A study of some acid hydrolases in the liver of the larval and adult lamprey

Summary The authors studied the behaviour of two acid hydrolases (phosphatase and proteinase) in the liver of the larval form (ammocoetes), of the starved larva, and of the adult lamprey (Lampetra zanandreai, Vladykov). In the homogenates of liver of ammocoetes in 0.25 M sucrose the enzymatic activities are largely sedimentable (phosphatase 67%; proteinase 56%). In the starved ammocoetes and in the adult lamprey the percentage of sedimentable activity gradually falls (phosphatase 46% and proteinase 52% in the starved ammocoetes; phosphatase 44% and proteinase 49% in the adult lamprey) whilst there is a corresponding gradual increase in free activity (phosphatase: from 24% in the normal ammocoetes to 39% in the starved ammocoetes and 50% in the adult lamprey; proteinase: from 25% in the normal ammocoetes to 35% in the starved ammocoetes and 54% in the adult lamprey). The action of detergent Triton X-100 causes an equal distribution of hydrolases activity in the three conditions of the liver.Only 25% of the sedimentable acid glycerophosphatase is accessible to the substrate in the ammocoetes, whilst in the starved ammocoetes and in the adult lamprey accessibility rises to 80%.The results we have discussed show that at metamorphosis and during fasting the lysosomes undergo such changes as to determine an actual intracellular release of the acid hydrolases studied.This work is dedicated to the memory of Prof. Giuseppe Zanandrea S. J., who greatly helped us with his advice.     

Muscle glycogen, lactate and glycerol-3-phosphate concentrations of larval and young adult lampreys in response to exercise

When stimulated, the ammocoetes (larvae) of Geotria australis swim continuously at a moderate rate for only approximately 20 min, whereas the downstream migrants (young adults) of this species did not become exhausted following similar swimming activity over the same period. Mean concentrations of muscle glycogen in ammocoetes declined during exercise, but returned to resting levels within 30 min of recovery, whereas those in young adults changed little during the corresponding periods. Moreover, muscle lactate concentrations of ammocoetes rose markedly during exercise and the first 30 min of recovery, before declining significantly, while those of young adults remained similar during and immediately after exercise. Calculations, using the glycogen and lactate concentrations immediately after exercise, suggest that during exercise glycogen is, to some extent, utilised anaerobically (approx. 24%) by ammocoetes, but only aerobically by young adults. Furthermore, since young adults used only a small amount of glycogen, they presumably metabolised triacylglycerol aerobically to produce energy. Muscle glycerol-3-phosphate levels were far higher prior to and immediately after exercise in downstream migrants than in ammocoetes and then declined precipitously. The above trends in muscle glycogen and lactate of larval G. australis parallels, to some degree, those recorded by other workers for upstream migrant Petromyzon marinus that had been exercised to exhaustion.     

Variations of life history strategy of the arctic lamprey <Emphasis Type="Italic">Lethenteron camtschaticum</Emphasis> from the Utkholok River (Western Kamchatka)

Morphobiological traits of the lamprey from the Utkholok River (Western Kamchatka) are investigated for the first time. All present forms of lamprey (typically anadromous, anadromous early maturing forma praecox, resident) do not differ by diagnostic characters and belong to one species Lethenteron camtschaticum. Males prevail among mature specimens of various forms, smolts, and ammocoetes at later developmental stages. The forma praecox is represented by males by 92%. A hypothesis is suggested explaining the relationships of the forms and the mechanism of realization of different types of life history strategy in relation to energy resources of water bodies and the kind of feeding of different groups of ammocoetes (organic detritus or Pacific salmon carcasses decomposed after spawning).     

Using stable isotopes and C:N ratios to examine the life‐history strategies and nutritional sources of larval lampreys

Natural abundance stable‐isotope analysis (δ¹³C and δ¹⁵N) and C:N ratios were used to study the ammocoete phase of two common non‐parasitic lamprey species (least brook lamprey Lampetra aepyptera and American brook lamprey Lethenteron appendix) in two tributaries of the Ohio River (U.S.A.). The C:N ratios suggest that each species employs different lipid accumulation strategies to support its metamorphosis and recruitment into an adult animal. Ammocoete δ¹³C values generally increased with increasing C:N values. In contrast to δ¹³C, ammocoete δ¹⁵N values were weakly related to the total length (L_T) in L. aepyptera, but positively correlated to both L_T and C:N ratios in L. appendix. In L. appendix, C:N also correlated positively with L_T, and presumably age. A Bayesian mixing model using δ¹³C and δ¹⁵N was used to estimate nutritional subsidies of different potential food resources to ammocoetes at each site. The models suggested that although nutritional subsidies to ammocoetes varied as a function of site, ammocoetes were generally reliant on large contributions (42–62% at three sites) from aquatic plants. Contributions from aquatic sediment organic matter were also important at all sites (32–63%) for ammocoetes, with terrestrially derived plant materials contributing smaller amounts (4‐33%). These findings provide important insights into the feeding ecology and nutrition of two species of lampreys. They also suggest that similar and other quantitative approaches are required to (1) fully understand how the observed stable‐isotopes ratios are established in ammocoetes and (2) better assess ammocoete nutritional subsidies in different natal streams.     

Morphological analysis of geographic variation of sea lamprey ammocoetes in Portuguese river basins

The main objective of this study was to compare the morphological variability of sea lamprey (Petromyzon marinus L.) larvae from the main Portuguese river basins. Samples were collected in rivers Minho, Lima, Cávado, Vouga, Mondego, Tejo and Guadiana. Specimens were analysed in terms of morphometric (linear body measures) and meristic (number of myomeres) characters to investigate the hypothesis of population fragmentation between river basins caused by some degree of homing behaviour. The discriminant analysis showed a morphological segregation of the studied populations based on the characters head, tail and branchial length. The discriminatory power of the meristic characters was comparatively weaker, with the number of trunk myomeres, and to some extent the head myomeres, being responsible for the reduced separation between groups. Both analyses were consistent in identifying the cephalic region as the most important morphological feature to discriminate populations of sea lamprey larvae in the Portuguese territory. The largest cephalic region of the ammocoetes sampled in the northern river basins may be responsible for a better feeding efficiency and, consequently, higher values of condition factor. Guest editors: S. Dufour, E. Prévost, E. Rochard & P. Williot Fish and diadromy in Europe (ecology, management, conservation)     

Oxygen consumption by ammocoetes of the lampreyGeotria australis in air

 When covered by moistened lint-free gauze, the larvae (ammocoetes) of the lamprey Geotria australis survived, without apparent discomfort, for 4 days in water-saturated air at 10, 15 and 20 °C. In air, the mean standard rates of O₂ consumption of medium to large ammocoetes of G. australis (xˉ=0.52 g) at 10, 15 and 20 °C were 14.5, 35.7 and 52.1 μl⋅g^-1⋅h^-1, respectively. At 15 °C, the slope of the relationship between log O₂ consumption (μl O₂⋅h^-1) and log body weight for ammocoetes over a wide range in body weight was 0.987. The Q ₁₀s for rate of O₂ consumption between 10 and 15 °C, 15 and 20 °C and 10 and 20 °C were 4.9, 2.9 and 3.6, respectively. Our results and observations of the ammocoetes suggest that, when out of water, larval G. australis derives most of its O₂ requirements from cutaneous respiration, particularly at lower temperatures. This would be facilitated by the small size and elongate shape (and thus a relatively high surface-to-volume ratio), low metabolic rate, thin dermis, extensive subdermal capillary network and high haemoglobin concentration of larval G. australis. Accepted: 28 March 1996     

Selection and preference of benthic habitat by small and large ammocoetes of the least brook lamprey (<Emphasis Type="Italic">Lampetra aepyptera</Emphasis>)

In this laboratory study, we quantified substrate selection by small (<50 mm) and large (100–150 mm) ammocoetes of the least brook lamprey (Lampetra aepyptera). In aquaria, ammocoetes were given a choice to burrow into six equally-available substrate types: small gravel (2.360–4.750 mm), coarse sand (0.500–1.400 mm), fine sand (0.125–0.500 mm), organic substrate (approximately 70% decomposing leaves/stems and organic sediment particles, and 30% silt and fine sand), an even mixture of silt, clay, and fine sand, and silt/clay (<0.063 mm). Fine sand was selected with a significantly higher probability than any other substrate. Fine sand habitat is limited in many streams, in part owing to geology, but also as a result of channelization and excessive silt/clay sedimentation, which is a conservation concern. Our results indicate that ammocoetes of least brook lampreys are habitat specialists that prefer fine sand habitat. Hence, availability of fine sand habitat may limit distributions and population sizes.     

Morphology of the gills of larval and parasitic adult sea lamprey,Petromyzon marinus L.

The general morphology of the gills is similar in larval (ammocoetes) and parasitic adult sea lampreys, Petromyzon marinus, despite different methods of ventilation necessitated by their feeding habits. The gill lamellae are supported by randomly-distributed pillar cells which enclose blood spaces and collagen columns. The distribution of these cells in lampreys is different from that of higher fishes and it may be inefficient for respiratory exchange. The presence of cytoplasmic microfilaments suggests that these cells have the ability to reduce the lamellar blood spaces through contraction. Marginal channels at the tips of the lamellae are lined only by endothelial cells. The thickness of the water-blood pathway in lampreys falls within the range described for higher fishes, with the most efficient gas exchange likely occurring at the lamellar tips where only a single layer of epithelial cells is present. The abrupt increase in height of the epithelium near the lamellar bases in adults, compared to the gradual transition in height along the lamellae in ammocoetes, is perhaps reflective of higher oxygen requirements during the parasitic stage. The consistent appearance of wide, lateral intercellular spaces within the respiratory epithelium of lampreys indicates possible involvement of these spaces in transport. Mucous secretion appears to be an important function of the superficial platelet cells in ammocoetes. “Mitochondria-rich” and “mitochondria-poor” superficial cells are observed in both ammocoetes and adults, with the mitochondria-rich cells more prevalent toward the lamellar bases. The possibility that at least some of these cells may be involved in absorption is discussed. Mitochondria-rich cells in the interlamellar region are morphologically different in ammocoetes and adults but all possess an abundance of smooth endoplasmic reticulum and hence resemble “chloride cells” of higher fishes. The similarity of these cells in the parasitic adult lamprey to chloride cells of marine fishes may reflect the potential of the adult lamprey to osmoregulate in salt water. A scarcity of these cells in ammocoetes and their resemblance to chloride cells in freshwater fishes may reflect the restriction of larval lampreys to a freshwater habitat.     

Capture and collection of lampreys: the state of the science

The need for native lamprey conservation, improved lamprey fishery management, and better assessment of non-indigenous lamprey control measures has resulted in increased effort to survey lamprey populations and assess their status. Depending on the study objectives and target species/life stage, collection methods vary dramatically. We therefore provide a comprehensive review of sampling considerations and techniques used to capture, collect, handle, and enumerate both juvenile and adult lamprey life stages. Surveys for lamprey are often constrained by the lack of basic biological information, such as reliable characters for field identification of larvae (ammocoetes), migratory timing of anadromous forms, and spawning/nest building behavior of adults. However, there are a number of studies that have documented habitat preferences of the relatively sedentary ammocoetes. Consequently, existing sampling protocols have focused on the development of stratified sampling that targets optimal ammocoete habitat. In addition to this approach, we discuss methods and gear that can be used to survey migratory life stages, lamprey nests, and difficult-to-sample, deepwater ammocoete habitats.     

Downstream migration in ammocoetes of the Arctic lamprey <Emphasis Type="Italic">Lethenteron camtschaticum</Emphasis> in some Kamchatka rivers

This paper considers the major patterns of downstream migration in Arctic lamprey ammocoetes in Kamchatka rivers. Ammocoetes of different age groups are shown to be constantly noted in the composition of the migrant part of a river community. The greatest intensity of downstream migration in ammocoetes of the age class 0+ is noted in the period of their primary dispersion in late July-early August. The ammocoetes of the age groups 1+ and older migrate from spring to late autumn, but their concentrations are not high. The significant similarity of such a biologic feature as downstream migration in ammocoetes and juvenile salmonids serves as an example of ecological analogy.     

Growth and intermediary metabolism of larval and metamorphosing stages of the landlocked sea lamprey,Petromyzon marinus L

Synopsis Seasonal changes in blood, liver and muscle substrate (glucose, glycogen and lipid) concentrations and enzyme (pyruvate kinase (PyK), fructose diphosphatase (FDPase), NADP-isocitrate dehydrogenase (ICDH), malic enzyme (ME) and the hexose monophosphate shunt dehydrogenases (HMSD)) activities were assessed in ammocoete and metamorphosing stages of a stream stock of the landlocked sea lamprey, Petromyzon marinus L. In all developmental stages studied, muscle rather than liver tissue served as the main site of carbohydrate and fat storage. Blood glucose and muscle lipid exhibited a positive relationship while liver HMSD and muscle ME activity, a negative relationship, with ammocoete weight. These responses were attributed to a proliferation of red fibers and adipocytes in the ammocoete muscle as the time of metamorphosis approched. Muscle lipid stores of ammocoetes in their last year of larval life increased dramatically during the fall and winter preceding metamorphosis. Changes in tissue enzyme activity of ammocoetes in their last year of larval life indicated that the liver was the site of amino acid incorporation into fat while muscle was the site of lipogenesis from glucose. During the non-trophic period of metamorphosis, stored material was catabolized to provide energy for protein synthesis.     

Lethal Temperatures in Ammocoetes of Four Species of Lampreys

Abstract 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.     

The systematics of British larval lampreys

Several taxonomic characters, including the number of trunk myomeres, proportional body measurements and patterns of external and internal pigmentation, have been investigated in populations of ammocoetes belonging to the three species of lampreys found in British rivers. Petromyzon marinus can be readily distinguished by the pigmentary pattern in the tail and on the oral hood, and by the much higher number of trunk myomeres. Although no character can be used to separate with certainty the larvae of Lampetra fluviatilis and Lampetra planeri , significant differences were found between the mean number of trunk myomeres in the two species. Moreover, the values for ammocoetes were virtually identical to those of the respective post-larval stages, at which phase in the life cycle the two Lampetra species are clearly distinguishable. The incidence of pigmentation on the tongue precursor was much higher in larval populations of L. fluviatilis than in those of L. planeri and there was also a difference in the rate of change in the relative length of the trunk and tail. Where comparisons can be made, the results in this paper are in agreement with those of most other European and North American workers. The data differ markedly, however, from that contained in the only other previous detailed systematic study on British larval lampreys, which was subsequently used as the basis for taxonomic keys.     

Lethal temperatures of ammocoetes of the Southern Hemisphere lamprey,Geotria australis Gray

Synopsis The resistance time of ammocoetes ofGeotria australis was related to the time of emergence from the substrate. The incipient lethal temperatures of animals acclimated at 5, 15 and 25° C were 27.3, 27.5 and 28.2° C respectively, the ultimate incipient lethal being 28.3° C. This value, which is similar to that of Northern Hemisphere lampreys such asLampetra planeri, almost certainly accounts for the restriction of this species to the southernmost rivers in Western Australia.     

Occurrence and Structure of Iron Inclusions in Adipocytes of Larval Lampreys

The occurrence and structure of adipocytes in the larvae of two lamprey species, Geotria australis and Petromyzon marinus, were examined by electron microscopy. Adipocytes from both species possessed large electron-dense inclusions which histochemical and energy dispersal X-ray analyses show as containing iron. The greatest concentration of inclusions in adipocytes was found in the nephric fold of G. australis. While some iron is present in the cytoplasmic matrix as ferritin, the majority is seen in large ammocoetes in membrane-bound dense aggregations of haemosiderin. The wide variety of inclusion types seen in smaller larvae may reflect on the method of formation of these inclusions within the cell. Because of the high level of iron loading in the larval lamprey nephric fold, this readily accessible tissue may provide a valuable model for studies of iron metabolism in vertebrates.     

Habitat preferences of Ukrainian brook lamprey Eudontomyzon mariae ammocoetes in the lowland rivers of Central Europe

The pattern of microhabitat preferences of Ukrainian brook lamprey Eudontomyzon mariae ammocoetes was examined in two rivers of central Poland: the Pilica River (the Vistula River basin) and the Grabia River (the Odra River basin). A comparison of abiotic factors of the rivers revealed differences in water speed and principal components: PC1 (determining gradient from decreasing medium sand to the increasing share of three fractions of gravel), PC2 (a gradient from the declining share of very coarse and coarse sand fractions to the growing content of fine sand) and PC3 (correlated with an increasing proportion of silt). The sites did not differ significantly in terms of water depth. Relative abundance and frequency of ammocoete occurrence in the Grabia River were higher than in the Pilica River. Only speed, PC1 and PC2 made a significant contribution to the prediction of larval occurrence. Eudontomyzon mariae larvae preferred substrata with a reduced amount of medium sand and increased content of gravel (PC1) as well as with a lower content of coarse sand and higher proportion of fine‐grained sand (PC2). The ammocoetes also preferred areas with a water speed of 0·2 m s^?1 but avoided speeds ≥0·6 m s^?1. The abundance of E. mariae was affected by water speed, as well as by all PCs. The mean ± s.e. optimal current speed was 0·265 ± 0·007 m s^?1, while abundance decreased with increasing amounts of gravel (PC1) and increased with increasing amounts of fine sand and silt in the bottom substratum (PC2 and PC3). Comparison of ammocoete microhabitat use in the Pilica and Grabia Rivers showed the lack of differences in distribution in the preferred values of current speed, PC1 and PC2.     

Larval growth in the river lamprey, Lampetra fluviatilis

A series of 987 ammocoetes from the rivers Towy, Teme, and Taw have been identified as mainly L. fluviatilis (L.) on the basis of oocyte counts on female ammocoetes. The length frequency distributions for this material differs from either L. planeri or P. marinus in showing only three modes in addition to the young of the year and the length distribution of the final mode coincides with the length range for 119 metamorphosing and macrophthalmia stages of L. fluviatilis that have been found at the same sites. These animals measured from 80–117 mm in length and weights varied from 0.76–2.28 g. Metamorphosis is believed to take place in late summer and early autumn when in the majority of cases, the ammocoetes are four and a half years old. The evidence that the non-parasitic L. planeri has a longer larval life than the closely related parasitic L. fluviatilis is thought to have some significance in relation to the evolution of the brook lamprey species.     

Structure and Development of the Notochord ‘Elastica Externa’ and Nearby Components of the Elastic Fibre System of Agnathans

Between 15 days and 3 months in age, the ‘elastica externa’ of the notochord sheath of larval lampreys develops from patches of moderately dense and amorphous material into a thick, continuous and electron-dense layer. In both lampreys and hagfish, this layer stains strongly with Verhoeff's elastic stain and aldehyde fuchsin and is penetrated by collagen fibrils on both its outer and inner boundaries. Peroxidase labelling using an antibody raised against human elastin specifically labels both the notochord ‘elastica externa’ and the elastic fibre system of lampreys. The diameters of the microfibrils (10–13 nm) of the oxytalan, elaunin and elastic fibres of lampreys and hagfish are the same as those of higher vertebrates. The connective tissue immediately dorsal and ventral to the notochord of lampreys contains mainly oxytalan fibres in very young ammocoetes, a combination of oxytalan, elaunin and elastic fibres in older ammocoetes, and predominantly elastic fibres in adult lampreys. While the region of the endomeninx at the base of the spinal cord contains almost exclusively oxytalan fibres in young ammocoetes, it also possesses numerous elastic fibres in adult lampreys. These findings indicate that, as in higher vertebrates, the elastic fibres of lampreys develop from oxytalan fibres via elaunin fibres.