|
Vol. 53, 2014
Concentrations of osmotically related constituents in plasma
and urine of finless porpoise (Neophocaena
asiaeorientalis):
implications for osmoregulatory strategies for marine mammals living in
freshwater
Aihuan
Guo1,2, Yujiang Hao1*, Jingzhen Wang1,2,
Qingzhong Zhao1 and Ding Wang1*
1Key
Laboratory of Aquatic Biodiversity and Conservation, Institute of
Hydrobiology, Chinese Academy of Sciences, 7th South Donghu Road,
Wuchang District, Wuhan, Hubei 430072, People's Republic of China
2University of Chinese Academy of Sciences, Beijing
100864, China
Abstract
Background: Most cetaceans inhabit
the hyperosmotic marine environment with only a few species living in
freshwater habitats. The Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis) is the only
freshwater subspecies of the genus. Our aim was to study whether the
osmoregulation mechanism of the Yangtze finless porpoise is different
from the marine subspecies, the East Asian finless porpoise (Neophocaena asiaeorientalis sunameri). We assayed and compared
the concentrations of the constituents involved in osmoregulation in
the blood and urine in the Yangtze finless porpoise and the East Asian
finless porpoise. We also compared the corresponding urine constituents
of the porpoises with existing data on fin whales (Balaenoptera physalus) and bottlenose dolphins (Tursiops truncatus).
Results: The mean plasma osmolality of Yangtze
finless porpoise was significantly lower than that of the marine
subspecies (P < 0.01).
Similarly, the urine osmolality of Yangtze finless porpoise was also
significantly lower than that of its marine counterpart (P < 0.05). However, the urine
sodium concentration of freshwater finless porpoise was significantly
lower than that in the marine subspecies (P < 0.01), even though their
serum sodium has no significant difference. Moreover, the freshwater
porpoise has significantly lower urine urea concentration but much
higher serum urea than in the marine finless porpoise (P < 0.05).
Conclusions: These results suggest
that the freshwater finless porpoise does have different osmoregulatory
mechanism from marine cetaceans. Conserving sodium by excreting urine
with low ion levels may be an essential strategy to maintain the serum
electrolyte balance for the freshwater subspecies that also appears to
be more susceptible to hyponatremia.
Key words: Finless porpoise; Osmoregulation;
Plasma; Urine.
*Correspondence: E-mail: hao.yj@ihb.ac.cn; wangd@ihb.ac.cn
|
