Observations of gut contents of anguilliform leptocephali collected in the western North Pacific

Abstract

The gut contents of anguilliform leptocephali collected by research cruises in the western North Paciˆc were examined in order to investigate their food sources. Gut contents of 26 leptocephali (Anguillidae, Congridae and Serrivomeridae) examined were amorphous food material containing many small spherical particles. Alcian Blue (AB)-stained aggregates containing spherical particles approximately 2 10 mm in diameter were observed in 14 leptocephali from the 2015 survey, and Coomassie Brilliant Blue (CBB)-stained aggregates containing spherical particles about 2 mm in diameter were observed in 12 leptocephali from the 2016 survey. Red auto‰uorescence of phytoplankton was exhibited in several sized cells in amorphous food material. Furthermore, polysaccharide-containing transparent exopolymer particles (TEP), proteinaceous Coomassie stainable particles (CSP), and pico/ nano-planktonic particles about 2 mm in diameter were observed in environmental water samples. These results suggest that anguilliform leptocephali utilize phytoplankton-derived particulate organic matter (POM) as one of the food sources. Such feeding ecology makes it possible for anguilliform leptocephali to avoid food competition from predatory, zooplanktivorous and omnivorousˆshes that have higher trophic positions in the oligotrophic ocean. キーワードウナギ，凝集物，消化管内容物，餌料，多糖類，タンパク質，ピコナノプランクトン，レプトセ ファルス

Onboard rearing attempts for the Japanese eel leptocephali using POM-enriched water collected in the Western North Pacific

“…This assumption is consistent with the low trophic position of the eel leptocephali (Otake et al, 1993;Kimura and Tsukamoto, 2006;Chow et al, 2010;Miyazaki et al, 2011;Miller et al, 2013) and the feeding apparatus constrained to feed on small and/or soft particle (Bouilliart et al, 2015). Since the nets (CMS and MS) used in the present study were 60 and 30 mm in mesh size, the aggregates and small spherical POMs reported by Tomoda et al (2017) were not adequately collected and supplied to the leptocephali during the experiments in this study. Development of a method to collect large amount of seawater together with such fine particles and soft aggregates is necessary to elucidate the efficacy of the small POMs as the feed for the Japanese eel leptocephali.…”

“…Recently, Tomoda et al (2017) found that Alcian-blue stained aggregates (polysaccharides), Coomassie-brilliantblue stained aggregates (proteins) and small spherical particle (2-10 mm in diameter) were common between the environmental water and the gut contents of anguilliform leptocephali, suggesting POM originated from phytoplankton and cyanobacteria to be food sources for the leptocephali. This assumption is consistent with the low trophic position of the eel leptocephali (Otake et al, 1993;Kimura and Tsukamoto, 2006;Chow et al, 2010;Miyazaki et al, 2011;Miller et al, 2013) and the feeding apparatus constrained to feed on small and/or soft particle (Bouilliart et al, 2015).…”

“…1). Large zoo-and phytoplanktons observed in POMEW350 during 2013 cruise did not exist in POMEW25 and POMEW53, while small amount of amorphous materials and small spherical particles (∼20 mm) were observed (see Tomoda et al, 2017). Neither melanized gut nor necrosis in the leptocephali was observed, but unidentified whitening disease caused low survival for all rearing lots.…”

“…diameter mouth opening, 2 m long, 60 mm mesh) (Itoh and Mochioka, 2005) with a 200 mL cod end bottle was used in 2013 and supplementarily in 2015. MS (marine snow) net (1.14 m diameter mouth opening, 2.6 m long, 30 mm mesh) (Tomoda et al, 2017) with a 5 L cod end bottle was used in 2014 and 2015. The location and depth of POM sampling were varied, since the main purpose of the research cruise was plankton survey and the weather conditions affected the handling of net especially for the MS.…”

“…Amorphous materials appear to be the major gut contents in wild leptocephali, while fecal pellets of zooplankton, larvacean houses, appendicularians, and aloricate protozoa have been also observed in much smaller amounts in many anguillid leptocephali (Otake et al, 1993;Mochioka and Iwamizu, 1996;Govoni, 2010;Miller et al, 2011;Tomoda et al, 2017). Thus, accumulating information on the gut content and low trophic position of the eel leptocephali (Otake et al, 1993;Mochioka and Iwamizu, 1996;Kimura and Tsukamoto, 2006;Chow et al, 2010;Miller et al, 2011Miller et al, , 2013Miyazaki et al, 2011;Tomoda et al, 2017) suggest that particulate organic matter (POM) including marine snow may be the natural diet for eel leptocephali.…”