Radioisotope and stable isotope ratios (Δ14C, δ15N) suggest larval lamprey growth is dependent on both fresh and aged organic matter in streams

Lampreys have a complex life cycle which includes a multi‐year infaunal larval stage (ammocoete). Gut content analysis has generally identified detritus (i.e., unidentifiable organic matter) as the major dietary component to ammocoetes, though algae can also be important. However, gut content preserves only a snapshot of the animal's diet and does not reflect assimilated material. In order to better characterise the nutritional sources supporting ammocoete growth, we analysed ammocoete body tissue and potential dietary sources at two streams using natural Δ¹⁴C and δ¹⁵N to estimate time‐integrated nutritional support. Bayesian isotope mixing models revealed differences in the importance of sources supporting ammocoetes between sites. Ammocoetes from a stream in a mixed land usage area (~50% agriculture, ~40% forest and ~10% developed) were primarily supported (mean: ~50%) by fresh terrestrial organic matter but were also supported by substantial contributions (mean: ~30%) by aged organic matter (AOM) and autochthonous material (algae; mean ~20%). In a predominantly forested (~90%) headwater stream, different modelling scenarios (uninformed or informed priors) suggested that algal support of ammocoete nutrition ranged from 7% to 45%. However, the model relying on informed priors developed from gut content analysis produced the low estimates, suggesting these were more reliable. When algae were a minor component of the nutrition at the forested site, ammocoetes were highly dependent on AOM (83 ± 26%; mean ± SD). Based on these findings, ammocoete growth and development are predicted to be strongly influenced by both land use and the availability of allochthonous and autochthonous materials of varying ages within streams.     

Distribution, growth and transformation timing of larval Geotria australis in New Zealand

Lamprey, Geotria australis, are widely distributed in New Zealand and are common in streams and rivers of the west coast of both islands, the southern tip of the North Island, the Banks Peninsula and the southern coast of the South Island. In fresh water, lamprey are found in association with all substrate types but are most commonly (> 50% of the sample sites) found in association with finer gravels. There is insufficient evidence to determine any change in historically abundant adult spawning migrations. Spawning, back calculated from larval growth rates, probably occurs late November-December, and emergence at 9.63 mm occurs in January. We estimate that, on average, ammocoetes grow 0.068 mm/day throughout the year, and metamorphose and emigrate to sea between January-May, 3.5 years after spawning at 101 mm (SD = 6.7).     

Development of diets for the intensive culture of Pacific lamprey

The Pacific lamprey Entosphenus tridentatus is an ancestral species of critical importance to the ecosystem and indigenous cultures in the Pacific Northwest. Conservation aquaculture has been proposed as a potential technique to restore Pacific lamprey populations. Intensive culture methods and diets for this species have not been developed. A sixteen week feeding trial tested the effects of seven diet treatments on the survival, growth, fatty acid profile and whole body lipid content of Pacific lamprey ammocoetes. Dietary treatments were: active dry yeast, yeast plus fish oil emulsion, micro‐algae, micro‐algae plus fish oil emulsion, yeast with micro‐algae, yeast with micro‐algae plus fish oil emulsion and yeast with larval fish diet. Each diet was offered to five replicate tanks stocked with 20 ammocoetes that were 51 days post hatch. Survival during the trial was not affected by diet. The greatest length and weight increases were in fish fed diets containing yeast. Growth decreased as the amount of algae in the diet was increased. Lipid retention was significantly higher in fish fed yeast with larval fish diet relative to the other treatments. Feed conversion ratio was lowest in fish fed diets containing yeast. Whole body fatty acid profiles tended to reflect the fatty acid profile of the diet. Percentages of 20:5n‐3 and 22:6n‐3 were significantly higher in fish fed diets containing fish oil emulsion. Overall, yeast with larval fish diet provided the best growth performance in larval Pacific lamprey.     

Are lampreys homebodies? Studying ammocoetes with open population models

Larval lampreys (ammocoetes) are assumed to be sedentary and have restricted movements, but their movement is still poorly understood. Using elastomer implants, ammocoetes of two different species of lampreys (Lethenteron appendix and Petromyzon marinus) in two streams were tagged with permanent, unique marks (N = 1035) and resampled once a month from June 2014 until October 2014. Some individuals were recaptured during every sampling event (N = 3, 0.3%). However, most animals were never recaptured after being tagged (N = 700, 67%) or were captured only once (N = 213, 21%). The apparent survival (?) varied in response to time and grouping variables at both sites (0.25–0.86), but the probability of capture (P) did not vary as much (0.41–0.85). Differences were detected between sites, with ? being higher for L. appendix at Dyke Creek, a Genesee River tributary. Whether differences were caused by site‐specific details or species differences is unclear. At Dyke Creek, where age could be partially established from length‐frequency histograms, ? was higher for 1 year old than for older animals. At Oquaga Creek (where P. marinus were captured), ? was highly variable (0.11–0.72) and was lowest in the fall sampling (September–October). The P was similar at both sites (0.5–0.6) and across times and groups, even when it was significant to the model. Understanding the movement of ammocoetes will help conserve and control lampreys.     

Early development of Lamprey Lampetra japonica (Martens, 1868)

Studies of lamprey early development have produced major insights into primitive developmental patterns and the evolution of vertebrates. In this study, the effectiveness of the morphological and histological characteristics of Lampetra japonica during embryological, yolk‐sac larval and ammocoete stages were examined. Based on the external and histological morphology, the embryological phase was divided into eight stages, including the zygote, cleavage, blastula, gastrula, neural plate and groove, head protrusion, prehatching and hatching stages. A set of key morphological and histological transformations occurred through the yolk‐sac larval stage, reflecting the larva‐ammocoete transition. In the ammocoete stage, all organ systems were differentiated. Except for the melanophores, the lamprey did not develop any further morphological complexity beyond the ammocoete stage. The total length and body weight of larva and ammocoete generally increased over time. We hope that this study might form the basis for future studies of the phylogenetic development of this interesting group of animals.     

Laboratory assessment of sea lamprey larvae burrowing performance

Abstract –  To study the burrowing behaviour and performance of larval sea lamprey ( Petromyzon marinus L.), 120 ammocoetes were collected and observed in the laboratory. Burrowing movements of ammocoetes placed in an aquarium with sediments of differing grain size were video recorded. The video was reviewed and, for each larva, the total time spent moving, the number of stops during the burrowing movement, the total time spent stopped and total time elapsed until complete withdrawal below the substrate surface was registered. Smaller ammocoetes had lower burrowing performance than larger individuals, across all substrate types, but the differences were greater in coarser substrates. Additionally, coarser sediment particles increased the time spent on burrowing regardless of larval size.     

Distribution, larval stage duration and growth of the sea lamprey ammocoetes, Petromyzon marinus L., in a highly modified river basin

Abstract  – Larval stage duration of the sea lamprey, Petromyzon marinus , in the River Mondego is estimated to last for 4 years. The number of annuli provides reliable age estimates when compared with length–frequency distributions analysis. The growth rate of the sea lamprey ammocoetes displays strong seasonal patterns, and reaches its highest value during the first 2 years of larval stage. About 69% of the length increment between hatching and metamorphosis is attained at the end of the second year. There is a longitudinal gradient associated with ammocoete distribution along the river. Relative abundance of ammocoetes decreases downstream from the Açude-Ponte dam, the first obstruction encountered by the adult sea lampreys in their upstream spawning migration along the River Mondego.