A field observation on the influence of aggressive behaviour on mating success in the European grayling

The biggest male grayling present on a spawning area was strongly territorial and developed more aggressive behaviours than smaller males. However, its spawning frequency was similar to that of Smaller males.     

Field observations on a mating attempt of a spawning grayling, Thymallus thymallus with a feeding barbel, Barbus barbus

During the spawning period of the grayling, one male was sexually stimulated by a feeding barbel and consequently exhibited the behavioural patterns of 'approach', 'qnivering' and 'dorsal fin clasping'.     

Diel pattern of first downstream post-emergence displacement in grayling, Thymallus thymallus (L., 1758)

The activity rhythm of emerging grayling, Thymallus thymallus , fry was studied under semi-natural rearing conditions, using special traps buried in the gravel. Emergence was mainly diurnal with a maximum in the first hours of daylight. Fry rested at the emergence site during the daylight and moved downstream at night, particularly during the first 3 hours of darkness. These results are compared with the known activity patterns of other salmonids.     

A preliminary investigation of spawning migrations of grayling in a small stream as determined by radio-tracking

Adult grayling Thymallus thymallus migrated from 230 to 4980 m up the Aisne stream, Belgium, to spawn between 18 and 29 March, under decreasing floods, increasing temperature and low turbidity. Males ( n =4) arrived on spawning grounds several days earlier than females ( n =2), stayed there longer (10–19 v. 2–3 days), and occupied a single ground each, whereas females moved between several places. After spawning, all grayling homed precisely into the pool-riffle sequences where they were tagged in late February, and remained here until late June. These observations indicate that resident grayling are far less mobile than autumn-spawning salmonids, and that the environmental factors triggering spawning migrations resemble more closely those of spring-spawning cyprinids than of other salmonids. The implications of these restricted mobility patterns are discussed within the scope of population structure, and impact of river management.     

Complex patterns of colonization and refugia revealed for European grayling Thymallus thymallus,based on complete sequencing of the mitochondrial DNA control region

The complete mitochondrial DNA (mtDNA) control region (1043 base pairs) and 162-bp of flanking transfer RNA genes were sequenced in 316 European grayling, Thymallus thymallus, from 44 populations throughout the Western European range of the species. A total of 58 haplotypes were revealed with pairwise divergence ranging from 0.001 to 0.038. An inferred intraspecific phylogenetic tree revealed two well-supported clades within the Danube basin, one highly divergent clade in the Adriatic basin, and one large, diverse group representing most other populations. A deeply divergent haplotype fixed in the Loire basin in central France, more groups of haplotypes from distinct Danubian tributaries, and a relatively ancestral haplotype fixed in former tributaries of the Elbe in Denmark all suggest a complex pattern of interglacial and postglacial expansions originating from disjunct refugia throughout central Europe. Despite some evidence of human-mediated stock transfers, parsimony-network-based nested-clade analysis (NCA) supported specific inferences relating to corridors of postglacial expansion such as the lower Rhine (Moselle) and Elbe systems (Danish populations) serving as sources for expansion into the Baltic to the north as well as the upper Rhine and Danube to the south; and specific Rhine populations (Doller, Orbe and Reuss) serving as sources for colonization of the Rhone. The multiple divergent clades representing populations in the upper Danube, as well as the deeply divergent haplotypes found in the Adriatic and Loire basins (> 5% divergence from Asian outgroups) support the theory that European grayling have had a long history in Western Europe, pre-dating Pleistocene glacial cycles. The patterns of mtDNA divergence shown here support a perspective of rich inter- and intrabasin genetic diversity that should be protected from current trends to translocate brood stocks for rearing and release in response to declining populations, especially in southern European basins.     

Food- and habitat-segregation in sympatric grayling and brown trout

Grayling in the large reservoir Aursjøen, Norway, did not use the pelagic habitat and only trout larger than 187 mm and older than 4+ were caught there. Both species preferred the upper 8 m in the benthic habitat, but grayling were caught deeper than trout in August and September. Grayling were more closely associated with soft substratum than trout. Association with soft substratum decreased with increasing size in grayling, whereas this relationship was reversed in trout. A low number of empty stomachs indicated a low degree of food competition, but despite this the two species segregated in different key prey items—probably due to differences in mouth shapes. The key prey item for grayling was the benthic Eurycercus lamellatus , with zooplankton dominating the diet of the smallest individuals. Large trout (>300 mm) preferred the benthic Lepidurus arcticus , whereas medium trout (160–300 mm) ate predominantly the limnic-pelagic Bythotrephes longimanus , irrespective of habitat. The distribution of key prey items seemed to be the major factor controlling the habitat use, except in small trout which showed a generalist feeding pattern throughout the period. A generalist feeding pattern, a close association to coarse substratum and absence from the pelagic habitat indicated that small trout were negatively influenced by large individuals. Small grayling seemed less affected by aggressive encounters as they were less associated with coarse substratum and ate predominantly high-risk food such as zooplankton. These individuals probably did shoal in order to reduce predation risk.     

Early survival and growth in populations of grayling with recent common ancestors—field experiments

Among eight populations of grayling Thymallus thymallus that shared common ancestors 8–28 generations earlier, mean egg mortality ranged between 1·2 and 59·8%; mortality during yolk sac absorption was low (0middot;0–8middot;0%) and mean survival to swim-up was high (90–97%), with two exceptions (20% and 50%). Survival probabilities differed significantly among populations, even after statistically adjusting for size at swim-up and water depth, water velocity, gravel size and temperature. Development time from fertilization to first observed swim-up was significantly different among populations, ranging between 27 to 40 days, or 264 to 280 degree-days. Mean specific growth rates during the first external feeding period varied between 1·2 and 2·0% day^-1 among populations. Population-specific growth rates were independent of temperature. Rates of divergence were of the same order as in other salmonid studies showing rapid evolution. The phenotypic differences may be due partly to genetic differentiation among the populations.     

Population differences in early life‐history traits in grayling

In this paper we test population differences in early life‐history traits in three grayling Thymallus thymallus populations. The grayling shared ancestors some 80–90 years ago. We performed common‐garden experiments at three temperatures (mimicking population‐specific summer temperatures), and measured survival and growth rates during early development. We found significant additive genetic variance in size (length and yolk‐sac volume) measured at hatching, swim‐up and termination of the experiment, and significantly different reaction norms for growth rate and survival during the period of first feeding. In general, each population did best at the temperature experienced in nature. These differences in early life‐history traits suggest that natural selection has resulted in local adaptation in a time period of 13–18 generations.     

Habitat selection by grayling—I. Spawning habitats

Grayling spawning sites were investigated in two French rivers, the Pollon (1 year) and the Suran (2 years) and described by current velocity, water depth, and substrate composition, completed by an assessment of bottom shear stress with FST-hemispheres. A comparison was made between used and available habitats, the latter being characterized by random sampling of 300 m long (Pollon) and 510 m long (Suran) river sections, both including three riffle/pool sequences. Mean velocities observed on spawning sites did not differ significantly between rivers or years (overall mean 48–9 cm s^-1 S.D. = 11.9, range 25.8–91.7 cm s^-1, n =150). Most water depths ranged from 10 to 40 cm in both rivers, but mean depths were significantly different ( P <0.05). Substratum of spawning grounds was dominated by gravel and pebbles (2–64 mm) in both rivers. Most spawning sites (99%) were characterized by a narrow range of hemispheres (nos 9–13), i.e. a range of shear stress of about 5–16 dyn m^-2. In the Pollon, spawners between spawning acts were found in a resting pool located immediately downstream from the spawning area and characterized by slow-flowing water (mainly <20 cm s^-1) and great depth (mainly >60 cm), with cover provided by overhanging branches and tree roots.     

Intra- and interspecific life history differences in sympatric grayling and brown trout in a Norwegian reservoir

Grayling Thymallus thymallus in Lake Aursjøen, Norway, showed a remarkably uniform growth pattern throughout life, whereas brown trout Salmo trutta showed far more variation. In addition, a narrower age-length interval of maturation was found in grayling. The restricted life history variation in grayling is discussed and it is suggested that all grayling of Lake Aursjøen experience similar environmental conditions as juveniles, which induces low phenotypic variation. In contrast the existence of several spawning populations, adapted to as many as 28 different tributaries, may have created large life history variation in Aursjøen trout. Logistic models revealed that both age and length had significant, simultaneous effects on the maturation of both species. Furthermore, the sexes of trout differed in maturation patterns, i.e. males matured earlier and at smaller sizes than female conspecifics, but no difference was found between the sexes of grayling. In addition, larger sex-specific growth differences were found in trout. An absence of early maturing males in grayling and their presence in trout is discussed as a possible explanation of the restricted life history variation found between sexes of grayling. Male grayling experienced a larger mortality rate than did females, whereas no such differences were found in trout. It is suggested that grayling males invest more in reproduction than do females, due primarily to large investments in breeding behaviour. The equal mortality rates found for both sexes of trout, albeit males starting to spawn earlier than females, is probably explained by a female-selective fishing mortality.     

Suitability criteria for spawning habitat of riverine European grayling

Generalized suitability curves, developed for the spawning habitat of grayling Thymallus thymallus by combining new preference data with information available in the literature, provided optimal ranges for dominant substratum size, water depth and mean water velocity. These were 16–32 mm, 30–40 cm, and 50–60 cm s⁻¹, respectively.     

Territorial and non-territorial spawning behaviour in the bream

The spawning behaviour of bream Abramis brama was studied in 1993, in a harbour on the River Meuse, Belgium. Fish spawned from 22 to 27 April and from 11 to 14 May, when the water temperature rose to 14.5) C. The reproductive behaviour of the bream was studied within a 15 m long part of the harbour using a video camera. Territorial males with tubercles (33–43 cm total length; >5 years old) defended bank areas of diameter 80–150 cm which included spawning substratum, i.e. roots of alder and willow trees and aquatic plants. Water depth ranged from 25 to 50 cm. Non-territorial males without tubercles (24–33 cm; 3–4 years old), remained 2–4 m away from the bank. Aggressive behaviour between males was frequent and, occasionally, males with tubercles were unable to defend a territory. Mature females (25–43 cm; >3 years old), coming from the deeper water of the surrounding area, were followed by non-territorial males before spawning in territories near the bank.     

Demography of spawning grayling (Thymallus arcticus) in the Beaverlodge River,Alberta

Changes in a grayling spawning population are described that occurred in relation to both natural and man-induced events. The spawning population was monitored from 1982 to 1987 with a trap on a fishway on the Beaverlodge River, Alberta. Most of the spawning run in each year was tagged with recaptures noted in subsequent years. Male grayling grew slightly faster than females. Growth rates were variable and appeared to be quite low in years of low water flow. Grayling first spawned at 2 to 6 years of age. The majority of tagged grayling would have returned to spawn a second time after a delay of one to two years were it not for the high adult mortality. It is hypothesized that the variable time to first maturity and the delay in the second spawning is a response to highly variable juvenile recruitment. Annual mortality rates increased with age, suggesting an increased vulnerability of larger fish to angling. The population appears highly sensitive to over-exploitation, because of the high mortality rates and the delayed time to spawning of the adults.Deceased.Deceased.     

Seasonal changes in the habitat use and movements of adult European grayling in a large subarctic river

In late summer (13 August–13 September 1998), at water temperatures of 12·0–15·7° C, grayling ( n =14) stayed mainly in the riffle-section where they were captured in a large regulated river in northern Finland, moving little between consecutive days. In autumn (2–30 October 1998), at 1·7–6·7° C, the fish ( n =16) migrated to potential overwintering sites 0–14 km up- or downstream by mid October, moving mainly short distances thereafter. The daily movement rates, and the total ranges covered by the fish in late summer and autumn were 54±32 m (mean± s.d ) and 1053±1636 m, and 190±168 m and 3135±1850 m, respectively. In autumn the fish used deeper habitats (most suitable range 150–400 cm) with lower current velocities (20–80 cm s⁻¹) and finer bottom substrata (mainly sand) than in late summer (depth 100–325 cm, velocity 30–110 cm s⁻¹, and cobble-boulder substrata).     

An analysis of the spawning behaviour of the Arctic grayling Thymallus arcticus (Pallas) with observations on mating success

In the Fond du Lac River, adult male Arctic grayling defend territories on the spawning ground for up to 7 days. Females do not defend territories and do not exhibit agonistic behaviour during the breeding season.
The behaviour patterns exhibited by Arctic grayling during spawning are virtually identical to those exhibited by European grayling. The characteristic large dorsal fin of the grayling is of major importance during the spawning act.
Less than 50% of all spawning attempts proceed to completion. Interference by other fish or the improper orientation of one fish may result in one member of the spawning pair moving away. Most often however, incomplete acts are the result of the female moving away for no apparent reason. Females may initially 'test' males or may simply not be ready to spawn when approached by males. Homosexual spawning attempts were rarely observed.     

Aggregation and spawning of the humphead wrasse Cheilinus undulatus (Pisces: Labridae): general aspects of spawning behaviour

The humphead wrasse Cheilinus undulatus formed resident spawning aggregations daily after high tide at specific locations along the seaward edge of the Palau barrier reef. The location and extent of one aggregation site remained consistent for 6 years with no physical features distinguishing it from adjacent areas. Spawning was documented most months and probably occurred year round with possible seasonal and lunar variation. Spawning males arrived first at the site, followed by females and potentially small primary males. The aggregation female to male sex ratio was estimated to be between 6:1 and 10:1. A maximum of 15 males and 100–150 females were observed at the site. A male courtship posture with the anal fin pointed, the caudal fin folded down and the dorsal fin folded against the body was maintained while swimming a few metres off the bottom in view of females. When ready to spawn females rose up as the posturing male passed and the pair released gametes in a relatively sedate fashion near the surface along the shelf break. No attempted predation on spawning adults was seen. Egg predation after spawning was uncommon. On days with early to mid‐day high tides the spawning period started 2·0–2·5 h after high tide when the speed of lagoon–ocean tidal currents peaked and lasted c. 1 h. On days with later afternoon high tides, spawning occurred sooner after high tide and before current speeds peaked. Other fishes with planktonic eggs spawned at the site as pairs or small groups in a rough succession after high tide with C. undulatus, the last species to spawn.     

Secondary contact between two divergent lineages of grayling Thymallus in the lower Enisey basin and its taxonomic implications

A contact zone between two widespread divergent lineages of grayling Thymallus sp. has been identified in the lower Enisey basin (Khantaiskoye Lake) in north central Siberia (Russia). Sequences of the mitochondrial DNA control region revealed two lineages with 2·6% divergence. Haplotypes from these two lineages clearly fall within two previously described clades, one presumably corresponding to Arctic grayling Thymallus arcticus found throughout the Siberian coastal zone as well as North America, and the other corresponding to grayling found elsewhere in the Enisey basin, including Lake Baikal and its tributaries. Allelic variation at seven microsatellite loci strongly suggests reproductive isolation in sympatry between these two lineages in Khantaiskoye Lake. Integration of these new data with existing knowledge on Thymallus throughout its Siberian range supports a taxonomic revision. The currently recognized sub-specific lineages of Arctic grayling along the Siberian Arctic coast as well as grayling from North America should probably be regarded as T. arcticus . Arctic grayling, however, are limited to the coastal zone and lower reaches of the Enisey. Most of the Enisey basin, including Lake Baikal and its tributaries are occupied by another taxon, which should be recognized as Thymallus baicalensis . This perspective strictly follows evolutionary principles, eliminates the use of four sub-specific names and circumvents the illogical mosaic distribution of T. arcticus arcticus , which nevertheless does not represent a monophyletic lineage.     

Promiscuous spawning behaviour of the tropical herring Spratelloides gracilis

Spawning behaviour of the blue sprat Spratelloides gracilis was observed at shallow reefs of Kuchierabu‐jima Island, southern Japan. The fish carried out promiscuous spawning behaviour on substrata covered with algal mats mainly in the intertidal region of a shallow inlet. The spawning events occurred only at predawn (20–50 min before sunrise) and daily for c . 25 days from mid‐June to mid‐July.