The deposition and mortality of the eggs of the Baltic herring Clupea harengus membras L., on different substrates in the south-west archipelago of Finland

The environmental factors affecting the deposition and mortality of the eggs of the spring-spawning Baltic herring were studied in the inner Archipelago Sea of south-western Finland. On four spawning grounds, 27 study squares (area 1 m²) were surveyed by divers. In each square, one quantitative egg sample was taken and the following data were recorded: depth, temperature, bottom quality of the square and under the eggs, egg substrate, cover (%) of plants and/or the bivalve Mytilus edulis , and the heterogeneity of the environment, expressed as the total number of all bottom materials, plants and Mytilus found in the square.
Eggs were found in the depth zone of 1–4 m. Their density ranged from 6000 to 2·3 millions of eggs per square metre. Egg number had a significant negative correlation with both depth (r=-0·545, P <0·01, d.f. = 25) and temperature of the sea water ( r =-0.479,. P <0·01,d.f. = 25), and a positive correlation with the total cover (%) in the squares ( r = 0·375, P < 0·05, d.f. = 25).
The highest numbers of eggs were found on Cladophora glomerata, which the most preferred spawning substrate of those present. Mortality of the eggs varied according to the substrate. In eggs attached to Cladophora, Potamogeton and Mytilus, the proportion of dead eggs was 0.15·5%; in those attached to red algae it was significantly higher ( Furcellaria , 5·0–63·2%; Phyllophora , 0–95·2%).     

Population structure of Atlantic herring, Clupea harengus L.

During the last decade, genetic studies have been carried out on samples of Atlantic herring, CIupea harengus L., from the Baltic, North Sea, British Isles, Norwegian sea-waters and in the western part of the North Atlantic Ocean. Based on direct comparisons of samples drawn from several areas, the available information on allozyme variation was compiled into a comparable data set and analysed for population structure and genetic distance. The results are discussed in relation to the present stock model for herring.     

Influence of temperature on evasive responses of Atlantic herring larvae attacked by yearling herring, Clupea harengus L.

Predation encounters were staged in the laboratory between yearling herring, Clupea harengus L., 66 to 104 mm t.l. , and herring larvae, 8 to 30 mm t.l. ., at 8,11 and 14 o C. Video records were used to quantify prey behaviour. Prey responsiveness, reactive distance, response latency, and apparent looming threshold were not affected by temperature. Response speeds increased with temperature. Predator error rate and capture success showed no consistent thermal effects. Although the experiments could not fully evaluate the influence of temperature on the predators, results suggest that the predator's performance largely governs the outcome of an attack on a larva and that higher temperatures favour the predator by increasing the frequency of its encounter with prey.     

Routine respiration rates of Atlantic mackerel, Scomber scombrus L., and herring, Clupea harengus L., at low activity levels

Once adapted to the captive environment, mean minimum respiration rates were 118 mgO₂ kg⁻¹ h⁻¹ for mackerel, body length ( b.l ) range 290 to 380 mm, at 11.1o C at a swimming speed of 0.6 b.l. s¹ and 93 mgO₂ kg⁻¹ h¹ for herring, length range 255 to 310 mm, at 9.3° C at a swimming speed of 0.3 b.l. s¹.     

A SCUBA-diving investigation of Baltic herring (Clupea harengus membras L.) spawning grounds in the Askö-Landsort area, northern Baltic proper

In a spawning area survey in the Askö area, northern Baltic proper, undertaken in the beginning of summer 1978, 100 randomly established and sampled transects were studied by diving. Herring spawn was found at 45 of the transects. The eggs were usually found on Pilayella littoralis , a filamentous brown algae, at the more exposed transects. Eggs were only found down to a depth of 11 m. In a neighbouring oil spill area spawn were found at only four out of 20 transects. Of eggs taken to the laboratory for hatching, 54% of those from the unaffected area hatched but only 25% of those from the oil spill area.     

Vertical migrations of herring,Clupea harengus,larvae in relation to light and prey distribution

Synopsis The influence of light and prey abundance on the vertical distribution of herring larvae was evaluated by three investigations made under calm weather conditions in the North Sea off the Scottish coast. The investigations took place at different time after hatching and the vertical distributions of three size groups of larvae (mean sizes 8,15 and 19 mm) were related to time of day and the vertical distribution of copepods. No migratory behaviour of copepods was observed but their vertical distribution differed between investigations. In the investigation on intermediate sized larvae, copepod density peaked at the pycnocline (40 m). Larvae concentrated at this depth at noon. At dawn and dusk larvae migrated towards the surface and the vertical distributions fluctuated semidielly. In the two other investigations, copepods were homogeneously distributed in the water column and after migration towards the surface at dawn larvae stayed in the upper water column during the day. The observations suggest that the daytime vertical distribution of larvae in calm weather is mainly determined by feeding conditions: the larvae move to depths were light is sufficient for feeding, and refinement within that zone is made according to a compromise between optimal light conditions for feeding and optimal prey densities.     

Inheritance of allozymes in Atlantic herring (Clupea harengus harengus)

Progeny from single pair crosses of Atlantic herring were examined to determine the heritability of genetic variation at seven polymorphic allozyme loci. Mendelian inheritance of codominant autosomal alleles was established for IDH-2, LDH-1, LDH-2, ME-2, PGM-1, and PGI-2. This demonstration of Mendelian inheritance is essential for accurate interpretation of allozymic variation among natural populations of this pelagic species.     

The relative profitability of particulate- and filter-feeding in the herring, Clupea harengus L.

Analysis of laboratory video-recordings of herring feeding by biting and filtering on Calanus finmarchicus and three sizes of Artemia enabled the capture rates of the two methods to be estimated at different prey concentrations. At low concentrations the fish feed by selective capture of individual particles, but the capture rate achievable by this method is constrained by the maximum rate at which they can bite. Filter-feeding is not subject to this constraint because capture rate is directly proportional to prey concentration and above a critical prey concentration its capture rate exceeds that of biting. The possession of two feeding methods allows the fish to maximize prey intake over a wide range of concentrations and the phenomenon of switching between feeding methods can be explained by their relative profitabilities at different concentrations. The observation that less than 50% of fish are filtering when capture rates by the two methods are equal suggests that filtering is energetically more costly than biting. Estimates of the energy cost of filtering indicated that it may be from 1.4 to 4.6 times higher than that of biting.     

Endurance at intermediate swimming speeds of Atlantic mackerel, Scomber scombrus L., herring, Clupea harengus L., and saithe, Pollachius virens L.

Endurance and swimming speed were measured in mackerel, herring and saithe when they were induced by the optomotor response to swim at prolonged speeds along a 28-m circular track through still water in a 10-m diameter gantry tank. The maximum sustained swimming speed ( U _ms was measured as body lengths per second ( b.l.s ⁻¹) for each species and for saithe of different size groups. Herring with U _ms of 4.06 b.l.s ⁻¹ (25.3 cm, 13.5°C) were the fastest, mackerel U _ms was 3.5 b.l.s ¹ (33 cm, 11.7°C) and saithe (14.4°C) showed a size effect where U _ms at 25 cm was 3.5 b.l.s ¹ and at 50 cm 2.2 b.l.s ¹. When swimming at speeds higher that U _ms, all three species showed reduced endurance as speed increased. How the curved track reduces the swimming speed is discussed.     

The growth and mortality of larval herring, Clupea harengus L., in the River Blackwater Estuary, 1978–1980

Herring larvae were sampled in the Outer Thames Estuary and the River Blackwater Estuary in the springs of 1978, 1979 and 1980. Data were collected on larval stage, yolk sac and post yolk sac, larval length and total larval numbers. Newly hatched larvae were 6.8±0.5 mm long and the growth rate of yolk sac larvae was estimated at 0.18 mm d⁻¹ ( L = 6.8±0.186 t ). The growth rate of post yolk sac larvae increased to 0.43mm d⁻¹ ( L = 11±48.0±43 t ). Mortality estimates, derived from total numbers in the summed estuary segments, varied between the years and the cohorts within the year. In 1979 the mortality rates were 0.061 d⁻¹ and 0.074 d⁻¹ for the two cohorts. The mean size of the larval population was estimated at 2.48×10⁹ (1.63–3.77 × 10⁹) which agreed well with population size estimates from egg laying and from catch in numbers at age together with estimated fishing mortality rates.     

Detection of small bioactive peptides from Atlantic herring (Clupea harengus L.)

Recent research has shown that fish residual materials contain a range of components with interesting biological activity. Therefore, there is a great potential in the marine bioprocess industry to utilize these by-products as starting material for generating more valuable products. The aim of the present study was to search for bioactive peptides (in particular small natural bioactive peptides with molecular weight lower than 10 kDa) in Atlantic herring (Clupea harengus L.) by-products such as skin and more general residual materials. By such means a range of peptides with claimed interesting biological activities was found. Herein the activity of the detected bioactive peptides and strategies for isolating peptide fragments containing the bioactive motif is discussed. Identification of bioactive peptides in crude peptide/protein sources (skin and residual materials) was performed directly using a combination of mass spectrometry (Orbitrap), bioinformatics and database search. This method was a good angle of approach in order to map the potential in new species and species that have been very little studied.     

Effect of different holding regimens on the intestinal microflora of herring (Clupea harengus) larvae.

The aerobic intestinal microflora of 2-week-old herring (Clupea harengus) larvae was characterized by using conventional microbiological methods and electron microscopy. Larvae were hatched and kept in filtered seawater or in seawater with penicillin and streptomycin. The gastrointestinal tract of herring larvae is essentially a straight tube divided into two compartments. Light microscopy revealed bacteria present in a progressively increasing amount throughout the length of the gastrointestinal tract from esophagus to anus. The posterior region of the intestinal lumen appeared completely occluded with bacteria. The intestinal microflora consisted mainly of members of the genera Pseudomonas and Alteromonas in the larvae incubated in filtered seawater, whereas Flavobacterium spp. dominated in larvae exposed to antibiotics. The intestinal microflora of untreated fish larvae was sensitive to all tested antibiotics, whereas multiple resistance was found in the intestinal microflora of the group given antibiotics. Thus, a dramatic change in the microflora resulted from incubation with antibiotics. Nonpigmented yeasts were detected in both larval groups. Ciliated epithelial cells were observed in the midgut, probably propeling bacteria towards the hindgut, where endocytosis of bacteria has been demonstrated. These findings suggest that transport and sequestering mechanisms resembling those of invertebrates may be found in the gut of fish larvae. The possible significance for larval health and nutrition is discussed.     

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.     

Long-term survey data (1965-1972) on the occurrence of Anisakis larvae (Nematoda: Ascaridida) in herring, Clupea harengus L., from the North Sea

The occurrence of larval Anisakis in North Sea herring was examined during the period 1965-1972 using a sampling method which yielded comparable data for all eight years. Data on abundance of infestation in several herring stocks pointed to remarkable fluctuations over the study period with an increase in the period 1966-1968 followed by a decrease in the period 1968-1972. Of various hypotheses that may explain this situation, it is concluded that changes in the migration behaviour of the herring may be responsible. Other data and statistics are discussed with special reference to variations in infestation level in different samples and to the occurrence of adult nematodes in marine mammals.     

Electrophoretic identification of Anisakis sp. larvae (Ascaridida: Anisakidae) from Clupea harengus L. in Baltic Sea

On the basis of electrophoretic studies carried out on 15 gene-enzyme systems, 80 Anisakis sp. larvae from the herring Clupea harengus, fished in South Baltic Sea and Gdanisk Bay, were identified as Anisakis simplex B. This is the first record of Anisakis simplex B in the Baltic Sea. The spawning migration of the herrings from the North Sea to the Baltic Sea and the distribution of A. simplex B are briefly discussed.     

Effect of different holding regimens on the intestinal microflora of herring (Clupea harengus) larvae.

The aerobic intestinal microflora of 2-week-old herring (Clupea harengus) larvae was characterized by using conventional microbiological methods and electron microscopy. Larvae were hatched and kept in filtered seawater or in seawater with penicillin and streptomycin. The gastrointestinal tract of herring larvae is essentially a straight tube divided into two compartments. Light microscopy revealed bacteria present in a progressively increasing amount throughout the length of the gastrointestinal tract from esophagus to anus. The posterior region of the intestinal lumen appeared completely occluded with bacteria. The intestinal microflora consisted mainly of members of the genera Pseudomonas and Alteromonas in the larvae incubated in filtered seawater, whereas Flavobacterium spp. dominated in larvae exposed to antibiotics. The intestinal microflora of untreated fish larvae was sensitive to all tested antibiotics, whereas multiple resistance was found in the intestinal microflora of the group given antibiotics. Thus, a dramatic change in the microflora resulted from incubation with antibiotics. Nonpigmented yeasts were detected in both larval groups. Ciliated epithelial cells were observed in the midgut, probably propeling bacteria towards the hindgut, where endocytosis of bacteria has been demonstrated. These findings suggest that transport and sequestering mechanisms resembling those of invertebrates may be found in the gut of fish larvae. The possible significance for larval health and nutrition is discussed.     

Responsiveness of selected condition measures of herring, Clupea harengus, larvae to starvation in relation to ontogeny and temperature

A laboratory experiment was performed to study the responsiveness of selected condition measures to starvation in herring, Clupea harengus, larvae in relation to temperature and ontogeny. The larvae at two intervals of development, i.e. stage 1 larvae with initial exogenous feeding and stage 2 larvae with established feeding prior to notochord flexion, were reared at three temperatures (5, 8 and 11°C) and subjected to sub-lethal durations of starvation. Temporal changes in standard length, dry weight, DNA concentration (% of dry weight), RNA concentration (% of dry weight), Fulton's condition factor (CF) and RNA/DNA were assessed and compared with fed controls. Starvation led to decreases in dry weight, CF, RNA concentration and RNA/DNA, while it led to an increase in DNA concentration. Higher responsiveness to starvation was observed at higher temperatures, and the magnitude of the changes was higher in stage 2 larvae. The shortest latency in starvation response was found with respect to RNA/DNA which was length independent in the size range studied. RNA/DNA was also significantly related to average DNA growth rate, and the model for DNA growth rate was, SGRDNA=4.49 RNA/DNA + 7.14 T – 0.42 T2 – 37.5 ; n=32, r2=0.85, p < 0.001). While the model seemed to adequately represent the average temperature dependent DNA growth, a relatively low classification success made it unsuitable for depicting individually starving larvae. Critical levels in DNA concentration can be used (2.2% for stage 1 larvae, 2.9% for stage 2 larvae) to differentiate starving larvae (after 3 – 5 days) from feeding larvae. RNA/DNA was the most sensitive and suitable condition index studied in detecting early starvation of herring larvae.     

Dispersion and mortality of yolk-sac herring (Clupea harengus L.) larvae from a spawning ground to the west of the Outer Hebrides

A patch of herring larvae located within 24 h of hatching froma spawning bed on the shelf west of the Outer Hebrides, wasfollowed for 7 days. Dispersion of the larvae was modelled usingsimple turbulent diffusion theory. The mortality rate, estimatedfrom the rate of decrease in the total population size, was–2% day^–1 over the tracking period which is verymuch less than rates calculated for herring larvae in otherareas by previous investigators. Successive observations ofthe length, weight, and the incidence of food in the intestinesof larvae, indicated that feeding commenced 5 days after hatchingand that the growth rate was 0.17 mm day^–1.