Research Article: Nitrogenous compounds characterized in the deterrent skin extract of migratory adult sea lamprey from the Great Lakes region

Date Published: May 23, 2019

Publisher: Public Library of Science

Author(s): Amila A. Dissanayake, C. Michael Wagner, Muraleedharan G. Nair, Daniel Rittschof.

http://doi.org/10.1371/journal.pone.0217417

Abstract

The sea lamprey (Petromzons marinus) is a devastating invasive species that represents a significant impediment to restoration of the Laurentian Great Lakes. There is substantial interest in developing environmentally benign control strategies for sea lamprey, and many other aquatic invasive species, that employ the manipulation of semiochemical information (pheromones and chemical cues) to guide the movements of invaders into control opportunities (e.g. traps, locations for safe pesticide application, etc.). A necessary precursor to the use of semiochemicals in conservation activities is the identification of the chemical constituents that compose the odors. Here, we characterize the major nitrogenous substances from the water-soluble fraction of a skin extract that contains the sea lamprey alarm cue, a powerful repellent that has proven effective in guiding the movements of migrating sea lamprey in rivers. Nitrogenous compounds are suspected components of fish alarm cues as the olfactory sensory neurons that mediate alarm responses transduce amino acids and related compounds. A laboratory assay confirmed the behavioral activity contained in the alarm cue resides in the water-soluble fraction of the skin extract. This water-soluble fraction consisted primarily of creatine (70%), heterocyclic nitrogenous compounds (4.3%) and free amino acids (18.4%), respectively. Among the free amino acids characterized in our study, essential amino acids constituted 13% of the water-soluble fraction. Free amino acids isolated from the water-soluble fraction composed of arginine, phenylalanine, threonine, and asparagine 3.9, 2.7, 2.6 and 2.4% of the water-soluble fraction, respectively. We discuss the implications of these findings for understanding the nature and use of the sea lamprey alarm cue in conservation activities.

Partial Text

Parasitic feeding by the invasive sea lamprey (Petromyzon marinus) remains the most significant source of non-fishing mortality for many fishes of the Laurentian Great Lakes and represents one of the greatest impediments to restoration of the world’s largest freshwater ecosystem. The United States and Canada currently expend more than $20 million (US) each year to suppress the invasive population by killing riverine larvae with lampricides before they metamorphose into parasites, and by maintaining dams that prevent migrating adults from entering hundreds of rivers with high-quality spawning habitat [1]. Though effective, there is considerable societal interest in reducing pesticide applications to the environment and reconnecting the Great Lakes to its tributaries via dam removal and fish passage [2]. Thus, the development and testing of new environmentally benign tactics for reducing reproductive success of the sea lamprey is a significant conservation goal [3].

The lampreys exhibited no preference response to the solvent control (proportion on the stimulus side, mean ± 2 SE, 0.501 ± 0.07; Fig 4). As predicted, migratory-phase male sea lamprey were repelled by the full skin extract (vs. solvent control, t1,18 = 6.06, P < 0.0001), and the chloroform-insoluble fraction (vs. solvent control, t1,18 = 6.83, P < 0.0001). The lampreys were not significantly repelled by the chloroform-soluble fraction (vs. solvent control, t1,18 = 1.58, P = 0.13). Behavioral reactivity was confined to the chloroform-insoluble fraction of a Soxhlet skin extract, suggesting constituents of the sea lamprey alarm cue are water-soluble nitrogenous compounds, as confirmed by detailed NMR and MS experiments, consistent with the predictions arising from the sensory physiology of fishes, including lampreys, and prior reported work with individual compounds (e.g. hypoxanthine-3-N-oxide). The most abundant component of the water-soluble fraction was creatine (70%). Other major compounds in the water-soluble fraction were heterocyclic nitrogen compounds and free amino acids, 4.3 and 18.4% of the water-soluble fraction, respectively (Table 4). We have not yet identified compounds from minor fractions yielded from the purification of major compounds from the active water-soluble fraction of the sea lamprey skin extract. This was only because of the very small quantity of these fractions yielded from a large-scale extraction and purification steps. We anticipate to complete the characterization of minor compounds in these fractions since it requires large-scale extractions and availability of animals.   Source: http://doi.org/10.1371/journal.pone.0217417