Vol.4, No.44, 1-14
http://ijms.biopublisher.ca
9
A possible explanation for the high hepatic antioxidant
activities in both the ray and skate, as compared with
the dogfish, may be the hypoxic conditions of benthic
environment of the Black Sea. The ray and skate
species included in this study are classified as benthic
dwelling species. In general, benthic biotops are
characterized by oxygen deficient conditions when
compared with the top water layers. Several
researchers have noted that in hypoxic conditions
antioxidant defense is significantly enhanced in fish
(Hermes-Lima et al., 2001; Welker et al., 2013). This
is an evolutionary adaptation, that may play an
important role when species venture into habitats with
low concentrations of oxygen, such as when foraging
or dwelling on the bottom. This adaptation allows fish
to cope with oxidative stress arising from tissue
reoxygenation (Lushchak and Bagnyukova, 2006).
More research regarding the antioxidant system of
elasmobranchs, especially in deep habitats
characterized by hypoxic and/or anoxic conditions are
needed to understand the development of antioxidant
defenses in aquatic animals. This is extremely
important for the Black Sea ecosystem as it is one of
the largest anoxic seas in the world. Furthermore, its
deep waters contain high concentrations of hydrogen
sulphide (Fashchuk and Sapozhnikov, 1999) or,
perhaps, other unknown toxins that triggers
antioxidant defenses. Benthic fish, including the
elasmobranchs in this study migrate or dwell entirely
in anoxic/hypoxic zones in the sea, and high level of
antioxidants in their tissues may be a physiological
adaptation to prevent oxidative stress (Welker et al.,
2013).
Despite
these
correlations,
further
investigations of the biochemical strategies for dealing
with oxidative stress in fish inhabiting deep waters,
and those containing hydrogen sulphides are needed.
Another explanation for the increased antioxidant
enzyme activities in the liver of skates as compared
with dogfish may be explained by the high
concentration of low molecular weight scavengers
(vitamins E, A, K, carotenoids, and glutathione) in
shark tissues combined with the high concentrations
of lipid peroxidation substances (Filho and Boveris,
1993; Filho et al., 1993). These low molecular weight
scavengers may have evolved to serve as an
antioxidant defense in sharks (Martinez-Alvarez et al.,
2005). Therefore, the shark, unlike the skate, may not
require the same elevated levels of antioxidants in the
liver since the low molecular weight molecules serve
the same evolutionary role.
An increase of aminotransferase enzyme activity in
the blood serum, plasma and other extracellular fluids
was shown in the tissues of the organisms impacted
unfavorable conditions, organ dysfunction or internal
lesions in tissues. The damaged cells release their
contents (including aminotransferases) towards the
blood stream, and the level of these enzymes enhances
in serum (Martinez-Porchas et al., 2011). AST is used
as clinic diagnostic tool, and it is associated with cell
necrosis of the liver and skeletal or cardiac muscle,
starvation and lacking of vitamin E. Plasma ALT is an
acute hepatic damage good marker (Coppo et al.,
2001~2002).
Our findings also demonstrate interspecies differences
of aminotransferases (ALT and AST) activity in fish
liver: in dogfish the enzyme (both ALT and AST)
activity was the highest, in stringray and in buckler
skate it was lower. We propose that these interspecies
differences depend on fish ecological status; rays and
skates are generally benthic or epibenthic slow
swimming forms, and dogfish is an active pelagic
animal. An increase of aminotransferase activity in the
dogfish may be explained by the high metabolic rate
and swimming activity of this species, while ray and
skate have lower metabolic rates.
The de Rytis coefficient was higher in the skate and
ray compared with shark which could be associated
with lack of oxygen in bottom biotops. This agrees
with the observations of several researchers who
showed that enzyme activity ranges in fish widely, and
depends on species biological specificity and
swimming activity (Goto et al., 2003; Treberg et al.,
2003), age (Coppo et al., 2001-2002), sex, maturation
stage (Mehdi et al., 2011), period of reproduction
(Svoboda et al., 2001) and animals adaptation to
different salinities (Ip et al., 2009). Thus, the de Rytis
coefficient (AST/ALT) differences in sharks vs
rays/skates reflect the specificity of habitats of
examined fish, particularly the oxygen concentration
in waters because the lack of oxygen in the
environment and in tissues led their damage and
enzyme activity changes.
Aminotransferases activity in blood serum of buckler
skate was the highest as compared with the values of