Seasonal variations of opisthaptoral hard parts of Gyrodactylus salaris Malmberg, 1957 (Monogenea: Gyrodactylidae) on parr of Atlantic salmon Salmo salar L. in the River Batnfjordselva,Norway

Seasonal variations in size and shape of the marginal hooks, the anchors and the ventral bar of the opisthaptor of Gyrodactylus salaris Malmberg, 1957 were studied. The G. salaris specimens were collected from parr of Atlantic salmon Salmo salar L. in the River Batnfjordselva, north-western Norway. Samples were taken at roughly monthly intervals during a two-year period. The marginal hooks, the anchors and the ventral bar showed considerable seasonal variation in size, but varied only slightly in shape. The variation in 12 of the 14 characters measured showed a significant regression to the variation in the water temperature. The total length of the marginal hooks of G. salaris can be considerably longer than the previously reported maximum of 40 m for the species.     

Gyrodactylus gvozdevi n. sp. (Gyrodactylidae: Monogenea) from Noemacheilus dorsalis (Kessler) in Kazakhstan

Gyrodactylus gvozdevi n. sp. (Gyrodactylidae: Monogenea) is described from the skin of the freshwater fish Noemacheilus dorsalis (Kessler) (Cobitidae: Cypriniformes) from Kazakhstan. This species is most closely related to G. pseudonemachili Ergens & Bykhovsky, 1967 in the shape and size of the anchors and both the ventral and dorsal bars, but can be distinguished from it by the shape and size of the hookproper of the marginal hooks.     

Gyrodactylus sommervillae n. sp. (Monogenea) from Abramis brama (L.) and Rutilus rutilus (L.) (Cyprinidae) in Oxfordshire,UK

Gyrodactylus sommervillae n. sp. (Monogenea) is described from the skin, fins and gills of Abramis brama (L.) and Rutilus rutilus (L.) from Blenheim Palace Lake, Oxfordshire, UK. G. sommervillae n. sp. closely resembles G. aphyae Malmberg, 1957, G. kearni Ergens, 1990 and G. lamberti Ergens, 1990 in the approximate shape of the marginal hook sickle and the anchors, but can be separated on the precise shape of the marginal hooks and the ventral bar.     

Variations of opisthaptoral hard parts of Gyrodactylus salaris Malmberg, 1957 (Monogenea: Gyrodactylidae) on rainbow trout Oncorhynchus mykiss (Walbaum, 1792) in a fish farm,with comments on the spreading of the parasite in south-eastern Norway

Studies were carried out on Gyrodactylus salaris Malmberg, 1957 on rainbow trout Oncorhynchus mykiss (Walbaum, 1792) from a fish farm in Lake Tyrifjorden, south-eastern Norway. The anchors were larger, and the shape of the anchors and the ventral bar differed slightly, as compared with the same parts of G. salaris on parr of Atlantic salmon Salmo salar L. in northern and north-western Norwegian rivers. At different water temperatures (0.8°C, 10.0°C, 18.0°C), the opisthaptoral hard parts of G. salaris on rainbow trout showed considerable variation in size, but varied only slightly in shape. It was found that the total length of the anchors of G. salaris on rainbow trout may considerably exceed the previously reported maximum of 80 m for the species. The spread of G. salaris to south-eastern Norway is described and discussed.     

A description of a new species Gyrodactylus moldovicus sp. n. (Monogenea: Gyrodactylidae) from the European mudminnow Umbra krameri Walbaum, 1792 from the lower Dnester basin

Gyrodactylus moldovicus sp. n. found on gills, body and in nasal cavities of the European mudminnow (Umbra krameri) differs from G. slovacicus Ergens, 1963 also living on the this host by bigger size of the body, anchors and marginal hooks; from G. cylindriformes Mueller et Van Cleave, 1932 living on the American mudminnow Umbra limi--by bigger size of the body; from G. limi Wood et Mizelle, 1957 also from U. limi--by the form of ventral and dorsal bars and form of marginal hooks. It differs from other freshwater gyrodactylids by special type of marginal hooks which have a hook-like end of the blade. Gyrodactylus moldovicus, G. slovacicus and G. limi have marginal hooks of quite different morphological types. By the morphology of anchors, ventral and sometimes dorsal bars and also morphology of cirrus, G. moldovicus is most related to three species from Cyprininae: G. stankovichi Ergens, 1970, G. longoacuminatus Zitnan, 1964 f. typica and G. shulmani Ling, 1962.     

Variations of opisthaptoral hard parts of Gyrodactylus salaris Malmberg, 1957 (Monogenea: Gyrodactylidae) on parr of Atlantic Salmon Salmo salar L. in laboratory experiments

On parr of Atlantic salmon Salmo salar L. in laboratory experiments at different water temperatures, opisthaptoral hard parts of Gyrodactylus salaris Malmberg, 1957 differed in size. Their shape, on the other hand, varied only slightly. The opisthaptoral hard parts were largest at the lowest water temperatures and decreased in size with increasing water temperatures (1.5°C to 20.0°C). At both 18.0°C and 20.0°C the opisthaptoral hard parts of G. salaris were smaller than has been found under natural conditions. In the experiments, the mean size of the opisthaptor in the G. salaris micropopulation at each water temperature gradually increased or decreased compared to the mean size at the start of the experiments. At the end of the experiments the mean size of the opisthaptoral hard parts in the G. salaris micropopulations showed a significant regression to the different water temperatures.     

Farmed Atlantic salmon Salmo salar L. parr may reduce early survival of wild fish

The study examined the density‐mediated effects on growth, survival and dispersal of wild and farmed Atlantic salmon Salmo salar offspring in the period immediately following emergence, using a substitutive design. In small confined stream channels, wild parr coexisting with farmed parr had a significantly poorer survival, than wild parr alone. Density did not affect this relationship. In larger unconfined stream channels, wild parr coexisting with farmed parr entered a downstream trap in higher numbers than wild parr in allopatry. The results suggests that during the earliest life stages, farmed S. salar can outcompete wild S. salar, resulting in a reduced survival of wild S. salar.     

The description of Gyrodactylus mulli sp. n. (Monogenea: Gyrodactylidae) from the Black Sea blunt-snouted mullet Mullus barbatus ponticus

A new species Gyrodactylus mulli sp. n. is described from the thorax fins of blunt-snouted mullet Mullus barbatus ponticus by the collections of B. E. Bychowsky made in 1947 near Karadag on the Black Sea. Gyrodactylus mulli sp. n. differs from G. alviga Dmitrieva et Gerasev, 2000 (described from blunt-snouted mullet too) in having another morphotype of the marginal hooks. The new species differs from G. proterorhini Ergens, 1967, which has the identical type of the marginal hooks, in having longer membrane of the ventral connective bar, longer point of the anchors, shorter marginal hooks, and lesser size of the cirrus.     

On the ontogeny of the haptor and the evolution of the Monogenea

Data on the ontogeny of the posterior haptor of monogeneans were obtained from more than 150 publications and summarised. These data were plotted into diagrams showing evolutionary capacity levels based on the theory of a progressive evolution of marginal hooks, anchors and other attachment components of the posterior haptor in the Monogenea (Malmberg, 1986). 5 + 5 unhinged marginal hooks are assumed to be the most primitive monogenean haptoral condition. Thus the diagrams were founded on a 5 + 5 unhinged marginal hook evolutionary capacity level, and the evolutionary capacity levels of anchors and other haptoral attachement components were arranged according to haptoral ontogenetical sequences. In the final plotting diagram data on hosts, type of spermatozoa, oncomiracidial ciliation, sensilla pattern and protonephridial systems were also included. In this way a number of correlations were revealed. Thus, for example, the number of 5 + 5 marginal hooks correlates with the most primitive monogenean type of spermatozoon and with few sensillae, many ciliated cells and a simple protonephridial system in the oncomiracidium. On the basis of the reviewed data it is concluded that the ancient monogeneans with 5 + 5 unhinged marginal hooks were divided into two main lines, one retaining unhinged marginal hooks and the other evolving hinged marginal hooks. Both main lines have recent representatives at different marginal hook evolutionary capacity levels, i.e. monogeneans retaining a haptor with only marginal hooks. For the main line with hinged marginal hooks the name Articulon-choinea n. subclass is proposed. Members with 8 + 8 hinged marginal hooks only are here called Proanchorea n. superord. Monogeneans with unhinged marginal hooks only are here called Ananchorea n. superord. and three new families are erected for its recent members: Anonchohapteridae n. fam., Acolpentronidae n. fam. and Anacanthoridae n. fam. (with 7 + 7, 8 + 8 and 9 + 9 unhinged marginal hooks, respectively). Except for the families of Articulonchoinea (e.g. Acanthocotylidae, Gyrodactylidae, Tetraonchoididae) Bychowsky's (1957) division of the Monogenea into the Oligonchoinea and Polyonchoinea fits the proposed scheme, i.e. monogeneans with unhinged marginal hooks form one old group, the Oligonchoinea, which have 5 + 5 unhinged marginal hooks, and the other group form the Polyonchoinea, which (with the exception of the Hexabothriidae) has a greater number (7 + 7, 8 + 8 or 9 + 9) of unhinged marginal hooks. It is proposed that both these names, Oligonchoinea (sensu mihi) and Polyonchoinea (sensu mihi), will be retained on one side and Articulonchoinea placed on the other side, which reflects the early monogenean evolution. Except for the members of Ananchorea [Polyonchoinea], all members of the Oligonchoinea and Polyonchoinea have anchors, which imply that they are further evolved, i.e. have passed the 5 + 5 marginal hook evolutionary capacity level (Malmberg, 1986). There are two main types of anchors in the Monogenea: haptoral anchors, with anlages appearing in the haptor, and peduncular anchors, with anlages in the peduncle. There are two types of haptoral anchors: peripheral haptoral anchors, ontogenetically the oldest, and central haptoral anchors. Peduncular anchors, in turn, are ontogenetically younger than peripheral haptoral anchors. There may be two pairs of peduncular anchors: medial peduncular anchors, ontogentically the oldest, and lateral peduncular anchors. Only peduncular (not haptoral) anchors have anchor bars. Monogeneans with haptoral anchors are here called Mediohaptanchorea n. superord. and Laterohaptanchorea n. superord. or haptanchoreans. All oligonchoineans and the oldest polyonchoineans are haptanchoreans. Certain members of Calceostomatidae [Polyonchoinea] are the only monogeneans with both (peripheral) haptoral and peduncular anchors (one pair). These monogeneans are here called Mixanchorea n. superord. Polyonchoineans with peduncular anchors and unhinged marginal hooks are here called the Pedunculanchorea n. superord. The most primitive pedunculanchoreans have only one pair of peduncular anchors with an anchor bar, while the most advanced have both medial and lateral peduncular anchors; each pair having an anchor bar. Certain families of the Articulonchoinea, the Anchorea n. superord., also have peduncular anchors (parallel evolution): only one family, the Sundanonchidae n. fam., has both medial and lateral peduncular anchors, each anchor pair with an anchor bar. Evolutionary lines from different monogenean evolutionary capacity levels are discussed and a new system of classification for the Monogenea is proposed.In agreeing to publish this article, I recognise that its contents are controversial and contrary to generally accepted views on monogenean systematics and evolution. I have anticipated a reaction to the article by inviting senior workers in the field to comment upon it: their views will be reported in a future issue of this journal. EditorIn agreeing to publish this article, I recognise that its contents are controversial and contrary to generally accepted views on monogenean systematics and evolution. I have anticipated a reaction to the article by inviting senior workers in the field to comment upon it: their views will be reported in a future issue of this journal. Editor     

Impact of precocious male parr on the effective size of a wild population of Atlantic salmon

1. There is growing evidence that sexually mature but morphologically juvenile males of Atlantic salmon (precocious or mature male parr) actively participate in reproduction and, therefore, in the genetic composition of the populations of this species. The impact of mature male parr on the effective population size (N_e) of such populations has been previously studied under experimental settings, but no studies have been performed directly on natural populations. 2. Continuous monitoring and sampling of all sea returns is possible in the Lérez River (northwest of Spain). From demographic data on variances of reproductive success and genetic data from six microsatellite marker loci we carried out parentage assignment and assessed the impact of male parr on demographic and genetic estimates of N_e in two consecutive years. 3. Our results reveal that: (i) approximately 60% of the total sire paternity is attributable to mature parr; (ii) mature parr decrease the variance of reproductive success of males by a threefold factor and increase the effective population size of males by a 10‐fold factor; (iii) however, they do not substantially affect the variance of reproductive success and the effective size of females; (iv) mature parr increase two‐to threefold the overall effective size of the population but the ratio N_e/N, where N is the population size including or not mature parr in each case, is not affected.     

A special technique for studying haptoral sclerites of monogeneans

The marginal hooks and anchors have been digested from the haptors of the monogeneans Gyrodactylus salaris and Discocotyle sagittata. These structures then can be measured and drawn more accurately than those surrounded by haptoral tissue. The technique also facilitates the study of isolated hooks with SEM. The results of studies using this digestion technique are presented.     

An SEM study of the haptoral sclerites of the genus Gyrodactylus Nordmann, 1832 (Monogenea) following extraction by digestion and sonication techniques

Techniques for the preparation of haptoral sclerites of Gyrodactylus species for scanning electron microscopy are described. Enzymatic digestion using pepsin allows fresh, frozen and alcohol-fixed material to be examined, but some sclerites, such as the dorsal and ventral bars, are lost. Sonication of fresh and frozen material retained these accessory bars, including the ventral bar membrane, the guard or sickle filament loop on the marginal hooks and even on some occasions ligaments associated with the sclerites. The sclerites of Gyrodactylus spp. from Gasterosteus aculeatus (L.) (three-spined stickleback), Oncorhynchus mykiss (Walbaum) (rainbow trout) and Salvelinus alpinus (L.) (charr) are described from SEM observations following the use of these preparation techniques, and the articulation between the hamuli and bars is commented upon.     

Metabolic recovery in Atlantic salmon fry and parr following forced activity

Atlantic salmon Salmo salar fry and parr were subjected to 5 min of forced activity and the subsequent changes in oxygen consumption and ammonia excretion rates were evaluated over a 24 h period. In a second experiment, individual Atlantic salmon fry and parr were freeze‐clamped in liquid nitrogen, before, immediately following a 5 min activity period, or after periods of recovery up to 2 h. Samples were analysed for whole body phosphocreatine (PCr), ATP and lactate. Five minutes of forced activity resulted in significant increases in both oxygen consumption and ammonia excretion rates. Changes in the oxygen consumption rates were greater in the parr compared with the fry. In contrast, the post‐exercise ammonia excretion rates were nearly twice as high for the fry compared with the parr. Exercise also caused a marked decrease in PCr levels (c. 47 and 65% in fry and parr, respectively), no change in ATP levels and a significant increase in lactate levels in Atlantic salmon fry and parr. Recovery of PCr occurred quickly (between 15 and 30 min) in fry and parr. Although the post‐activity levels of lactate were lower in fry (c. 3 μmol g^?1) compared with parr (c. 14 μmol g^?1), lactate levels returned to control levels within 60 min in fry, but it took >2 h for this metabolite to recover in parr. Compared with parr, these findings show that Atlantic salmon fry possess a reduced anaerobic capacity, and these results are consistent with the theoretical and experimental evidence that smaller fish support burst swimming through aerobic processes.     

<Emphasis Type="Italic">Gyrodactylus thlapi</Emphasis>n. sp. (Monogenea) from <Emphasis Type="Italic">Pseudocrenilabrus philander philander</Emphasis> (Weber) (Cichlidae) in the Okavango Delta,Botswana

A new species of Gyrodactylus von Nordmann, 1832 and the first monogenean reported from Botswana is described from the cichlid Pseudocrenilabrus philander philander,bringing the number of gyrodactylids described from the African Continent to 18. Gyrodactylus thlapi n. sp. can be readily discriminated from the other described species almost exclusively by the shape of its hamuli, which have short roots and large, elongate ventral bar attachment points with the dorsal bar attachment point, demarcating the junction between the hamulus shaft and the root, positioned at the anterior terminus of the attachment plane. The marginal hooks of G. thlapi n. sp., which most closely resemble those of G. groschafti Ergens, 1973, are compared and discussed.     

Factors affecting aggressive behaviour of spawning migratory males towards mature male parr in masu salmon Oncorhynchus masou

This study examined whether dominant migratory males (adopting fighter tactics) of the masu salmon Oncorhynchus masou would more aggressively attack large mature male parr (adopting sneaker tactics) as large mature male parr are expected to have the potential to cause a greater decrease in fertilization success. The frequency of aggressive behaviour was not related to the body size of males, and it increased with the frequency of interactions with mature male parr. The fertilization success of mature male parr was much lower than migratory males, and no relationship was observed between fertilization success and aggressive behaviour. The low fertilization success of mature male parr, despite infrequent aggressive behaviour by migratory males, indicates that there might be little benefit for migratory males to attack mature male parr more aggressively according to their body size.     

Daily endocrine profiles in parr and smolt Atlantic salmon

To elucidate possible mechanisms behind the endocrine control of parr–smolt transformation, the daily plasma profiles in thyroid hormones (TH; free thyroxine (FT₄), total thyroxine (TT₄), and total 3,5,3′-triiodothyronine (TT₃)), growth hormone (GH) and cortisol were studied in Atlantic salmon parr and smolts under simulated-natural winter (8 L:16D) and spring (16.5 L:7.5D) photoperiods, respectively. Overall, TT₄, TT₃ and GH levels were higher in smolts than in parr, whereas FT₄ levels fluctuated within the same range in parr and smolts. Significant diurnal changes in plasma TH were present in parr. Both FT₄ and TT₄ levels increased during the photophase and decreased during the scotophase, while TT₃ levels followed an inverse pattern. Growth hormone showed no significant changes in parr. Changes in FT₄, TT₄, GH, and cortisol, but not TT₃, levels, were observed in smolts with peak levels during both the photophase and scotophase for FT₄, TT₄ and GH. Plasma cortisol was not assayed in parr but in smolts the peaks were associated with dusk and dawn. In addition to the general increases in TH, GH and cortisol, the distinct endocrine differences in nighttime levels between parr in the winter and smolts in the spring suggest different interactions between TH, GH, cortisol and melatonin at these different time points. These spring scotophase endocrine profiles may represent synergistic hormone interactions that promote smolt development, similar to the synergistic endocrine interactions shown to accelerate anuran metamorphosis. The variations in these diurnal rhythms between parr and smolts may represent part of the endocrine mechanism for the translation of seasonal information during salmon smoltification.     

Gyrodactylus quadratidigitus n. sp. (Monogenea: Gyrodactylidae), a parasite of the leopard-spotted goby Thorogobius ephippiatus (Lowe) from the south-western coast of the UK

Gyrodactylus quadratidigitus n. sp. (Monogenea, Gyrodactylidae) is described from the gills, fins and skin of Thorogobius ephippiatus (Lowe) (leopard-spotted goby) from Portland Castle Bay, Dorset, UK. G. quadratidigitus n. sp. most closely resembles the species ofGyrodactyluspreviously described by Geets from Pomatoschistus microps(Krøyer) in the approximate shape and size of the attachment hooks but can be readily distinguished from other species of the genus by the distinctive square shape of the toe region of the marginal hook sickle, the anteriorly positioned cirrus bulb and the unusually short intestinal crura which extend only as far as the level of the testes.     

Bucephaline digeneans (Bucephalidae) in <Emphasis Type="Italic">Sphyraena putnamae</Emphasis> Jordan &; Seale (Sphyraenidae) from the lagoon off New Caledonia

Lethrinitrema gibbus n. g., n. sp. and L. dossenus n. sp. are described from the fish Lethrinus rubrioperculatus Sato collected off New Caledonia, South Pacific. Members of Lethrinitrema n. g. (Ancyrocephalidae) are characterised by having two pyriform haptoral reservoirs and ventral anchors with lateral grooves. The elongate tubular distal end of each reservoir bifurcates, draining into a superficial lateral groove on each side of the ventral anchors. The haptoral reservoirs are postulated to store secretory products which assist in attachment to the host. Lethrinitrema spp. also possess tandem gonads, a male copulatory organ without an accessory piece or with thinly sclerotised accessory piece, and a dextrolateral, non-sclerotised vaginal bulb. The two new species have small, poorly demarcated haptors with small haptoral armament and a crown-like piece on the tip of the inner root of the ventral anchors. They differ from each other in the shape and size of the ventral bar and male copulatory organ (40–45 μm in length in L. gibbus vs 24–30 μm in L. dossenus). Three other species, previously included in Haliotrema Johnston & Tiegs, 1922, are transferred to Lethrinitrema, i.e. L. chrysostomi (Young, 1968) n. comb., L. fleti (Young, 1968) n. comb. (both briefly redescribed from paratypes) and L. lethrini (Yamaguti, 1937) n. comb. All species of Lethrinitrema parasitise Lethrinus spp. (Lethrinidae), and there is evidence for the existence of further Lethrinitrema spp. on Lethrinus spp. in the Indo-Pacific region.     

Changes in smolt traits of Atlantic salmon (Salmo salar Linnaeus, 1758) and linkages to parr density and water temperature

Smolt traits (length, age) and timing of smolt migration of wild Atlantic salmon, Salmo salar L., were investigated in the Simojoki River, northern Baltic Sea. The aim was to determine whether they responded to changes in parr length, parr density and temperature from 2000 to 2014. Annual electrofishing surveys and smolt numbers determined parr densities by springtime trapping in the river mouth. During the smolt trapping period captured parr and smolts were aged from scales. Water temperature was measured daily. Mean length decreased from 137 mm (TL) to 129 mm among 2‐year‐old smolts, and from 150 mm to 139 mm among 3‐year‐olds. Median date of the smolt migration was 10 days earlier, from early June to late May during the study period, linked to the rise in air temperature in May at the nearby Kemi‐Tornio airport. However, the median day temperature and the mean daily water temperatures during the second (Q₂) and third (Q₃) migration quartiles did not change. This implied that migration began when a suitable water temperature was reached, independent of the date.     

Mid-winter activity and movement of Atlantic salmon parr during ice formation events in a Norwegian regulated river

A telemetry study in a Norwegian regulated river was conducted through a 12-day period in mid-winter 2003. The objective was to study activity (defined as number of movement per hour) and movement (defined as distance moved per hour) during different ice formation events. Twenty-four Atlantic salmon (Salmo salar L.) parr were radio tagged and continuously monitored by both manually tracking (N = 24) and by fixed recording stations (N = 15). Detailed data on climate, flow and ice formation and its spatial distribution were collected and used in the analyses. Fish activity was not found to be affected by their size (L _F). There was a significant difference in activity between diel periods with highest activity during dusk (5–6 p.m.). Between high and low flow (mean ± SD, 21.1 m³ s⁻¹ ± 1.7 SD and 11.1 m³ s⁻¹ ± 1.7 SD, respectively) no significant difference in activity was found. During the experiment extensive anchor ice growth occurred mainly in the riffle part with thickness up to 50 cm. Juveniles tend to avoid riffle section during anchor ice formation and exploited ice covered areas, indicating critical and preferable habitats respectively. Further, a significant difference in movement was found between five selected ice events with highest mean movement during an anchor ice event and lowest mean movement during an ice break up with no anchor ice formation. No significant difference in activity or movement between parr exposed to frazil ice and parr not exposed were found.