Lim Jeanette, Fudge Douglas S, Levy Nimrod, Gosline John M
Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, BC, V6T 1Z4, Canada.
J Exp Biol. 2006 Feb;209(Pt 4):702-10. doi: 10.1242/jeb.02067.
Hagfish are able to produce substantial amounts of slime when harassed, but the precise ecological function of the slime is unclear. One possibility is that the slime acts as a defence against gill-breathing predators, whose gills may become entangled with the slime's mixture of mucins and fibrous threads during an attack. We previously demonstrated that hagfish slime does not bind water tightly, but instead behaves like a fine sieve that slows water down via viscous entrainment. These properties are consistent with the gill-clogging hypothesis, which we tested here by quantifying the effects of hagfish slime on water flow through an artificial gill model and real fish gills. Our results indicate that the slime is capable of clogging gills and increasing the resistance that they present to the flow of water. We also characterized the behaviour of slime release from live hagfish and the effect of convective mixing on the formation of slime in vitro. Our observations show that exudate is locally released from the slime glands as a coherent jet and that hagfish do not appear to use their slime as a protective envelope. We found that convective mixing between the exudate and seawater is necessary for proper slime formation, but excessive mixing leads to the slime's collapse. We suggest that the loose binding of water by the slime may be an optimal solution to the problem of delivering an expanding jet of flow-inhibiting material to the gills of would-be predators.
盲鳗在受到骚扰时能够分泌大量黏液，但这种黏液的确切生态功能尚不清楚。一种可能性是，这种黏液起到抵御鳃呼吸捕食者的作用，在攻击过程中，捕食者的鳃可能会被黏液中的黏蛋白和纤维丝混合物缠住。我们之前证明，盲鳗黏液与水的结合并不紧密，相反，它的行为就像一个细筛，通过黏性夹带减缓水流速度。这些特性与鳃堵塞假说相符，我们在此通过量化盲鳗黏液对通过人工鳃模型和真实鱼鳃的水流的影响来验证这一假说。我们的结果表明，黏液能够堵塞鳃并增加鳃对水流的阻力。我们还描述了活盲鳗释放黏液的行为以及对流混合对体外黏液形成的影响。我们的观察结果表明，分泌物作为一股连贯的射流从黏液腺局部释放，而且盲鳗似乎并不将其黏液用作保护包膜。我们发现，分泌物与海水之间的对流混合对于黏液的正常形成是必要的，但过度混合会导致黏液坍塌。我们认为，黏液对水的松散结合可能是将一股不断扩展的抑制水流物质射流输送到潜在捕食者鳃部这一问题的最佳解决方案。
