The effects of salinity on the growth and mortality rates and osmotic pressure and its application to adaption and habitat use of giant mottled eel Anguilla marmorata
Date Issued
2010
Date
2010
Author(s)
Lin, Yang-Han
Abstract
The giant mottled eel, Anguilla marmorata, was listed as an endangered species in Taiwan where its culture and capture was banned in the past 20 years, but just recently,the government lifted the ban in April 2009. Due to its high economic and commercial value, the giant mottled eel has been a good candidate for aquaculture. However, the biological information for culture practices and resources management is still unknown. In addition to this, the interspecific competition for habitat-use in the wild with its congeneric species A. japonica was also unclear. Meanwhile, it was believed that A marmorata inhabited high saline environment in some of the Japanese waters, which was contradictory to the general knowledge. To clarify the salinity preference, and the optimum conditions for A marmorata. Also it aims to understand the effect of salinity on mortality and growth rates of the eel. The following 4 experimental designs were formulated to understand the effect of salinity on the growth and survival rates of A. marmorata 1) compare of the growth and survival rates of A. japonica and A. marmorata elvers in both artificial and natural sea water under different salinities. 2) compare the growth and survival rate of VB stage A. marmorata glass eels in different salinities 3) compare the osmolaritic pressure and NKA activities of the elvers in different salinity in short (48hrs) and long term (2 months) acclimatization and 4) establish the relationship between different salinities and the otolith Sr/Ca ratio to understand the habitat-use of the giant mottled eel in the wild.
The results indicated that in artificial seawater the mean (±SD)mortality rates of A. japonica and A. marmorata dramatically increased from 0% in 0‰ salinity to 34±10% and 94±2% in 10‰ and 66±2%、100% in 15‰, respectively. In natural sea water, the mean(±SD) survival rates in both species were not significant(84~97％ V.S 80~97％). Both species showed better growth in fresh water than saline water. A. marmorata glass eels stage also grew better in fresh water than saline water. In addition, the survival rate of A. marmorata in the first month was not different among experimented groups, but dramatically increased in the second month along with the processing pigmentation stages. These indicated that the survival rates was better in fresh water than in sea water. The osmolarity pressure was higher in sea water than fresh water, but no difference was observed among different salinities. The NKA activity of the eel was approx 3.42 folds higher in sea water than fresh water. The otolith Sr/Ca ratio can distinguish the eel living in freshwater and saltwater environment. In conclusion, the giant mottled eel has salinity adaptation abilities and both A. japonica and A. marmorata prefer fresh water than sea water. These two species may have interspecific competition in Taiwan rivers.
Subjects
Anguilla marmorata
Growth and mortality
Otolith
Salinity adaptation
Osmotic pressure
SDGs
Type
thesis
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