Nutrition & Physiology

Although P. notatus is a very small organism, with young adults ranging from 15-23 cm, it has a very interesting physiology. It is bioluminescent, and has many photophores on its head and running down most of its body (Tsuji et al., 1972). The photophores are the structure which allows P. notatus to illuminate. As mentioned previously, they are activated during courtship, and as a means of camouflage (Harper and Case, 1999). Interestingly enough, despite producing identical photophores, individuals found in the Puget Sound are unable to illuminate (Tsuji et al., 1972). Illumination can normally be induced by injecting an individual with epinephrine, norepinephrine, or amphetamine, but individuals from the Puget Sound are unable to even be made to illuminate (Tsuji et al., 1972).

P. notatus needs a special chemical in order to illuminate, called luciferin. It is not able to reuse old luciferin, meaning it needs to take in the chemical through its diet (Mensinger and Case, 1999). Individuals that were made to illuminate were eventually unable to illuminate until fed a luciferin-containing diet. Wild Midshipman Fish usually intake luciferin by eating ostracod crustaceans (Tsuji et al., 1972).

 Western Gull with Plain Fin Midshipman Fish.


It is a consumer of ostracods (a similar species can be found here), but it is not at the top of the food chain. It is preyed upon by many species! (Eschmeyer et al., 1983), with one notable example being the bald eagle (Elliot et al. 2003). (You can learn  more about other organisms in its food web by clicking: heron and sea otter.)  Bald eagles are known to congregate in areas where a guaranteed meal will be. A large population of Plainfin Midshipman fish lives at Crescent Beach, British Columbia. Bald eagles will take advantage of the free source of food provided by P. notatus (Elliott et al., 2003).

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