Swimming depth of migrating silver eels Anguilla japonica released at seamounts of the West Mariana Ridge, their estimated spawning sites

Abstract.-The horizontal and vertical movements of 20 silver American eels Anguilla rostrata migrating through a macrotidal estuary and bay were tracked with hydroacoustic telemetry. Eels initiated their seaward migrations around or shortly after sunset, mostly migrated at night, exhibited no bias for migration on ebb versus flood tides, and swam both with and against tidal currents with little preference for depth. Profiles of eel vertical distributions during transit through the estuary, the bay, and the tidal passages that connected the bay to the open sea differed and differed from analogous profiles for silver European eels A. anguilla transiting the Baltic Sea where tidal forcing is negligible. The underlying mechanism(s) associated with their direction of net displacement appears to be innate, although local circulation features may influence transit speeds and exit routes to the open sea. Our results in combination with published information for both the silver American and the European eel suggest that the horizontal migration speed for both species is relatively invariant, around 0.5 body lengths per second. The rate of ascent/descent of eels exhibiting a change in swimming depth of greater than 5 m could not be estimated with precision from the available records of eel swimming depths. The observed average rate of 0.11 m/s was, however, within the relatively narrow range of the average vertical swimming speeds (0.11-0.18 m/s) reported in the literature for silver eels executing vertical dives.

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Morphological alteration in two types of gill chloride cells in Japanese eels (Anguilla japonica) during catadromous migration

Canadian Journal of Zoology ◽

10.1139/z98-072 ◽

1998 ◽

Vol 76 (8) ◽

pp. 1480-1487 ◽

Cited By ~ 29

Author(s):

Seiji Sasai ◽

Toyoji Kaneko ◽

Sanae Hasegawa ◽

Katsumi Tsukamoto

Keyword(s):

Atpase Activity ◽

Anguilla Japonica ◽

Japanese Eel ◽

Morphological Alteration ◽

Immunocytochemical Staining ◽

Chloride Cells ◽

Apparent Difference ◽

Silver Eels ◽

Different Types ◽

Yellow Eels

Gill chloride cell morphology and Na+,K+-ATPase activity were examined in cultured Japanese eels (Anguilla japonica) acclimated to fresh water (FW) or seawater (SW), and in yellow and silver eels caught in wild stocks. Gill Na+,K+-ATPase activity was higher in SW-acclimated cultured eels than in FW eels. Chloride cells were detected in both filament and lamellar epithelia by immunocytochemical staining using anti-Na+,K+-ATPase serum. The filament chloride cells were more abundant and larger in SW eels than in FW eels, whereas there was no apparent difference in lamellar chloride cells. In wild-caught eels, gill Na+,K+-ATPase activity increased as they developed from yellow to silver eels. Filament chloride cells in silver eels were more active than those in yellow eels. In contrast, lamellar chloride cells, which were frequently observed in yellow eels, had decreased in number or disappeared in silver eels. These findings suggest that chloride cells in the filament are responsible for excretion of excess salt in hyperosmotic environments, and that lamellar chloride cells may play a significant role in hypoosmotic environments, presumably acting as sites of ion uptake. The excellent euryhalinity of the Japanese eel may be due, at least in part, to the presence of functionally different types of chloride cells. The activation of filament chloride cells in silver eels in FW, together with the increase in Na+,K+-ATPase activity, could be interpreted as a preadaptive response to forthcoming entry into SW.

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The migration of stocked, trapped and transported, and wild female American silver eels through the Gulf of St. Lawrence

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/cjfas-2017-0356 ◽

2018 ◽

Vol 75 (11) ◽

pp. 2024-2037 ◽

Cited By ~ 1

Author(s):

Mélanie Béguer-Pon ◽

Guy Verreault ◽

David Stanley ◽

Martin Castonguay ◽

Julian J. Dodson

Keyword(s):

Detection Efficiency ◽

Anguilla Rostrata ◽

Migration Speed ◽

Hydroelectric Dams ◽

Wild Female ◽

Swimming Depth ◽

Silver Eels ◽

Diel Vertical Migrations ◽

American Eels ◽

St Lawrence River

The stocking of juvenile eels and trap and transport programs of large yellow (American) eels (Anguilla rostrata) were initiated in Ontario to mitigate mortalities observed at hydroelectric dams and to increase escapement from the upper St. Lawrence River and Lake Ontario (Canada). A total of 380 migrating female silver eels (stocked, trapped and transported, and wild) were tagged with acoustic transmitters between 2011 and 2014. Their migration and escapement at the exit of the Gulf of St. Lawrence, the Cabot Strait, were recorded using acoustic receivers. Escapement rates varied between 8.9% and 20.0% annually (mean = 11.4%). A high proportion of stocked eels were detected (N = 27 of 43 detected at Cabot Strait), demonstrating their ability to escape the Gulf. No differences in migration speed or crossing locations at Cabot Strait were found among the three categories. Eels crossing Cabot Strait did not display diel and tidal patterns, but their estimated swimming depth indicated diel vertical migrations. The low escapement rates observed may be related to predation events and (or) the low and variable detection efficiency of the acoustic receivers’ line.

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