Ichthyomyzon Fossor Research Articles

Transcriptomic analysis of gonadal development in parasitic and non-parasitic lampreys (Ichthyomyzon spp.), with a comparison of genomic resources in these non-model species.

Lampreys are jawless fishes that diverged ∼550 million years ago from other vertebrates. Sequencing of the somatic and the germline genomes of the sea lamprey (Petromyzon marinus) in 2013 and 2018, respectively, has helped to improve our understanding of the genes and gene networks that control many aspects of lamprey development. However, little is known about the genetic basis of gonadal differentiation in lampreys, partly due to the prolonged period during which their gonads remain sexually indeterminate. We performed RNA-sequencing on gonadal samples from four chestnut lamprey (Ichthyomyzon castaneus) and six northern brook lamprey (I. fossor) to identify differentially expressed genes (DEG’s) and pathways associated with transcriptomic differences in: (1) larvae during early gonadal differentiation versus definitive females (i.e., with oocytes in the slow cytoplasmic growth phase); and (2) females versus definitive males undergoing spermatogonial proliferation. We compared the mapping percentages of these transcriptomes to the two available sea lamprey reference genomes and three annotation files (Ensembl and UCSC for the somatic genome and SIMRbase for the germline genome). We found that mapping the RNA-seq reads to the germline genome gave superior results and, using Trinotate, we provided new putative annotations for 8161 genes in the somatic assembly and 880 genes for the germline assembly. We identified >2000 DEG’s between stages and sexes, as well as biological pathways associated with each. Interestingly, some of the upregulated genes (e.g., DEG’s associated with spermiation) suggest that changes in gene expression can precede morphological changes by several months. In contrast, only 81 DEG’s were evident between the chestnut lamprey (that remains sexually immature during an extended post-metamorphic parasitic feeding phase) and the nonparasitic northern brook lamprey (that undergoes sexual maturation near the end of metamorphosis), but few replicates were available for comparable stages and sexes. This work lays the foundation for identifying and confirming the orthology and the function of genes involved in gonadal development in these and other lamprey species across more developmental stages.

Changes in native lamprey populations in the Great Lakes since the onset of sea lamprey (Petromyzon marinus) control

The control of invasive sea lamprey in the Great Lakes basin has been highly successful, but has deleteriously affected native lamprey species. American brook, northern brook, silver and chestnut lampreys are all susceptible to lampricide treatments. Incidental catch from surveys that targeted sea lamprey were used to determine changes in distributions and catch rates of these native species within the Great Lakes basin since the onset of the sea lamprey control program. Over 2.4 million native lampreys were collected during sea lamprey control operations between 1947 and 2018. Native lampreys were no longer captured from many treated and untreated streams. Silver lamprey and northern brook lamprey distributions were reduced most substantially. These species were no longer found in about three quarters of the number of streams in which they were historically present. The number of streams inhabited by chestnut lamprey has diminished by half. American brook lamprey were still present in the majority of streams previously occupied. Catch rates declined in northern brook lamprey and Ichthyomyzon larvae in some Great Lakes basins, but changes in collection gear and methods made comparisons difficult. Trap and weir data show drastic declines in silver lamprey and chestnut lamprey. Streams that have not been treated with lampricide have suffered similar or greater declines in both the number of streams occupied and catch rates for all four species when compared to untreated streams. Therefore reductions in native lamprey populations were likely due to a number of environmental changes, and not exclusively from lampricide treatments.

Novel “omega muscle units” in superficial body-wall myotomes during metamorphosis in the northern brook lamprey (Ichthyomyzonfossor)

Lampreys transform from sedentary filter feeders to more mobile adults through a dramatic metamorphosis that includes remodeling of head muscle and skeletal systems. Metamorphic modifications of body-wall myotomes that could support changes in swimming behavior from larvae to adults have not been previously reported. Thus, transverse sections of northern brook lamprey (Ichthyomyzon fossor Reighard and Cummins, 1916) in larval (n = 4), metamorphosing (n = 3), and adult (n = 2) stages were used to investigate the architecture of body-wall muscle and to detect whether Pax7 and MyoD, proteins important in myogenesis, were co-localized in any muscle nuclei. In addition to myotomal complexity of muscle units composed of parietal and central fibers, there was a novel pattern of omega-shaped muscle units with curves of muscle fibers in the superficial mid-body myotome in metamorphosing lamprey. Small satellite-like cells were identified on central fibers in metamorphosing and adult lamprey muscle using routine histology and immunolocalization of Pax7 and MyoD with antibodies that specifically detect mammalian and teleost proteins. Transient “omega muscle units” may be a marker for impending myotomal growth and increasing swimming efficiency during maturation, possibly restricted to metamorphosis. Finding satellite-like cells suggests that Pax7 and MyoD may have distinctive roles in lamprey myogenesis.

Stream characteristics associated with feeding type in silver (Ichthyomyzon unicuspis) and northern brook (I. fossor) lampreys and tests for phenotypic plasticity

In most lamprey genera, “paired” species exist in which the larvae are morphologically indistinguishable but adult feeding type differs. The lack of diagnostic genetic differences in many pairs has led to suggestions that they constitute a single gene pool with environmentally influenced feeding types. To investigate whether stream characteristics are correlated with feeding type in the parasitic silver lamprey Ichthyomyzon unicuspis and non-parasitic northern brook lamprey I. fossor, eight variables (pH, alkalinity, conductivity, discharge, total dissolved solids, and density of larval sea lamprey Petromyzon marinus, Ichthyomyzon spp., and total larval density) were compared among eight streams with only silver lamprey, 10 with only northern brook lamprey, and 13 with both species, using classification tree analysis. The most parsimonious model had a 24% misclassification rate, with silver lamprey tending to inhabit streams with higher sea lamprey larval density and northern brook lamprey tending to inhabit streams with higher Ichthyomyzon larval density. We then conducted a pilot study investigating phenotypic plasticity in a lab-based common garden experiment and an in situ transplant experiment. These studies encountered myriad difficulties and were unable to demonstrate plasticity, but did identify challenges associated with culturing Ichthyomyzon larvae. Development of effective rearing procedures for Ichthyomyzon lampreys is essential for any future similar studies.

Crowding reduces feeding rate, effectiveness of diet selection, and efficiency of digestion by Northern Brook Lamprey ammocetes (Ichthyomyzon fossor)

We studied the effect of larval density on food utilization by sediment-dwelling northern brook lamprey (Ichthyomyzon fossor) larvae in the Otter River, Baraga County, MI, USA using field surveys and in situ cage experiments. Field surveys found that food utilization was inversely proportional to density across the range of 1 to 10 larvae/m2. Compared to 1 larvae/m2, values at 10 larvae/m2 were lower by an average of 36% for gut fullness, by 32% for selective ingestion of organic matter, and by 71% and 58% for assimilation of diet organic matter and diet amino acids, respectively. In situ cage experiments and additional field studies in other nearby rivers revealed the same relationships. We hypothesize that physical disturbance of the sediment by adjacent larvae interferes with food utilization with the frequency of disturbance proportional to density. Condition factors were not correlated with density and indicate that individual larvae minimize the effect of crowding by moving away from higher density patches. We conclude that these findings are generalizable to other lamprey species in similar environments in which lower rates of growth, maturation, and survivorship of lamprey larvae at higher densities have been reported by other researchers.

Detection and identification of lampreys in Great Lakes streams using environmental DNA

Abstract Control of sea lamprey Petromyzon marinus in the Great Lakes requires accurate assessment of the instream distribution of this pest species and the ability to distinguish it from the four lamprey species that are native to the Great Lakes (American brook lamprey Lethenteron appendix , chestnut lamprey Ichthyomyzon castaneus , northern brook lamprey Ichthyomyzon fossor , and silver lamprey Ichthyomyzon unicuspis ). We developed PCR-based environmental DNA (eDNA) assays to distinguish among the four “genetic species” of Great Lakes lampreys (silver and northern brook lampreys were genetically indistinguishable), tested them under laboratory conditions, and demonstrated in the field that both spawning and larval sea lamprey can be detected using eDNA. In the laboratory, mean detection frequency decreased with increasing flow rate, but was not significantly related to larval density or temperature over the range of relatively high densities tested. Proof-of-concept was demonstrated in the field when sea lamprey eDNA was detected during the spawning season (when large-bodied adults, their gametes, and later their carcasses were present); sampling effort involved collection of three 1–2 L water samples at each of four transects (0.4–1.0 km apart). Mean detection frequency remained high (81–97%) until spawning ceased at the end of June, but decreased thereafter, falling to 6% by mid-August. We also demonstrated that eDNA of smaller, burrowing larvae (in water collected after mid-August) was detectable in two of four streams with medium to high larval density (1–2 larvae/m 2 ), but not at low densities ( 2 ), potentially due to the exacerbating effect of high flow rates.

An Examination of Petromyzontidae in Pennsylvania: Current Distribution and Habitat Preference of Lampreys

Abstract Native populations of lampreys are declining throughout the Great Lakes drainage basin due to habitat loss and degradation, anthropogenic stresses, and stream treatment with lampricides to control the exotic Petromyzon marinus (Sea Lamprey). We surveyed 19 streams across Pennsylvania to determine the presence/absence of six species that were historically found there. In 2011, we found four species—Lamptera aepyptera (Least Brook Lamprey), Lethenteron appendix (American Brook Lamprey), Ichthyomyzon greeleyi (Mountain Brook Lamprey), and Sea Lamprey—in 14 creeks statewide. In 2012, we found three species—Least Brook Lamprey, American Brook Lamprey, and Mountain Brook Lamprey— in 8 creeks in the Allegheny watershed. Lampreys appeared to be extirpated at some sites. Historically, Ichthyomyzon bdellium (Ohio Lamprey) and Ichthyomyzon fossor (Northern Brook Lamprey) were reported, but we did not observe these species during our study. Substrate analysis indicated ammocoetes preferred substrates with a ...

Complete mitochondrial genomes of paired species northern brook lamprey (Ichthyomyzon fossor) and silver lamprey (I. unicuspis)

The complete mitogenomes of paired species northern brook lamprey (Ichthyomyzon fossor) and silver lamprey (I. unicuspis) is reported. The two mitogenomes show a 13 bp length difference on the tRNA-Gly and two control regions. The gene order and contents are conserved in the two lampreys and identical to the lamprey mitogenomes published. Except for three indel polymorphic sites, there are 27 SNP sites which are all synonymous substitution sites and occurred on 9 protein-coding genes, two rRNAs and one tRNA. The control region1 contains six consecutive 39-nt repetitive strings in both lampreys. A 7-nt repetitive string in the control region2 is repeated 3 and 5 times in northern brook lamprey and silver lamprey, respectively. The observed level of similarity between nucleotide sequences (99.74%) is consistent with the hypothesis that northern brook lamprey and silver lamprey represent two ecotypes of one species.

Gene expression during ovarian differentiation in parasitic and non-parasitic lampreys: Implications for fecundity and life history types

Lampreys diverged from the jawed vertebrate lineage approximately 500million years ago. Lampreys undergo sex differentiation much later than most other vertebrates, and ovarian differentiation occurs several years before testicular differentiation. The genetic basis of lamprey sex differentiation is of particular interest both because of the phylogenetic importance of lampreys and because of their unusual pattern of sex differentiation. As well, differences between parasitic and non-parasitic lampreys may first become evident at ovarian differentiation. However, nothing is known about the genetic basis of ovarian differentiation in lampreys. This study examined potential differences in gene expression before, during, and after ovarian differentiation in parasitic chestnut lamprey Ichthyomyzon castaneus and non-parasitic northern brook lamprey Ichthyomyzonfossor. Eight target genes (17β-hydroxysteroid dehydrogenase, germ cell-less, estrogen receptor β, insulin-like growth factor 1 receptor, daz-associated protein 1, cytochrome c oxidase subunit III, Wilms’ tumour suppressor protein 1, and dehydrocholesterol reductase 7) were examined. Northern brook lamprey displayed higher expression of cytochrome c oxidase subunit III, whereas chestnut lamprey displayed higher expression of insulin-like growth factor 1 receptor; these genes may be involved in apoptosis and oocyte growth, respectively. Presumptive male larvae had higher expression of Wilms’ tumour suppressor protein 1, which may be involved in the undifferentiated gonad and/or later testicular development. Differentiated females had higher expression of 17β hydroxysteroid dehydrogenase and daz-associated protein 1, which may be involved in female development. This study is the first to identify genes that may be involved in ovarian differentiation and fecundity in lampreys.

Reduced fecundity in non‐parasitic lampreys may not be due to heterochronic shift in ovarian differentiation

Heterochrony is an important mechanism for the evolution of differences between and within species. In lampreys, heterochrony has been suggested as a mechanism contributing to fecundity differences in non-parasitic versus parasitic species. Non-parasitic lampreys, which do not feed at all after metamorphosis, have much smaller body sizes at maturation and therefore much lower fecundity than parasitic lampreys. Previous studies have suggested that this fecundity difference is established in the larval stage through ovarian differentiation at a younger age (and therefore smaller body size) in non-parasitic females, leading to production of fewer oocytes. The current study examined whether this pattern is applicable in two additional lamprey species. The timing of histological ovarian differentiation was determined in larval parasitic chestnut lamprey Ichthyomyzon castaneus and non-parasitic northern brook lamprey I. fossor in southeastern Manitoba, Canada, and potential fecundity was compared through oocyte counts in differentiated females of both species. Ovarian differentiation occurred in age classes 1 and 2 in both chestnut and northern brook lampreys, and there were no significant differences in the timing of ovarian differentiation between species; this indicates that the timing of ovarian differentiation is not a reliable marker of life history type. Factors such as growth and body condition may determine whether an individual undergoes ovarian differentiation in age class 1 or 2. Chestnut and northern brook lampreys had similar minimum oocyte counts; however, the average and maximum oocyte counts were higher in chestnut lamprey in each age class. As the timing of ovarian differentiation is similar in chestnut and northern brook lampreys, the higher potential fecundity of chestnut lamprey must originate through mechanisms other than heterochrony.

Contemporary gene flow between “paired” silver (Ichthyomyzon unicuspis) and northern brook (I. fossor) lampreys: implications for conservation

In most lamprey genera, “paired” species exist in which the larvae are morphologically similar or indistinguishable but, following metamorphosis, one species becomes parasitic while the other bypasses the adult feeding phase and rapidly becomes sexually mature. Since DNA barcoding and similar studies using short segments of the mitochondrial genome do not provide sufficient resolution to distinguish between recent divergence and a lack thereof, the current study examined the relationship between the parasitic silver lamprey (Ichthyomyzon unicuspis) and nonparasitic northern brook lamprey (I. fossor) using up to 10,230 bp from the mitochondrial genome to make phylogenetic inferences and mitochondrial restriction fragment length polymorphism (RFLP) and microsatellite markers to test for significant differences in allele frequencies. We found that silver and northern brook lampreys are not reciprocally monophyletic; two lineages were observed but each occurred within both species. There also were no significant range-wide differences in RFLP haplotype or microsatellite allele frequencies between the species, nor were there significant differences where they occurred sympatrically within the Lake Huron basin. Significant genetic differentiation was found only within the Lake Michigan basin where the results were potentially confounded by geographic separation. Our results thus support suggestions that silver and northern brook lampreys represent ecotypes of a single species since, where they are sympatric, they appear to be experiencing ongoing gene flow. However, alternative life history strategies can be important for a species’ long-term persistence, and critical data are needed to decide whether these two feeding types should be managed as a single unit.

Characterization of 14 microsatellite loci in the paired lamprey species Ichthyomyzon unicuspis and I. fossor and cross amplification in four other Ichthyomyzon species

We describe the isolation and development of 14 polymorphic microsatellite loci in silver lamprey (Ichthyomyzon unicuspis). The number of alleles ranged from 2 to 11 (with an average of 5.1 alleles per locus) in 23–37 lampreys and genetic diversity ranged from 0.036 to 0.837. All of these loci were also polymorphic (with 2–10 alleles, average 4.4) in the closely related northern brook lamprey (I. fossor), and at least eight were polymorphic in four other Ichthyomyzon species. These loci will aid in studying the population dynamics of these six Ichthyomyzon species.

An attempt to differentiate sympatricIchthyomyzonammocoetes using meristic, morphological, pigmentation, and gonad analyses

We assessed characters that could be used to differentiate ammocoetes of chestnut lamprey ( Ichthyomyzon castaneus Girard, 1858), northern brook lamprey ( Ichthyomyzon fossor Reighard and Cummins, 1916), and silver lamprey ( Ichthyomyzon unicuspis Hubbs and Trautman, 1937). We sampled ammocoetes of the three species from 25 streams around the Great Lakes. Existing genetic markers were used to identify chestnut lamprey for this study, but the lack of genetic markers for silver and northern brook lampreys forced our preliminary classification of these two species to be based on stream-specific catch records of adults. Comparison of ammocoete gonads was inconclusive as a technique to distinguish between these two species. Other characters examined (including pigmentation patterns, morphometric characters, body shape, and myomere counts) varied significantly among species, but were inadequate for use as diagnostic characters because of high intraspecific variation and overlapping ranges. Chestnut lamprey ammocoetes were sometimes distinguishable by their pigmented lateral line organs, but this character was not always apparent. The lack of distinguishing characteristics makes existing taxonomic keys misleading for identifying Ichthyomyzon lamprey larvae.

Discriminating Lamprey Species Using Multilocus Microsatellite Genotypes

AbstractEfforts to manage the invasive sea lamprey Petromyzon marinus in the Great Lakes have greatly reduced the species' abundance and distribution. The methods employed have also affected the abundance and distribution of species that are native to the Great Lakes basin, including the American brook lamprey Lampetra appendix (also known as Lethenteron appendix), the northern brook lamprey Ichthyomyzon fossor, and the silver lamprey I. unicuspis. Discrimination among the four species based on the phenotypic characteristics of larvae is difficult, making accurate assessments of their abundance, recruitment, and distribution within streams problematic. Given growing interest in the conservation of native species and the effects of sea lamprey controls, an alternative method of identification is warranted. Owing to species‐specific fixed differences in alleles, microsatellite loci were extremely useful in discriminating lamprey species. Samples of each species were analyzed with respect to seven microsatellite loci. Based on the genetic differences among individuals, we were able to separate samples of each species by genus. In addition, brook and silver lampreys could be identified to species with high probability. Assignment tests of Ichthyomyzon species revealed a confidence of assignment of at least 0.95 for 96.4% of all individuals. Using a single locus, we examined larvae of a single cohort when larval size was consistent with age‐0 (n = 449) and age‐1 (n = 1,203) status across five Lake Superior streams. When genotyped using a discriminating locus, it was found that 57.9% of those that were age 0 and 16.8% of those that were age 1 were incorrectly identified based on phenotype. Within one stream, we observed significant differences in the distributions of native and sea lamprey larvae across upstream, middle, and downstream regions, suggesting that there are species differences in spawning sites and focal areas of larval recruitment. Molecular methods will prove to be a useful tool in assessing native species' abundance and distribution and can direct management to the application of alternative control methods.

Feeding by Northern Brook Lamprey ( Ichthyomyzon fossor) on Sestonic Biofilm Fragments: Habitat Selection Results in Ingestion of a Higher Quality Diet

This study examined interrelationships among habitat type, selective feeding, diet quality, assimilation efficiency, and condition in larval northern brook lamprey ( Ichthyomyzon fossor) in three lower order streams in Michigan's Upper Peninsula. Larvae were less abundant in sand (site means = 0.2 to 0.5 larvae / 2,500 cm 2) than in organic sediment (0.5 to 2.85 / 2,500 cm 2). Within patches of organic sediment, larvae aggregated at sites where obstacles to flow caused localized accumulation of flocculent material (≤ 26 larvae / 2,500 cm 2). Ingestion was selective, with both amino acid and total organic matter higher in foreguts than in seston. Habitat type selected by a larva had relatively minor consequences for organic matter and amino acids in the diet, but had major consequences for assimilation efficiency for both nutrients with highest efficiencies in depositional areas where larvae aggregated. Condition factors (weight per length) were similarly highest in these depositional areas. Variation in diet composition over time suggests an annual cycle of seston production resulting from biofilm sloughing from solid surfaces as controlled by stream discharge and the availability of light to support algal production.

Trace Metal Levels in Benthic Biota from Four Tributaries to the St. Lawrence River, Quebec

Abstract Lamprey ammocoetes (Agnatha: Petromyzontidae) and freshwater mussels (Bivalvia: Unionidae), two groups of organisms that are closely associated with sediments, were collected from the Châteauguay, Bécancour, Sainte-Anne and Saint-Maurice rivers in July 1992 and analyzed for residues of 13 metals in their tissues. The hypothesis that lamprey larvae and mussels would bioaccumulate comparable levels of metals due to similarities in their ecology was rejected. Lampreys (Ichthyomyzon fossor and Lampetra appendix) from the Châteauguay River (the only site where both lampreys and mussels were collected) accumulated significantly lower concentrations of Ag, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Tl, V and Zn than mussels (Elliptio complanata), suggesting that lampreys may be capable of regulating these metals. Conversely, lampreys accumulated much higher concentrations of Hg than mussels (1748 to 6793 versus 579 to 982 ng/g dry weight, respectively), indicating that they may be suitable biomonitors for Hg. Organisms that are capable of regulating metals are not normally recommended for biomonitoring purposes. Nevertheless, significant differences among rivers were observed for many metals based on the lamprey data. As metals in the gut contents of three specimens of Sea lamprey (Petromyzon mar-inus) from the Saint-Maurice River accounted for a substantial portion of the whole body burden of metals, a gut content correction factor is recommended for these organisms. Further studies are required to properly evaluate lamprey ammocoetes as biomonitors for trace metals in freshwater systems.

Trace metals in fluid-preserved museum fish specimens

This paper describes the effects of preservation on the trace metal levels in the larvae of four lamprey species, Petromyzon marinus, Ichthyomyzon fossor, I. unicuspis and Lampetra appendix, collected between 1946 and 1951 from three tributaries of the St. Lawrence River Basin, Québec. Contrary to most other studies on the subject, this study rejects the usefulness of using fluid-preserved museum fish specimens in retrospective monitoring of trace metal levels in the aquatic environment because the many sources of contamination cannot be accurately measured.

Significance of Organic Detritus in the Diet of Larval Lampreys in the Great Lakes Basin

Larval sea lamprey (Petromyzon marinus) and northern brook lamprey (Ichthyomyzon fossor) were collected monthly from three streams in the Upper Peninsula of Michigan from May 1992 through May 1993 and larval sea lampreys were collected during summer months from sites throughout the Great Lakes basin. Organic detritus made up most of the diet ash-free-dry-mass (AFDM) throughout the year, averaging 97.79%, with algae (2.12%) and bacteria (0.09%) making up the remainder of the diet AFDM. Assimilation efficiency for AFDM averaged 72% during warmer months and 53% during cooler months (annual mean = 61%). Gut fullness (amount of AFDM in the anterior one-tenth of the intestine) was low (mean = 0.10 mg diet AFDM∙g−1ammocoete). There were no significant differences in these measures between ammocoetes collected from the Upper Peninsula and those collected throughout the Great Lakes basin. From a laboratory-determined relationship between gut fullness and feeding rate, feeding rate in the field was estimated to be extremely slow, ranging from 4.2 to 5.5 mg diet AFDM∙g−1ammocoete∙d−1. These observations indicate that larval lampreys efficiently utilize a diet of organic detritus during warmer months when stream temperatures and food quality are more favorable for feeding, digestion, and growth.

Changes in the Distribution of Native Lampreys in Lake Superior Tributaries in Response to Sea Lamprey (Petromyzon marinus) Control, 1953–77

Populations of three species of lampreys, American brook lamprey (Lampetra lamottei), northern brook lamprey (Ichthyomyzon fossor), and silver lamprey (I. unicuspis), endemic to the Lake Superior drainage basin have declined since chemical control of the sea lamprey (Petromyzon marinus) was begun; 64% (103 of 162) of the streams inhabited by endemic species have required treatment. The parasitic silver lamprey was most adversely affected by lampricide applications. Though 4278 were captured at 35 of 55 Lake Superior barriers in 1959, a total of 91 were reported in only nine tributaries and the St. Marys River from 1973 to 1977. American brook lampreys were least affected by chemical control and have disappeared from 6 of 42 treated streams which they inhabited. Ichthyomyzon larvae are no longer found in 41 of 81 treated streams they once inhabited, though few larvae were found in many of these streams. Several factors affected the vulnerability of native lampreys to chemicals. Nonparasitic lampreys, especially American brook lampreys, inhabited headwater areas which were often not invaded by sea lampreys, but silver lampreys spawned in lower reaches and their entire stream distribution was exposed to the effects of the lampricide. Differences in fecundity of lampreys also affected their recovery after chemical treatments.Key words: Ichthyomyzon fossor, ichthyomyzon unicuspis, Lampetra lamottei, streams, distribution, habitat, temperature, fecundity, survival, TFM

Lethal Temperatures in Ammocoetes of Four Species of Lampreys

An investigation has been made of the resistance time and upper lethal temperature of ammocoetes of four species of lampreys provided with a substrate into which they could readily burrow. In general, ammocoetes burrowed after transfer from the acclimation to the experimental temperature baths and later came out of the substrate only in lethal temperatures. A relationship was observed between the resistance time and the time taken to emerge, with the resistance time increasing exponentially with decreasing experimental temperature. In Ichthyomyzon fossor, landlocked Petromyzon marinus, Lampetra (Lethenteron) Lamottenii and in Lampetra (Lampetra) planeri from two different times of the year, the incipient lethal levels over a two week experimental period for larvae acclimated to 15° G were respectively 30.5, 30, 29.5, 28.5 and 28° C. Values for P. marinus acclimated to 5 and 25° C were respectively 29.5 and 31° C, whereas in L. planeri they were 28 and 29° C in April/May and 27 and 29° C in July/August. Extrapolation of the results for the three acclimation temperatures yielded ultimate incipient lethal levels of 31.4° G in P. marinus and 29.2 and 29.4° C for L. planeri examined in the spring and summer respectively.