Four behavioral experiments conducted in both the laboratory and the field provide evidence that adult sea lamprey (Petromyzon marinus) select spawning rivers based on the odor of larvae that they contain and that bile acids released by the larvae are part of this pheromonal odor. First, when tested in a recirculating maze, migratory adult lamprey spent more time in water scented with larvae. However, when fully mature, adults lost their responsiveness to larvae and preferred instead the odor of mature individuals. Second, when tested in a flowing stream, migratory adults swam upstream more actively when the water was scented with larvae. Third, when migratory adults were tested in a laboratory maze containing still water, they exhibited enhanced swimming activity in the presence of a 0.1 nM concentration of the two unique bile acids released by larvae and detected by adult lamprey. Fourth, when adults were exposed to this bile acid mixture within flowing waters, they actively swam into it. Taken together, these data suggest that adult lamprey use a bile acid based larval pheromone to help them locate spawning rivers and that responsiveness to this cue is influenced by current flow, maturity, and time of day. Although the precise identity and function of the larval pheromone remain to be fully elucidated, we believe that this cue will ultimately prove useful as an attractant in sea lamprey control.

Recently metamorphosed sea lampreys Petromyzon marinus were captured in the Devil River, a tributary to Lake Huron, during summer and autumn 1990. They were tagged with a coded wire tag and returned to the river to continue their migration to Lake Huron to begin the parasitic (juvenile) phase of their life. During the spawning run in spring 1992 when the tagged animals were expected to mature and return to spawn, sea lampreys were trapped in nine tributaries to Lake Huron, including the Devil River; 47,946 animals were examined for coded wire tags, and 41 tagged animals were recovered. None of the 45 mature sea lampreys captured in the Devil River in 1992 were tagged, a proportion (0%) significantly lower than the proportion of the recently metamorphosed sea lampreys tagged in 1990. The distribution of tag recoveries among streams lakewide, however, was proportional to catch. Tagged sea lampreys did not appear to home, but instead seemed to select spawning streams through innate attraction to other sensory cues.

Populations of Pacific lamprey Lampetra tridentata have declined in the Columbia River basin. One factor that may have contributed to this reduction in population size is an excessive use of energy by adult lampreys as they negotiate fishways at dams during spawning migrations. To gain an understanding of the performance capacity of Pacific lampreys, we estimated the critical swimming speed (Ucrit) and documented physiological responses of radio‐tagged and untagged adult lampreys exercised to exhaustion. The mean (±SD) Ucrit of untagged lampreys was 86.2 ± 7.5 cm/s at 15°C, whereas the Ucrit for radio‐tagged lampreys was 81.5 ± 7.0 cm/s, a speed that was significantly lower than that of untagged fish. The physiological responses of tagged and untagged lampreys subjected to exhaustive exercise included decreases in blood pH of 0.3–0.5 units, a 40% decrease in muscle glycogen levels, a 22% increase in hematocrit for untagged fish only, and a 4‐ to 5‐fold increase in muscle and a 40‐ to 100‐fold increase in plasma lactate concentrations. These physiological changes were significant compared with resting control fish and usually returned to resting levels by 1–4 h after fatigue. Our estimates of Ucrit for Pacific lampreys are the first quantitative measures of their swimming performance and suggest that these fish may have difficulty negotiating fishways at dams on the Columbia River, which can have water velocities approaching 2 m/s. Our physiological results indicate that tagged and untagged Pacific lampreys show similar metabolic dysfunction after exhaustive exercise but recover quickly from a single exposure to such a stressor.

No abstract

Importance of condition factor and the influence of water temperature and photoperiod on metamorphosis of sea lamprey, Petromyzon marinus. Can. j. Fish. Aquat. Sci. 58: 2448-2456.The incidence of metamorphosis of larval sea lamprey, Petromyzon marinus, was strongly affected by water temperature but not photoperiod. In a 1991 experiment, the development of metamorphosing anirnals in 13°C water was retarded about 1 mo relative to animals metamorphosing at 21 "C and to a population from the Chippetva River, Michigan; the minimum length, weight, and condition factor (CF) of metamorphosing experimental animals were 11 7 mm, 2.8 g, and 1.50, respectively, and only 4% metamorphosed at 13°C and 18.9% at 21 "C. In 1992, with a population from the Great Chazy River, New York, 66% of the animals at 13°C and 84% at 21 "C metamorphosed. The higher incidence of metamorphosis in 1992 is partly related to the use of larvae that were larger than the minima established in 1991. We predicted, using criteria defined below, that 74 and 72% of the animals at 13 and 21 "C, respectively, would metamorphose. Our predictions were consistent with observations at 13°C and for five of seven replicate tanks at 21 "C. We suggest that a presumptive metamorphosing sea lamprey in landlocked populations should be at least 120 mrn long, weigh 3.0 g, and have a CF 2 1.58 and that these criteria must be used in conjunction. L'apparition de la metamorphose des larves de la grande lamproie marine, Petromyzon marinus, etait forternent touchee par la tempkrature de I'eau, mais pas par la photoperiode. Lors d'une experience menee en 1991, If6volletion de la metamorphose des anirnaux dans de I'eau & 13 "C a kt6 retardee de 1 mo environ par rapport aux animaux qui se m6tarnorphosaitdans de I'eau a 21 "C et Bsne population de la rivigre Chippewa, Michigan; ia longueur minimale, le poids et le coefficient de condition des animaux subissant une mktarnorphose exp6rimentale btaient respectivernent de 11 7 mm, 2,8 get 1/50 et seulement 4 % des animaux se sont metamorphoses 2 13 "C et 18,9 [YO a 21 "C. En 1992, dans le cas d'une population de Is rivi&re Great Chary, New York, 66 % des animaux se sont rn6tarnorphosks 21 13 "C et 84 O/ O 2 21 'C. La frequence plus 4lev6e de m6tamorphose Fn 1992 est %iee en partie I'utilisation de larves qui 6taient plus grosses que la tailie minimale etablie en 1991. A partir des critPres dkfinis ci-dessous, nous prkvoyons que respectivement 74 et 72 % des animaux placbs respectivement dans de I'eau A 13 et 21 "C se rnetamorphoseront. Nos previsions etaient conforrnes aux observations effectuees 2 13 "C et pour cinq des sept bassiws dr6tude 3 21 "C. Selon nous, dans des populations dulcicoles, une grande lamproie marine entamerait sa rn6tamorphose 3 moins 120 mrn de longueur, pour un poids de 3,0 g et avec un coefficient de condition de 1,5Q et que ces criteres devraient &re utilises ccsnjointement.