Maximum daily ration and the pattern of food consumption in haddock, Melanogrammus aeglefinus (L.), and dab, Limanda limanda (L.)

Food intake was measured under conditions of continuous food availability for haddock, Melanogrammus aeglefinus (L.), and dab, Limanda limanda (L.). Haddock consumed approximately 75% of all food during the day, with a peak of feeding at dusk and an inferred peak at dawn; peaks of feeding were associated with larger meals. By contrast, dabs were mainly night-time feeders with daily consumption rates that were approximately 40% lower than those shown by haddock. Comparison of haddock maximum daily ration with published estimates of consumption in the wild indicate that wild haddock feed at between 15 and 22% of their maximum capacity. Using published data on gastric evacuation, the relationship between meal size and stomach residuum was investigated. There was no detectable relationship between these two variables.     

Predation on northern shrimp (Pandalus borealis) by three gadoid species

Northern shrimp (Pandalus borealis) is targeted by commercial fisheries, but is also an important prey in the marine food web. In this study, stomach content data were used to study predation on shrimp by three gadoid species, cod (Gadus morhua), haddock (Melanogrammus aeglefinus) and whiting (Merlangius merlangus), in six inshore areas around Iceland. The results showed that shrimp was more important in the diet of cod compared with the other two predators. However, the overall predation pressure was similar for cod and haddock due to the high abundance of haddock. Therefore, even though shrimp is not the primary source of food for haddock, this species can have a substantial effect on shrimp stocks when haddock abundance is high. In addition, while cod and haddock did not select for any particular size of shrimp, whiting seemed to preferentially target juvenile shrimp. The results suggest that due to the overall effects of these three predators on shrimp stocks, gadoids need to be included in the management of shrimp stocks as predation is one of the major drivers in the development of this important prey stock.     

Aspects of the biology of the plerocercoid of Grillotia erinaceus (van Beneden, 1858) (Cestoda: Trypanorhyncha) in haddock Melanogrammus aeglefinus (L.)

From one to thirty Grillotia erinaceus plerocercoids were found in 3714 of 8228 haddock Melanogrammus aeglefinus caught in the northern North Sea, to the north and west of Scotland and at Faroe. Plerocercoids were also found in 30 of 64 cod from Aberdeen Bay, and in 44 of 55 saithe from the Firth of Clyde. In haddock, most plerocercoids occurred encysted along the intestine, and their frequency fitted a negative binomial distribution. Incidence and intensity of infestation increased with host age and there was no host sex difference in incidence. Three maturity stages were recognized, the proportions of which were consistent between haddock length groups. No precipitin bands developed in gel diffusion tests using live plerocercoids and sera from infested and uninfested haddock. Attempts to transfer plerocercoids between haddock were unsuccessful. Speculations are made on the possible course of the life-cycle.     

Predation of whiting and haddock on sandeel: aggregative response, competition and diel periodicity

The predation of haddock Melanogrammus aeglefinus and whiting Merlangius merlangus on sandeel Ammodytes marinus was investigated based on intensive sampling [performed with a bottom trawl (GOV) equipped with a small meshed codend cover; sediment samples were taken with a van Veen grab] in a restricted area of c . 15 × 20 nautical miles in the northern North Sea during a 5 day period in July 1996. The analysis of the spatial distribution of predators revealed a pronounced aggregation of whiting in the south‐west part of the area, where sandeel catches were also highest. This pattern was thought to be the result of an aggregative behaviour of whiting. The sandeel concentration most likely reflected a restricted patch of coarse sediment of the preferred grain size for sandeels to bury in. In haddock the aggregation was less obvious. Both predators fed almost exclusively on sandeel in the south‐west part of the area with haddock stomachs containing more sandeel than whiting stomachs. The stomach contents in both predators increased rapidly during the night, indicating that the predators were targeting burying sandeels. This would explain the competitive advantage of the benthivorous haddock.     

The ability of gadoids to take advantage of a short-term high availability of forage fish: the example of spawning aggregations in Barents Sea capelin

During 11 March to 4 April 2002, the distribution of Barents Sea capelin Mallotus villosus along the coast of Finnmark, northern Norway, was covered four times by combining acoustic survey with trawling, synoptically and simultaneously sampling capelin and its main fish predators; cod Gadus morhua, haddock Melanogrammus aeglefinus and saithe Pollachius virens. The surveys demonstrated how these gadoid predators were able to exploit such a short‐term abundance of forage fish. The predator aggregation as well as the stomach fullness and proportion of capelin in their diet followed the capelin spawning migration, increasing in areas and periods with increasing capelin abundance. Capelin clearly constituted most of the biomass in stomachs of cod (97%), haddock (87%) and saithe (96%). The stomach fullness was highest in cod and lowest in haddock, although in areas with low capelin abundance, saithe had more capelin in their stomachs. The total length (L_T) of capelin in predator stomachs increased with predator L_T, but the proportion of capelin in the diet was not influenced by predator L_T. The capelin in predator stomachs was significantly smaller than capelin in the trawl hauls, also when compared within the same sex, indicating feeding selectivity towards weaker individuals. Female capelin, being significantly smaller than the males, predominated in the diet of haddock, whereas in cod and saithe the sex ratio was more equal. Male capelin predominated in the predator diet during the pre‐spawning period, whereas the females predominated as the spawning commenced. During the overall study period, most of the female capelin in predator stomachs was in a pre‐spawning or a spawning stage, whereas the majority of the males appeared to be spent. Regardless of sex, the percentage of spent, relative to pre‐spawning or spawning capelin in the diet of the predators, followed the capelin spawning dynamics, increasing with time as the spawning progressed.     

The influence of maternal length and age on the size and weight of the eggs and the relative fecundity of the haddock, Melanogrammus aeglefinus, in British waters

The diameter and dry weight of the eggs of haddock, Melanogrammus aeglefinus , are positively correlated with fish length. The correlations are largely due to the fact that many of the smaller fish that were sampled were 2 years old, and the eggs of these young haddock, which can be regarded as precocious spawners, are significantly smaller and lighter than those of older fish. The relative fecundity of 2–year–old haddock (274 eggs g⁻¹) is also lower than that of the other age classes (493 eggs g⁻¹); this has important implications for the estimation of egg production from female spawning stock biomass. It is pointed out that in some years precocious spawners represent a large component of the North Sea haddock spawning stock. When the annual egg production of this stock is calculated, it may be appropriate to apply a weighting factor to the number of eggs contributed by the 2–year–olds, on the assumption that the small eggs of these fish produce larvae that are less viable than those of older haddock.     

Occurrence of Bucephaloides gracilescens metacercariae in three species of gadoid fish

Bucephaloides gracilescens metacercaria is a common encysted trematode parasite of whiting, Merlangius merlangus (L), haddock, Melanogrammus aeglefinus (L), and hake, Merluccius merluccius (L), in the Irish Sea. The incidence of infection over an 18-month period was uniformly high (whiting, 95%; haddock and hake, 100%). The major site of infection in all three hosts was the cranial fluid surrounding the brain. Large numbers of cysts were also found embedded in the spinal nerves posterior to the anus in haddock and hake and in the auditory capsules in whiting and haddock. Other sites of infection included the spinal canal, cranial nerves (V, VII, VIII, X), eye muscles, orbits and nasal region. Results are discussed in the light of previous records of gasterostome trematodes in the Gadidae.     

Distribution and diet of 0-group cod (<Emphasis Type="Italic">Gadus morhua</Emphasis>) and haddock (<Emphasis Type="Italic">Melanogrammus aeglefinus</Emphasis>) in the Barents Sea in relation to food availability and temperature

Distribution of 0-group cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) in August–September 2005 and 2006 was mainly restricted to the Atlantic waters of the western and central areas of the Barents Sea. The main distribution of 0-group fish overlapped largely with areas of high biomass (>7 gm⁻² dry weight) of zooplankton. The copepod Calanus finmarchicus and krill Thysanoessa inermis, which are dominant zooplankton species in both Atlantic and boreal waters of the Barents Sea, were the main prey of 0-group cod and haddock. The main distribution, feeding areas and prey of 0-group cod and haddock overlapped, implying that competition for food may occur between the two species. However, though their diet coincided to a certain degree, haddock seems to prefer smaller and less mobile prey, such as Limacina and appendicularians. As 0-group fish increased in size, there seems to be a shift in diet, from small copepods and towards larger prey such as krill and fish. Overall, a largely pelagic feeding behaviour of 0-group cod and haddock was evident from this study.     

Do haddock select habitats to maximize condition?

Haddock Melanogrammus aeglefinus in the North sea increased their distributional range when more abundant, but this density dependent habitat selection (DDHS) explained only a small part of the year‐on‐year variation in distribution patterns. The condition of haddock was examined at 24 sites in the North Sea in August and September 2004 and related to their abundance, to examine if the ideal free distribution theory (IFD), which assumes that organisms select habitats that maximize their rate of food intake, can be used to explain this variation in large scale distribution patterns. At a given temperature, condition (hepato‐somatic index, I _H) was better at stations where haddock were most abundant. Therefore, haddock were not distributed perfectly according to the IFD in 2004. The positive correlation between abundance and I _H, however, indicated there was some habitat selection by haddock, as in the total absence of habitat selection no correlation between I _H and abundance, and no spatial variation in abundance was expected. DDHS may only explain a small part of the yearly variation in the distribution because haddock did not equalize and maximize their fitness at the scale of the North Sea. In addition, stable isotope analysis of muscle samples showed that haddock did not avoid competition for food when at high abundance by feeding at a lower or wider range of trophic levels.     

Mineral nutrition of haddock Melanogrammus aeglefinus(L.): a comparison of wild and cultured stock

The macro and trace mineral composition of vertebrae and muscle in wild and cultured haddock Melanogrammus aeglefinus was determined. Results indicated that haddock deposit c . 10% higher amounts of mineral than salmonids. Based on distribution between the analysed tissues as well as concentration differences, the minerals in wild and cultured haddock were divided into four categories: (1) As, Mn, Na, S and Zn concentration did not show any significant ( P  > 0·05) variation in both muscle and vertebrae; (2) Cr, Co, Mg, Mo and Si concentrations in wild and culture stocks muscle did not vary but vertebrae concentration showed significant differences ( P  < 0·05); (3) Ca and Cu concentration varied in muscle while remaining the same in vertebrae; (4) Al, Ba, Fe, P, K and Sr concentration showed a significant difference in both muscle and vertebrae. Vertebrae P content of cultured haddock was lower than that of wild fish whereas muscle P content was relatively high in cultured fish. Vertebrae and muscle Fe content of cultured haddock was significantly higher than in wild fish. The Mg, K, Co and Cr concentrations in vertebrae were significantly higher in wild haddock than in cultured fish, whereas Mo and Al levels were low. These differences in trace element composition of wild and cultured haddock were probably related to differences in food source and therefore the mineral composition of the diet. The nutritional significance of these findings is discussed.     

Differences between male,female and juvenile haddock (Melanogrammus aeglefinus L.) sounds

Female and juvenile haddock make sounds, as well as males. Examination of the sounds from different sexes indicates that the sound waveform is a function of fish maturity and it is gender-specific. Immature fish sounds were found to be made up of two pulses with similar frequencies and opposite polarities. Females produced two pulses with the same polarity, the first pulse having a higher frequency than the second. The acoustic characteristics of juvenile, female and male haddock sounds are compared. Sexual dimorphism in the mass of the drumming muscle mass has also been investigated. Female haddock possess less well-developed drumming muscles than males throughout the whole year. A significant difference in drumming muscle mass was observed not only in males but also in females at different seasons. A positive relation between drumming muscle mass and fish size has been highlighted in both male and female fish. The physical parameters of the sound units emitted by juveniles, females and males, which are likely affected by physiological condition and maturity stage, are discussed in relation to the sound-producing mechanism.     

Observations on the food and diel feeding behaviour of pelagic O-group gadoids in the northern North Sea

The diets and diel feeding behaviour of six O-group gadoid species are described, the cod Gadus morhua (L.), the haddock Melanogramus aeglefinus (L.), whiting Merlangius merlangus (L.), saithe Pollachius virens (L.), Norway pout Trisopterus esmarkii (L.) and the blue whiting Micromesistius poutassou (R.). There were differences, in the main food groups selected by each species with respect to the type, size and number. The main prey consumed did not vary with depth. Cod, saithe and Norway pout had only one period of feeding activity whereas haddock and whiting apparently had two. The diets of haddock and whiting varied in association with these two periods. It is suggested that the differences between the diets were the result of each species having a different feeding behaviour which reflects that adopted in adult life.     

Isolation and Characterization of Tetranucleotide Microsatellites from Atlantic Haddock (Melanogrammus aeglefinus)

Five tetranucleotide microsatellite loci developed from Atlantic haddock (Melanogrammus aeglefinus) are presented. Loci were isolated using a modified magnetic bead-hybridization selection procedure that enriched for tetranucleotide microsatellites. Loci were polymorphic (3–99 alleles per locus; mean, 33.2) and exhibited high levels of observed heterozygosity (0.07–0.99; mean, 0.73) in a sample of 70 haddock collected from the Scotian Shelf in the Northwest Atlantic Ocean. Primer sets for 5 tetranucleotide microsatellites, originally developed from cod (Gmo34), were also tested in Atlantic haddock; one pair yielded readily detectable product and was variable in the population assayed (29 alleles; heterozygosity, 0.96). These loci are suitable for kinship analyses in aquaculture-related applications, and are potentially useful for resolving population structure in the wild.     

Histological and morphological evaluations of the digestive tract and associated organs of haddock throughout post-hatching ontogeny

At hatching, the oesophagus of haddock Melanogrammus aeglefinus lacks goblet cells, the intestine is a simple undifferentiated tube, the liver is present as a rounded mass caudal to the heart, and numerous zymogen granules are present in the pancreas. The first intestinal convolution appears at day 2, at the posterior end of the digestive tract. The oesophagus displays alcian blue and PAS positive mucus secreting cells on day 12, which become numerous by day 15. By day 18, epithelial cells of the posterior intestine show evidence of protein absorption in the form of supranuclear vacuoles. The swimbladder inflates in 50% of the larvae by day 22, although inflation rate is highly variable. By day 35, or 10 mm, a pyloric caecal ridge appears which separates the presumptive stomach, which is now showing evidence of gastric gland formation, from the intestine. This marks the beginning of digestive features characteristic of the juvenile stage.     

Comparison of antimicrobial activity in the epidermal mucus extracts of fish

The mucus layer on the surface of fish consists of several antimicrobial agents that provide a first line of defense against invading pathogens. To date, little is known about the antimicrobial properties of the mucus of Arctic char (Salvelinus alpinus), brook trout (S. fontinalis), koi carp (Cyprinus carpio sub sp. koi), striped bass (Morone saxatilis), haddock (Melanogrammus aeglefinus) and hagfish (Myxine glutinosa). The epidermal mucus samples from these fish were extracted with acidic, organic and aqueous solvents to identify potential antimicrobial agents including basic peptides, secondary metabolites, aqueous and acid soluble compounds. Initial screening of the mucus extracts against a susceptible strain of Salmonella enterica C610, showed a significant variation in antimicrobial activity among the fish species examined. The acidic mucus extracts of brook trout, haddock and hagfish exhibited bactericidal activity. The organic mucus extracts of brook trout, striped bass and koi carp showed bacteriostatic activity. There was no detectable activity in the aqueous mucus extracts. Further investigations of the activity of the acidic mucus extracts of brook trout, haddock and hagfish showed that these fish species had specific activity for fish and human pathogens, demonstrating the role of fish mucus in antimicrobial protection. In comparison to brook trout and haddock, the minimum bactericidal concentrations of hagfish acidic mucus extracts were found to be approximately 1.5 to 3.0 times lower against fish pathogens and approximately 1.6 to 6.6 folds lower for human pathogens. This preliminary information suggests that the mucus from these fish species may be a source of novel antimicrobial agents for fish and human health related applications.     

The genera Ceratomyxa Thélohan, 1892, Leptotheca Thélohan, 1895 and Sphaeromyxa Thélohan, 1892 (Myxosporea: Bivalvulida) in gadid fish of the Northeast Atlantic

The gall-bladders of four species of gadid fish from the North Sea and Norwegian waters were examined for myxosporeans. The host species were cod Gadus morhua L. (350 examined), haddock Melanogrammus aeglefinus (L.) (592 examined), saithe Pollachius virens (L.) (205 examined) and whiting Merlangius merlangus (L.) (368 examined). Four species of myxosporeans are redescribed from these fish. Ceratomyxa arcuata Thélohan, 1892 was the most common species and was found in whiting (42.8%) and cod (0.6%). Leptotheca informis Auerbach, 1910 was found only in whiting (6.5%). L. longipes Auerbach, 1910 was found only in haddock (6.2%). Sphaeromyxa hellandi Auerbach, 1909 was found in haddock (9.1%) and whiting (0.3%). None of the saithe examined, and no cod or haddock from Norwegian waters, was infected with these myxosporeans. All four species appear to have distributions limited to the Northeast Atlantic, with S. hellandi having a more northern distribution than the other three. The validity of reports of C. arcuata, L. informis and L. longipes from outside this area is discussed.     

Isolation of Aeromonas Sp. ATCC 29063, a Phenol-Producing Organism, from Fresh Haddock

Attempts to isolate phenol-producing organisms from stale haddock fillets failed. Several such isolates, however, were readily obtained from fresh haddock and were designated Aeromonas sp. Phenol was produced from L-tyrosine by these isolates.     

The development of haddock and Atlantic cod sperm cryopreservation techniques and the effect of sperm age on cryopreservation success

Three cryoprotectants [dimethyl sulphoxide (DMSO), propylene glycol (PG) and glycerol], two diluents (sucrose‐ and saline‐based), two sperm collection times, two freezing rates and three times between thaw and activation (0, 30 and 60 min) were tested in order to develop a protocol for the cryopreservation of sperm of haddock Melanogrammus aeglefinus and Atlantic cod Gadus morhua . The faster freezing rate resulted in extremely low post‐thaw motility in comparison to the slower freezing rate, which was successful for sperm from both gadids. In both cases, the use of PG resulted in significantly higher post‐thaw sperm motility‐recovery indices than with DMSO or glycerol, which did not differ significantly from one another. Diluent had no effect on post‐thaw sperm motility for Atlantic cod or haddock. Sperm collected at the end of the spawning season tended to have reduced post‐thaw motility compared to that collected 2 weeks after the start of spawning. A 30 min delay between thaw and activation of haddock and Atlantic cod sperm resulted in a significant decrease in sperm motility. When PG was used as cryoprotectant, sperm motility continued to decrease between 30 and 60 min post‐thaw. With DMSO or glycerol as cryoprotectant, motilities were already very low after 30 min post‐thaw and did not decrease any further after 60 min. Cryoprotectant, diluent and time between thaw and activation had no effect on mean or maximum sperm swimming speeds for either Atlantic cod or haddock sperm. Fertilization success for haddock eggs, like sperm motility, was higher with PG‐frozen sperm than DMSO‐ or glycerol‐frozen sperm. These results constitute the first reported successful cryopreservation of haddock sperm and improve on previous methods used to cryopreserve sperm from Atlantic cod.     

Effects of Substerilization Doses of Co60 Gamma Radiation on the Cold-Storage Life Extension of Shucked Soft-Shelled Clams and Haddock Fillets

Total aerobic-facultative and anaerobic (clostridia) macrocolony count data are presented, with analysis and interpretation, for both haddock fillets and shucked soft-shelled clams which received doses of from 50,000 to 800,000 rad of Co⁶⁰ gamma rays. These data indicated that haddock fillets may be maintained in good condition at refrigeration temperatures above freezing for about 1 week at 6 C, and approximately 2 weeks at 0 C, when treated with from 50,000 to 150,000 rad of ionizing radiation. In the dose range from 200,000 to 350,000 rad, the storage life may be extended up to some 2 weeks at 6 C, and 3 weeks at 0 C. Treatments in the dose range from 400,000 to 500,000 rad may defer spoilage for about 1 month, and doses of 550,000 to 650,000 rad afford protection against bacterial spoilage up to approximately 1.5 months. At the high substerilization doses of 700,000 to 800,000 rad, haddock fillets may be held for from 2 to 3 months in refrigerated storage before becoming unfit for marketing and consumption. Shucked soft-shelled clams can be held for about 2.5 weeks at 0 C and close to 12 days at 6 C, when given low substerilization doses of from 50,000 to 150,000 rad of ionizing radiation. At doses of from 200,000 to 350,000 rad, the clams may be preserved effectively for periods up to 3 weeks at 0 or 6 C, and some 6 weeks at these temperatures with doses of about 450,000 rad. With treatments of 500,000 to 600,000 rad, the storage life may be extended for some 2 months, and at doses of 650,000 to 800,000 rad the shucked clams remain in a good state of preservation for up to 3 months at temperatures of 0 to 6 C. Thus, it would appear that shucked soft-shelled clams may be maintained for significantly longer periods in refrigerated storage than haddock fillets when the same radiation treatments are applied to each product. Clostridia levels in both products were relatively low initially, and were reduced significantly by the gamma rays at the doses studied. Moreover, those clostridia that survived the radiation treatments were found to remain at safe, low levels during the various periods in refrigerated storage employed for these products, a very encouraging result from the public health, as well as commercial, standpoint.     

The effect of light intensity and spectrum on the incidence of first feeding by larval haddock

Under full–spectrum white light, feeding success of haddock Melanogrammus aeglefinus first feeding larvae, as measured both by proportion of larvae feeding and mean prey consumed, peaked at 1·7-18 μmol s^-1 m^-2. Feeding was significantly reduced at lower and higher intensities. A similar result was observed for larvae feeding under blue (470 nm) light, with significantly greater feeding success at intermediate light intensity (1·8 μmol s^-1 m^-2). When different light qualities were compared, larvae had significantly greater feeding success when exposed to blue (470 nm) light than either full-spectrum white or green (530 nm) light. Haddock larvae were capable of prey capture under all light treatments tested, indicating a necessary degree of adaptive flexibility in feeding response. The results are consistent with predisposition of haddock larvae to optimal feeding in a visual environment comparable with open ocean nursery grounds. Information on the impact of light on haddock first feeding can be incorporated into models of larval growth, survival, year-class strength and recruitment, and assist in developing husbandry protocols to maximize larval survival in aquaculture.