The estuarine phase in the spawning run of the River lamprey Lampetra fluviatilis

The biology of the very early stages in the upstream migration of the River lamprey has been studied using samples taken from the cooling water intake screens of the Oldbury Power Station in the Severn Estuary. Examination of the numbers of lampreys caught at different times indicate that an increase in freshwater discharge is the predominant environmental factor responsible for initiating the movement from the sea into the estuary, although temperature may also be a contributory factor. The migrants could be separated on the basis of size into typical and praecox forms whose mean lengths during peak abundance were approximately 300 and 240 mm respectively, the corresponding weights being about 53 and 22 g respectively. The typical forms were occasionally found in the estuary as early as July and as late as April, with peak abundance generally being reached in November, whereas the praecox forms were present mainly between January and March. The ratio of typical to praecox forms over the four years of sampling was estimated as 3.3 : 1. In both size categories, the gonadosomic and hepatosomic ratio was greater in females than males. Evidence was also found in the typical forms for a correlation between high numbers and an increased proportion of males. Measurement of a number of different characters, including lengths, weights and condition factors, as well as gonadosomic, hepatosomic and gut ratios, suggest that, although the typical forms enter the estuary over a long period of time, the onset of the changes leading to sexual maturity are more synchronous. A small number of the later typical migrants, however, exhibited different characteristics to those of the majority of the animals comprising this size category. Measurements made on typical animals from Oldbury in November indicate that they can regulate their plasma ions in salinities as high as 70% of full strength sea water.     

Downstream migration and hematophagous feeding of newly metamorphosed sea lampreys (Petromyzon marinus Linnaeus, 1758)

The metamorphosis of sea lamprey (Petromyzon marinus Linnaeus, 1758) allows young postmetamorphic individuals to migrate to the sea and start the hematophagous feeding. However, the information about this phase is very limited, especially for European populations. Herein, we provide for the first time a comprehensive study on the phenology of downstream migration, the timing and location of first feeding and the prey species in the River Ulla and its estuary (NW Spain). Results show that downstream migration occurs between October and May with a peak in March. At least for a part of the postmetamorphic lampreys this migration stops for several months when they reach the estuary, where lampreys find shelter and abundant food, before moving to coastal waters. Hematophagous feeding in the estuary allows postmetamorphics to increase their total length and weight exponentially. Our results also suggest that part of the postmetamorphics (10–30%) start the hematophagous feeding in the river, with a special affinity for anadromous species, probably because of their larger size.     

Two records of sea lamprey from the north Aegean Sea

Two adult sea lampreys Petromyzon marinus , one female and one male, 742 and 645 mm L _T respectively, were caught in the north Aegean Sea, Greece (Vistonis bay and shore of Karvali). These two records are the first for the Aegean Sea and for the whole eastern Mediterranean.     

Combining limnological and palaeolimnological approaches in assessing degradation of Lake Pskov

Historical spawning grounds for sea lampreys (Petromyzon marinus L.) in most Portuguese river basins are becoming inaccessible due to the construction of impassable dams and/or weirs. Studies like the one described in this paper are particularly important in areas like the Vouga river basin, where there is a considerable fishing effort from both professional fishermen and poachers. In fact, for management and conservation purposes, it is important to clarify several aspects of the sea lamprey spawning run in this particular watershed. Therefore, a total of 30 radio tagged, migrating sea lampreys were released in the River Vouga and some of its main tributaries during 2004 and 2005. Results from the tracking sessions were used to determine the effect of poaching on the spawners’ population and the characteristics of the resting sites used during the upstream movement. The rivers’ stretches were also characterized according to the type of substrate present in the riverbed and flow type, in order to determine its aptitude to constitute appropriate spawning habitats for sea lampreys. We have identified in the upstream stretches of River Vouga, and in the tributary River Caima, characteristics that are particularly suitable for the construction of nests by the spawners. Presence of larvae provided evidence that spawners migrated into the River Vouga’s upper reaches. However, abundance and age class diversity appeared to be higher downstream of Sernada and Carvoeiro weirs, corroborating the telemetry data which suggested difficulty in passing these obstacles during low precipitation years. In the River Caima, migration was most predictable, which might be related to daily water releases from a small hydropower dam at dusk, that stimulated the lampreys to resume migration. Poaching has had a considerable negative effect on the success of the tagged lampreys’ migration: 76% of the animals released during 2005 were captured. Electronic supplementary material  Supplementary material is available for this article at and accessible for authorized user     

Parasitic Attachments by Overwintering Silver Lampreys, Ichthyomyzon unicuspis, and Chestnut Lampreys, Ichthyomyzon castaneus

We present evidence that at least some parasitic-phase silver lampreys, Ichthyomyzon unicuspis, and chestnut lampreys, I. castaneus, remain attached to host fish during the winter. Lake sturgeon, Acipenser fulvescens, harvested through the ice by spearfishers in the Lake Winnebago system in Wisconsin may bear silver lampreys or fresh lamprey wounds, and sturgeon with lamprey marks were significantly larger than sturgeon without them. Silver lampreys collected on paddlefish, Polyodon spathula, in the Wisconsin River in March were not significantly longer than silver lampreys collected previously in late October, but they were significantly heavier, an indication that they were feeding to at least some extent during the intervening period. Other large fish species, including northern pike, Esox lucius, and flathead catfish, Pylodictus olivaris, have been collected or observed during the winter with silver or chestnut lampreys attached. Although energy and nutrient intake by parasitic lampreys may be reduced during the winter, lampreys attached to hosts may also benefit from the hosts' mobility and ability to avoid potentially harmful situations.     

The age, growth and diet of a freshwater population of the flounder, Platichthys flesus (L.), in southern England

Otoliths from 640 flounders from the River Frome, a chalk river in southern England, were used for age and growth studies together with length-frequency data. Mean lengths at ages I–V were 89, 151, 225, 304 and 323 mm respectively; these are higher than have been reported for marine populations. All flounders caught were immature and, on reaching the sea, both sexes probably became sexually mature a year older than did the marine populations. Flounder diets in freshwater comprised largely aquatic insects, Mollusca and Crustacea but there were differences between large and small fish; seasonal changes in diet largely reflected prey availability. It is suggested that competition for food and space in estuaries between 0 group flounders have given rise to the migration into fresh water.     

Monthly changes in the swim bladder morphology of the female Japanese eel <Emphasis Type="Italic">Anguilla japonica</Emphasis> in the coastal waters of Mikawa Bay,Japan

In the coastal area of Mikawa Bay, central Japan, specimens of the female Japanese eel Anguilla japonica could be divided into two groups according to the degree of swim bladder development. In one case, they were undeveloped, and in the other, they were highly developed with large rete mirabile, thick submucosa, and a well-developed gas gland. The morphology of the swim bladder in the latter group was comparable with that in the artificially fully maturated eel. The specimens with an undeveloped swim bladder were caught during all months, although their number was small. The specimens with a highly developed swim bladder were most abundant in November and December. During these months, catch of the specimens also increased sharply, by more than 10 fold compared to that in other months. These observations indicate that most of the eel appearing in coastal Mikawa Bay from October to January have a highly developed swim bladder adapted for a deep-sea environment. It was also conjectured that these specimens most likely migrated from rivers feeding into Mikawa Bay, toward spawning grounds in the open sea, and that this occurred after development of their swim bladders was completed. Actually, the specimens caught in the upstream of the Toyo River feeding into Mikawa Bay from late August to early October already had highly developed swim bladders.     

Residence time of the sea louse, Lepeophtheirus salmonis K., on Atlantic salmon, Salmo salar L., after immersion in fresh water

Returning adult salmon caught at the mouth of the River Dee, Aberdeenshire, were transferred to tanks in the laboratory. For fish placed in fresh water, sea lice remained attached for up to 6 days, though most lice were lost in the first 48 hours. Few lice were lost from salmon maintained in sea water. The experiments were conducted in water within a temperature range of 12·8 to 16° C, equivalent to summer river temperatures in the Aberdeenshire Dee.     

Quantitative data on morphology and organ weights during the protracted spawning-run period of the Southern Hemisphere lamprey Geotria australis

Data are presented for a wide variety of different measurements and observations made on representatives of the lamprey Geotria australis caught during the first four months after they had left the sea in seven successive years. Comparisons have been made with the trends shown by similar data obtained from animals subsequently held in the laboratory for a number of months to provide information on the subsequent pattern of changes and the duration of the spawning run. In comparison with anadromous holarctic species, the gonads at the beginning of the upstream migration in July were very small. The eggs, which did not yet contain yolk platelets, measured only 190 μm in diameter and took until October of the following year to reach 1120 μm, which is comparable to the size of the mature eggs of other lampreys. This indicates that the spawning run of G. australis lasts for the exceptionally long period of 16 months, which is consistent with the time of appearance of young larvae. At the commencement of the spawning run, the mean lengths and weights of G. australis were approximately 655 mm and 250 g. Hepatosomic (c. 0·8%) and heart ratios (c. 0·18%) were significantly lower than those of other species. The relatively long length of the trunk, which was associated with a very high mean myomere number (78·8), helped to compensate for a small body depth and permitted the production of a large number of eggs (mean fecundity 57,943). The intestine underwent rapid atrophy immediately after the animal entered fresh water, even though the gonads were not developing rapidly at this time. Migratory movements in the river were most marked on nights when water levels were rising, the temperature lay between 12 and 14.5°C, rain was falling and extensive cloud cover or the dark phase of the moon was present.     

Migration and spawning energetics of the anadromous sea lamprey,Petromyzon marinus

Synopsis Energy expended in migration and reproduction was determined from measurements of caloric concentration and body and gonodal weight for nontrophic sea lampreys collected from different sites along the St. John River, New Brunswick. The estimated cost of locomotion in swimming the 140 km which separates the estuary from the spawning redds was 300 and 260 kcal for males and females respectively. Acutal distance which lampreys swam as well as mean swimming speed were estimated from a linear regression equation relating energy expenditure for locomotion and body weight. Energy expenditure for breeding was considerably greater than that catabolized throughout the upstream migration.     

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.     

Growth and abundance of O-group herrings, Clupea harengus L., in the Severn Estuary

Collections made from the cooling water intake screens of Power Stations in the Severn Estuary and the Bristol Channel have been used to investigate the biology of O-group herrings in this region. The abundance of herrings at Oldbury, the principal sampling site, was low in most years and in five successive seasons between July 1972 and December 1976, large numbers were caught only between the summer of 1975 and the spring of 1976. The herrings were first observed in July, when many had still not completed metamorphosis, and reached peak numbers in September and October during which period they were clearly growing. Numbers declined in December before rising dramatically in January at which time the length-frequency curves displayed a pronounced bimodality. On the basis of data from other parts of the Bristol Channel and Severn Estuary, it is suggested that this bimodality is due to the influx of some animals from other regions where the growth rate was greater. Although movement is apparently taking place at this time and the numbers decline markedly in subsequent months, the last remnants of the population do not leave the estuary until early May. Post-pelvic scute (K₂) and vertebral counts (VS) of 13.82 and 55.24 respectively, indicate that the Severn Estuary herrings are the product of a spring spawning stock, a view entirely consistent with length and field data.     

Migration, growth and survival of wild and hatchery-reared anadromous Arctic charr (Salvelinus alpinus) in Finnmark, Northern Norway

Two groups of anadromous Arctic charr ( Salvelinus alpinus ) (size 200–350 mm) reared in heated water (6–12° C) under simulated natural photoperiod were individually tagged and released in spring 1988. The fish were released at two sites, in the estuary of the River Halselva and in the fjord, 2 km from the river mouth. Growth, timing of migration and survival of these hatchery-reared fish was compared to that of wild anadromous charr of the same size over a 4-year period. The hatchery-reared charr had poorer growth than the wild fish during their first year in sea water. They also resided longer in the sea and had a slightly lower survival than wild fish. During the second year, hatchery-reared charr displayed good growth, and after the third sea-season the fish were ready for slaughter at a size of approximately 800g. The results suggest that the successful development of Arctic charr ranching will be dependent upon production and release strategies that lead to improved migratory and feeding behaviour of the fish during their first season at sea.     

Initiation of flight in the unrestrained fly, Drosophila melanogaster

Neocalceostomoides brisbanensis sp. nov. from the gill arches, gill rakers and buccal lining of the blue catfish, Arius graeffei , is described. It is distinguished from the type species Neocalceostomoides arii (Unnithan, 1964) by the presence of a convoluted vas deferens with a blind-ending diverticulum; two lobes inside the vagina, each with ornamentation comprising rows of conical studs; two seminal receptacles and a post-testicular connection between the gut caeca. There is a closer resemblance to Neocalceostomoides spinivaginalis Lim, 1995, which also has vaginal lobes with ornamentations, but in N. spinivaginalis these ornamentations are elongated and spine-like and the penis tube and 'gubernaculum' are significantly longer. Neocalceostomoides brisbanensis was found on A. graeffei caught in Moreton Bay (sea water), Queensland, but not on catfish caught in the Brisbane River (fresh water). Some comments are made on the evolution and relationships of calceostomatines.     

Spawning Periodicity, Spawning Migration, and Size at Maturity of Green Sturgeon, Acipenser medirostris, in the Rogue River, Oregon

The Rogue River, Oregon represents one of three important spawning systems for green sturgeon, Acipenser medirostris, in North America. In this paper we describe the spawning migration, spawning periodicity, and size at maturity for green sturgeon caught in the Rogue River during 2000–2004. Green sturgeon were caught by gill net or angling; 103 individuals were tagged with radio or sonic transmitters (externally or internally). Green sturgeon caught by gill net and angling ranged from 145 cm to 225 cm total length. Histological and visual examinations of gonad tissues indicated that most green sturgeon were spawning or post-spawning adults that entered the Rogue River to spawn. Ripe individuals were caught when water temperature was 10–18°C. Specimens carrying transmitters migrated 17–105 km up river; reaches consisting of likely spawning sites were identified based on sturgeon migratory behavior. Most green sturgeon remained in the Rogue River until late fall or early winter when flows increased, after which they returned to the ocean. Eight green sturgeon (males and females) returned to the Rogue River 2–4 years after leaving, entering the river during March, April, and May when water temperatures ranged from 9°C to 16°C. None of the 103-tagged individuals entered the Rogue River during successive years. There appear to be few known natural threats to adult green sturgeon in the Rogue River. However, our data suggest that a high percentage of adults that spawn in the Rogue River (particularly males) were susceptible to harvest by commercial, Tribal, and sport fisheries after leaving the system because they were not adequately protected by maximum size limits during the period of this study. The implications of maximum size limits (or lack of size limits) to green sturgeon are discussed, and recent actions taken by Oregon and Washington Fish and Wildlife Commissions to manage green sturgeon more conservatively are presented.     

Captures of Pacific halibut <Emphasis Type="Italic">Hippoglossus stenolepis</Emphasis> (Pleuronectidae) in Anadyr estuary of the Bering Sea

Pacific halibut Hippoglossus stenolepis is registered in the Anadyr estuary (Bering Sea basin) for the first time: 20 specimens, 18.5–160.5 cm in length, were caught by trawl and longline within the sea portion of the Anadyr River estuary in August 2010 and September 2015 in highly desalted (23.5‰ on average) and heated (6.5°С) water at a depth of 14–30 meters. Halibut is suggested to form feeding groups within the Anadyr Estuary. An opportunity for organized fishing in this region is discussed.     

The use of PIT telemetry to study movements of ammocoetes and metamorphosing sea lampreys in river beds

Passive integrated transponder (PIT) tags were surgically implanted in 118 sea lamprey Petromyzon marinus ammocoetes which were left to recover in the laboratory for 2 months. During this period 55 individuals started to metamorphose. In the late summer of 2002 the tagged animals were released in a small tributary of the River Mondego, Portugal, and were regularly monitored for a period of 2 months using a portable PIT tag reader. The distribution of the released animals changed from an initial uniform pattern to a random distribution, and then to an aggregated pattern. At the end of the first week 60% of the tagged sea lampreys had already left the study area, indicating their dynamic behaviour. Ammocoetes were more active than metamorphosing sea lampreys, and downstream movements were more frequent when compared to the upstream ones, which were usually a short distance. In order to determine the influence of the dark‐light cycle in the diel activity rhythms, 10 tagged sea lamprey ammocoetes were released in a tank (2000 l capacity) and their position monitored twice a day, for a period of 1 month. Ammocoetes locomotor activity appeared to be conditioned by circadian rhythms, and they were particularly active during darkness.     

The estuarine biology of the River lamprey, Lampetra fluviatilis, in the Firth of Forth, Scotland, with particular reference to size composition and feeding

Samples collected regularly during 1979, 1980 and 1981 from the intake screens of power stations in the estuary of the River Forth produced data on the estuarine phase in the life cycle of the River lamprey, Lampetra fluviatilis. Recently metamorphosed animals were common during the spring while sexually maturing adults were abundant in the late summer and autumn. These were assumed to be lampreys at the end of their downstream and start of their upstream migrations respectively. The respective sizes of the presumed downstream and upstream migrants were 69–135 mm (0-2-2-8 g) and 200–361 mm (7-0-93-2 g). Smaller numbers of animals of intermediate size were collected during the summer and late autumn. Males were usually the predominant sex with an average of 56–5% of the population in 1980–1981. In all months, the mean weight and with one exception also the mean length, was greater for females than for males. The intestine frequently contained fish remains, especially muscle, bone and scales of clupeids and thus the River lamprey seems to feed mainly on teleosts in this estuary. An analysis of the size of scales in the intestines of lampreys of various body lengths indicates that there is a relationship between the size of host and predator. Comparisons with other studies of Lampetra fluviatilis emphasize the variability that exists in aspects of the biology of this species within and among populations.     

Relationship of density to growth and metamorphosis of caged larval sea lampreys, Petromyzon marinus Linnaeus, in Michigan streams

Larval sea lampreys, Petromyzon marinus , of the 1976 year class were studied between May 1977 and October 1981 in five Michigan streams to determine the relationship of density to growth and metamorphosis. Two cages were placed in each stream; one cage contained 25 larvae (low density group) and the other 75 larvae (high density group). Changes in body length, as an indicator of growth, were monitored in all streams from age I to V. Mean lengths ranged from 25 to 55 mm at the beginning of the study and from 102 to 158 mm at the end. Some ammocoetes attained lengths greater than 160 mm. Growth was related mainly to density; crowding affected growth from age I to metamorphosis. Mean increases of total length ranged from 90 to 128 mm among low-density groups and from 54 to 97 mm among high-density groups. Growth was typically greater in the cage with fewer lampreys in each stream. Most growth occurred from May to October when stream temperatures were highest. In two streams in which cages were not vandalized, 96% and 92% of the lampreys in the low-density groups and 68% and 52% in the high-density groups survived to age V. Metamorphosis occurred at age V in low-density groups. Five lampreys (2.4%; range, 133–145 mm long) metamorphosed among the 207 that survived until completion of the study.     

Distribution, migrations and growth of tagged Drawa salmon (Salmo salar L.)

A total of 4450 tagged two and three years old salmon smolt were released into the River Drawa. Tagged salmon was caught mainly in central Baltic. Downstream migrating smolt were caught in lower Oder River till mid-May, and in the Szczecin Firth till the first decade of June. After reaching the sea, the tagged salmon migrated northeastward. They remained most of all in the central Baltic and were mainly caught near Gotland. In autumn of the third year after the release salmon were present on the spawning grounds. The fish attained an average of 58.2 cm and 1892g after the first year of sea life, 78.0 cm and 5329g after the second year, and 98.5cm and 9100g after the third year. Most of the tagged Drawa salmon were caught by Danish (44.7%) and Swedish (25.9%) fishermen.