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<p>The low specific gravity (SG) of ambient water may limit the establishment of freshwater resident populations in marine-originated diadromous fishes. To test this unexamined hypothesis, the SG modulation ability of newly hatched larvae was compared among three diadromous goby species in <i>Gymnogobius</i>, only one of which has freshwater resident populations in addition to the diadromous ones. We first measured the body SG of larvae reared in freshwater and seawater using solutions with SG values ranging from 1.0010 to 1.0490. Then, their swimming layer was observed under laboratory freshwater and seawater conditions. Results showed that regardless of whether the species has freshwater residents or not, the larval SGs were nearly equal to those of the rearing water, i.e., freshwater (~ 1.00) or seawater (~ 1.03). Consistently, the swimbladder of freshwater-reared larvae was significantly more inflated than that of seawater-reared individuals. Furthermore, rearing salinity did not greatly alter their swimming layer in any species. Thus, contrary to expectations, the ability of early larvae to maintain neutral buoyancy in freshwater may not limit the establishment of freshwater residents. The high ability to modulate body SG may contribute to the regulation of larval dispersion during the planktonic period through the flexible selection of swimming layers.</p>

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Larval body buoyancy in diadromous gobies and its potential role in the colonization of freshwater environments

  • 期刊论文

  • 发表日期：

    2025年7月20日

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  • Yumeki Oto,
  • Katsutoshi Watanabe

摘要

The low specific gravity (SG) of ambient water may limit the establishment of freshwater resident populations in marine-originated diadromous fishes. To test this unexamined hypothesis, the SG modulation ability of newly hatched larvae was compared among three diadromous goby species in Gymnogobius, only one of which has freshwater resident populations in addition to the diadromous ones. We first measured the body SG of larvae reared in freshwater and seawater using solutions with SG values ranging from 1.0010 to 1.0490. Then, their swimming layer was observed under laboratory freshwater and seawater conditions. Results showed that regardless of whether the species has freshwater residents or not, the larval SGs were nearly equal to those of the rearing water, i.e., freshwater (~ 1.00) or seawater (~ 1.03). Consistently, the swimbladder of freshwater-reared larvae was significantly more inflated than that of seawater-reared individuals. Furthermore, rearing salinity did not greatly alter their swimming layer in any species. Thus, contrary to expectations, the ability of early larvae to maintain neutral buoyancy in freshwater may not limit the establishment of freshwater residents. The high ability to modulate body SG may contribute to the regulation of larval dispersion during the planktonic period through the flexible selection of swimming layers.