The use of passive integrated transponder systems (PIT) triggered by infrared-gates for behavioural studies in nocturnal, bottom-dwelling fish species

The movements of juvenile burbot Lota lota were monitored continuously with an overall efficiency of 92·5%. The results show that passive integrated transponder (PIT) systems (or variations of them) are highly valuable for behavioural studies of small nocturnal fish species at the laboratory or mesocosm scale.     

Seasonal changes in condition indices in adult mature and non-maturing burbot, Lota lota (L.), in the north-eastern Bothnian Bay, northern Finland

The population structure and seasonal changes in condition factors of the burbot in a shallow coastal region of the north-eastern Bothnian Bay are described. The significance of the so-called rest years is examined by comparing condition indices in immature or sterile and mature burbot. The somatic condition index ( K ₂), liver index ( K ₁), intestine index ( K ₁) and gonad index ( K_g ) are determined monthly in terms of organ weight in relation to body length. Approximately 30% of the whole catch of 1052 burbot were non-maturing but were 40 cm or more in length. K ₂, K ₁ and K ₁ were lowest in the autumn, when the first sign of gonad recrudescence was observed in mature burbot. The non-maturing burbot were never in poorer condition than mature ones. As mature and non-maturing burbot dissipated their energy stores during the warmest period of the summer, it is concluded that burbot spending a rest year do not accumulate and store energy reserves over the summer for the next year, and that such rest years, if they exist, do not occur for nutritional reasons.     

Microsatellites from the burbot (Lota lota), a freshwater gadoid fish (Teleostei)

We developed 21 polymorphic dinucleotide microsatellite loci, (CA)_n and (CT)_n, for the Holarctic freshwater fish, Lota lota, using an enriched genomic library protocol. The species has an interesting life history because winter‐spawning adults migrate over long distances to form spawning aggregations, a behaviour which should maintain genetic homogeneity across large spatial scales. Availability of the reported microsatellites will facilitate the investigation of population genetic structure with regard to postglacial colonization history and conservation strategies. The primers were screened on 30 individuals from a natural population (Lake Constance, southern Germany), revealing three to 24 alleles per locus with expected heterozygosities ranging from 0.48 to 0.93.     

Diet, prey selection, and growth of larval and juvenile burbot Lota lota (L.)

The diet, prey selection, and growth of larval and juvenile Oneida Lake burbot, Lota lota (L.), was investigated from the time of first hatch in mid-April until their disappearance from the pelagic zone at the beginning of June. Mean length increased exponentially from 3–20 mm on 18 April to 15–00 mm on 29 May. The number and size of prey in burbot stomachs, and the prey size most selected by burbot increased as they grew. Prey width, not prey length, limited the size of prey ingested. The smallest burbot ate and selected highly for the largest prey they could ingest, but older burbot did not. As burbot grew, prey selection was highest first for the rotifer Asplanchna , followed by copepod nauplii, then cyclopoid copepods. Daphnia and calanoid copepods and cyclopoid copepods were selected to similar degrees by 29 May. For a given size, however, cyciopoid copepods were selected more strongly than any other prey type from 18 to 29 May. There were no significant differences in prey selection among offshore, nearshore, and onshore habitats, nor among depths in the offshore habitat.     

Does the burbot,Lota lota,have rest years between normal spawning seasons?

A large number of sterile burbot ( Lota lota ) have been recorded on the northern coast of the Bothnian Bay (29–93%) and in Lake Kemijärvi in northern Finland (44%). A suggested hypothesis is that the burbot needs one or more rest years between spawning seasons to restore the fat reserves in its liver. A comparison made here between the three burbot populations (brackish water, lake and river), did not confirm this hypothesis. The somatic condition index, liver index and intestine index of the normally-spawning river burbot, in which the percentage of non-spawning fish was 14%, were considerably lower than those in spawned or sterile coastal or lake burbot, so that poor nutrition state did not result in sterility or rest years.     

Acoustic Repertoire of Spawning Cod, Gadus morhua

We examine the vocal repertoire of spawning cod, Gadus morhua. Fish captured in northern Norway were allowed to spawn in tanks and we recorded sound during the spawning period. The cod's grunt repertoire contained more variation than previously suggested. Half of the grunts lasted more than 200ms including one grunt lasting nearly 1s and consisting of 52 pulses, which is far beyond previous reports. Moreover, increasing repetition period and increasing duration of pulses within a grunt from the first pulse towards pulses at the end of the grunt, has previously not been described. On the other hand, no knocks or series of knocks, and on average only one grunt per hour suggest that cod are less versatile vocalists than closely related gadid species, such as haddock, Melanogrammus aeglefinus.     

A spatial analytical approach for selecting reintroduction sites for burbot in English rivers

1. Availability of suitable habitat is a prerequisite for species reintroduction success, and to ensure population persistence, investigations of a species’ habitat utilisation throughout its life history should be conducted as part of a feasibility study. 2. Habitat utilisation models for burbot, Lota lota, developed using data from field studies conducted in France and Germany and information from the literature were used to assess the feasibility of reintroducing burbot into rivers of its former native range in eastern England. 3. Per cent tree roots, aquatic vegetation and flow types were important predictors of adult burbot abundance. Furthermore, the habitat utilisation models were supplemented with information from the literature, which suggested that off‐channel habitat such as wetlands and backwaters is important for spawning and nursery stages. 4. An assessment of the habitat availability in the rivers of the burbot’s former native range using variables related to spawning and nursery and adult life stages showed that although adult habitat was widely distributed, the availability of spawning and nursery habitat was less abundant, potentially limiting successful reestablishment. 5. Potential suitable habitat was concentrated in the central and southern areas of the species’ former English distribution. Overall, rivers of the burbot’s former range potentially afford suitable habitat to sustain a reintroduced population. However, sites should be preferentially selected on the basis of having appropriate spawning and nursery areas.     

Diffusive transport in Stokeslet flow and its application to plankton ecology

In this paper we consider the advective/diffusive transport of a solute near a hovering zooplankter. We approximate the fluid flow with that of a Stokeslet, corresponding to the plankter exerting a point force on the water, and assume that the plankter acts as a point source for the transported solute, located at the same point as the force. We find an analytical expression in closed form for the steady-state concentration of the solute. We also discuss the situation where the plankter performs Brownian motion. Finally we apply the results to the courtship of the marine copepod Pseudocalanus elongatus, where the male performs a mating dance below the hovering female. For this situation, our model supports the hypothesis that the mating dance is guided by the plume of a signalling pheromone.