Growth and metabolism of adult polar cod (Boreogadus saida) in response to dietary crude oil.

The increasing human presence in the Arctic shelf seas, with the expansion of oil and gas industries and maritime shipping, poses a risk for Arctic marine organisms such as the key species polar cod (Boreogadus saida). The impact of dietary crude oil on growth and metabolism of polar cod was investigated in the early spring (March-April) when individuals are expected to be in a vulnerable physiological state with poor energy stores. Adult polar cod were exposed dietarily to three doses of Kobbe crude oil during an eight weeks period and followed by two weeks of depuration. Significant dose-responses in exposure biomarkers (hepatic ethoxyresorufine-O-deethylase [EROD] activity and 1-OH phenanthrene metabolites in bile) indicated that polycyclic aromatic hydrocarbons (PAHs) were bioavailable. Condition indices (i.e. Fulton's condition factor, hepatosomatic index), growth, whole body respiration, and total lipid content in the liver were monitored over the course of the experiment. The majority of females were immature, while a few had spawned during the season and showed low hepatic lipid content during the experiment. In contrast, males were all, except for one immature individual, in a post-spawning stage and had larger hepatic energy stores than females. Most specimens, independent of sex, showed a loss in weight, that was exacerbated by exposure to crude oil and low hepatic liver lipids. Furthermore, females exposed to crude oil showed a significant elevation of oxygen consumption compared to controls, although not dose-dependent. This study highlights the importance of the energy status of individuals for their response to a crude oil exposure.

Trade-offs between life-history traits in a coldwater fish in the Mediterranean Sea: the case of blue whiting Micromesistius poutassou.

A combination of traditional and emerging methodologies was used to assess the trade-offs between several life-history traits (linked to reproduction and condition) and parasitism in a commercially-exploited cold-water species, blue whiting Micromesistius poutassou, in the Mediterranean Sea. The use of histological and gravimetric methods revealed conflicting evidence as to the fecundity type (indeterminate or determinate) of this species. Moreover, there seem to be condition-mediated compensations between egg quality and egg quantity. The effects of parasitism on reproduction and condition are species-specific and occur mainly at high intensities of infection; they include a lower batch fecundity (affecting reproductive potential), a higher hepatosomatic index and a higher spleen-somatic index. Considering the fact that larger fish spawn more eggs and that the minimum landing size is lower than the size at maturity, these results may have implications for the future management of M. poutassou stocks in the Mediterranean Sea. Local environmental conditions may account for geographical differences regarding infection in M. poutassou. Altogether, the results support the idea that the complex trade-offs between parasitism, reproduction and condition need to be considered in order to understand the status of cold-water species such as M. poutassou.

Vertebral column deformity in adult wild haddock (Melanogrammus aeglefinus).

This study describes radiological malformations in the vertebral column of adult sexually mature wild haddock, Melanogrammus aeglefinus collected from Masfjorden, Western Norway, in 2014 and 2015. There were seven deformed fish (33% of sampled fish), five with mild deformities and two with severe deformities. The deformity types discovered were lordosis, vertebra body asymmetry, compression, fusion (ankylosis), remodelling, and haemal spine hyperostosis. The two severely deformed fish were as follows: (a) one specimen with 29 deformed vertebrae within the region vertebrae nos. 1-30, including two sites of lordosis; (b) one specimen with 15 deformed vertebrae within the region vertebrae nos. 31-52 (most caudal vertebrae). The results of this study show that wild haddock can survive severe vertebra deformities, both in the trunk and tail region, and reach adulthood and sexual maturity. Whether normal nondeformed wild conspecifics would mate and spawn with these individuals and thereby complete the life cycle of the deformed individuals is, however, unknown. A possible link between bone fracture and fish hyperostosis is discussed.

Growth and food consumption of whiting Merlangius merlangus.

In the western Baltic Sea (WBS), whiting Merlangius merlangus is the main piscivorous fish together with cod Gadus morhua. In the present study, we investigate the growth and food consumption rates of WBS M. merlangus and compare the growth rates of males and females with those of M. merlangus in the North Sea (NS). Food consumption rates are estimated directly from sampled stomach contents in the WBS using a gastric evacuation rate model and indirectly by using a static energy-budget model together with the growth rates. The results indicate that male and female M. merlangus in the WBS have similar feeding and growth strategies, while in the NS M. merlangus show more pronounced differences in food consumption and growth dynamics between the sexes. Female WBS M. merlangus grow significantly slower than their conspecifics in the NS, but there is no significant difference for males. Sexual size dimorphism is seen in both areas, but for M. merlangus in the WBS the difference is less pronounced. Food consumption rates in the WBS differ between seasons, with the lowest food intake in the first 2 quarters of the year and the highest in the 3rd quarter. No differences in consumption rates were seen between males and females, which could be related to the more similar growth pattern seen for M. merlangus in the WBS.

Unravelling growth trajectories from complicated otoliths - the case of Brazilian codling Urophycis brasiliensis.

Uncertainty regarding the age determination of the Brazilian codling Urophycis brasiliensis has hampered its stock assessment. Transverse sections of otoliths displayed up to seven (in males) and 12 (in females) alternate opaque and translucent bands that could not be conclusively validated as annuli, resulting in unrealistically high ages of first maturity (A50 ) (A50male = 4·5 years and A50female = 6 years). Therefore, growth was described by the von Bertalanffy (VB) model using an alternative approach that combined microstructure data (daily growth increments) and a fixed asymptotic total length (L∞ ). This approach was supported by applying it to two other co-occurring species, the whitemouth croaker Micropogonias furnieri and the king weakfish Macrodon atricauda, for which daily and annual ring formation has previously been validated. The sensitivity to realistic errors associated with the choice of the L∞ and the daily increment readings was shown to be low. The results show that U. brasiliensis has a fast growth rate (Kmale = 1·19 year-1 , Kfemale = 0·71 year-1 ) and early maturation (A50male = 1·1-1·5 years, A50female  = 1·6-1·8 years); typical life-history traits for a sub-tropical coastal gadiform. This novel study offers an alternative approach for age and growth reconstruction for species with complex patterns of opaque and translucent bands provided that daily growth increments in the yearlings can be counted and L∞ reliably estimated.

Timecourse of oocyte development in saithe Pollachius virens.

Wild caught North Sea saithe Pollachius virens were monitored for growth, sex steroid profiles and oocyte development pre-spawning and measured for egg size and group fecundity during the spawning season in the laboratory. Vitellogenesis commenced in late October-early November, at a leading cohort size (CL ) of c. 250 µm, after which oocytes grew rapidly in size until spawning started in February. Notably, a distinct cortical alveoli stage was virtually absent with yolk granules observed in developing oocytes at the very beginning of vitellogenesis. Little atresia was observed pre-spawning, but atretic re-absorption of remnant oocytes containing yolk granules was found in all females immediately post-spawning. As expected, concentrations of sex steroids, oestradiol-17ß (females), testosterone (both sexes) and 11-ketotestosterone (both sexes), increased pre-spawning before dropping post-spawning. The present experiment provides the first validation of sex steroid levels in P. virens. Post-ovulatory follicles were visible in histological sections from female gonads 9-11 months post-spawning, but then disappeared. Spawning commenced around a CL of c. 750 µm (700-800 µm). Hydrated oocytes (eggs) measured between 1·04 and 1·31 mm (mean = 1·18 mm) with decreasing sizes towards the end of spawning. The average estimated realized fecundity was c. 0·84 million eggs (median female total length, LT = 60 cm). Spawning lasted from 13 February to 29 March.

The diet of whiting Merlangius merlangus in the western Baltic Sea.

The diet of whiting Merlangius merlangus in the western Baltic Sea was investigated and compared to the diet in the southern North Sea. Clupeids were important prey in both areas, but especially in the western Baltic Sea where they constituted up to 90% of the diet of larger individuals. Gobies, brown shrimps and polychaetes were the main prey of juveniles in the western Baltic Sea, while a wider range of species were consumed in the North Sea. The shift to piscivory occurred at smaller sizes in the western Baltic Sea and the fish prey consumed was proportionately larger than in the southern North Sea. Estimates of prey abundance and food intake of M. merlangus are required to evaluate its predatory significance in the western Baltic Sea, but its diet suggests that it could be just as significant a fish predator here as in the southern North Sea.

Laboratory rearing of wild Arctic cod Boreogadus saida from egg to adulthood.

The techniques and protocols used to successfully capture, transport and breed Arctic cod Boreogadus saida, as well as to rear their larvae through to adulthood are summarized. Breeding B. saida will increase the opportunity to study this fish species, which is a critical part of the Arctic food web.

New records of larval stages of the eel cod genus Muraenolepis Günther 1880 (Gadiformes: Muraenolepididae) from the western Antarctic Peninsula.

Three newly discovered larval specimens of the genus Muraenolepis collected from the waters of the western Antarctic Peninsula are described. Knowledge of their natural history is sparse and information about their early life history is based on only a few larval stages. Here, the available literature on larval eel cods is reviewed, and the specimens placed in context.

Induction of gonadal maturation at different temperatures in burbot Lota lota.

A rearing experiment was conducted to test whether temperature protocols that differed from a simulation of natural conditions might induce maturation after isothermal grow-out in burbot Lota lota. Lota lota were acclimated to two different temperature regimes: low temperature (LT), close to natural temperature at 4·0° C and elevated, high temperature (HT) at 8·5° C over 40 and 27 days respectively, with all fish then wintered for 47 days. Every second fish was treated with a gonadotropin-releasing hormone analogue. Maturational competence of oocytes was assessed with a germinal vesicle breakdown assay using a novel staining strategy. In both treatments, puberty and maturational progress occurred, characterised by an elevated gonado-somatic index and advanced gonadal stages (histological analysis). Progress of gonadal maturation was reflected by elevated plasma concentrations of testosterone and 11-ketosterone in males and 17ß-oestradiol in females. Ovulation was not observed. Sperm could be activated equally across treatments. In general, LT was more effective than HT treatment, indicated by advanced gonadal stages, higher numbers of oocytes undergoing germinal vesicle breakdown in vitro and elevated sex steroid levels. Hormone treatment could improve effectiveness at HT. In conclusion, less drastic temperature regimes as previously reported in combination with hormone treatments seem sufficient to induce maturation in L. lota after isothermal grow-out.

Biannual otolith-zone formation of young shallow-water hake Merluccius capensis in the northern Benguela: age verification using otoliths sampled by a top predator.

Otoliths collected at least monthly from scat samples of Cape fur seals Arctocephalus pusillus are used to show that shallow-water hake Merluccius capensis from the northern Benguela develop three translucent zones in their first 1·5 years of life. The novel sampling approach provided otoliths that belonged to four M. capensis cohorts of approximate known age (hatched in 1996, 1998, 2002 and 2005), allowing age verification. Following spawning in austral winter, translucent zones consistently formed first in summer and autumn (T1), then in winter and spring (T2) and again in summer and autumn (T3), with no difference in appearance of the zones (biannuli) for the four cohorts considered. The second translucent zone is usually the first true annulus (year mark). It forms during July to September in fish of 15-20 cm total length (LT ). Formation of the translucent zones appears to be determined by fish length or age, rather than by exogenous cues. It is suggested that length measurements should be used to help determine the first age group; fish with a translucent zone marked at otolith lengths >7·5 mm should be termed 1 year-old fish. Ages of M. capensis used in previous stock assessment models have been overestimated. Biannuli are an unusual occurrence in fish otoliths in general, but have been observed in other Merluccius species.

Age estimation of juvenile European hake Merluccius merluccius based on otolith microstructure analysis: a slow or fast growth pattern?

The main goal of this study was to examine otolith microstructure and to estimate the age and growth of European hake Merluccius merluccius from the eastern Mediterranean Sea. One hundred and twenty-nine specimens ranging from 102 to 438 mm in total length (LT ) were used. Age estimations were based on the study of the otolith microstructure, which was revealed after grinding both frontal sides of otoliths. The enumerations of the daily growth increments (DGI) as well as their width (WDGI ) measurements were made on calibrated digital images. The number of DGI in otoliths ranged between 163 and 717. Four phases in the WDGI evolution were distinguished: (1) larval-juvenile pelagic phase, with an increasing trend in WDGI up to the 60th DGI, (2) settlement phase, with a short-term deceleration in WDGI between the 61st and 150th DGI, (3) juvenile demersal phase, characterized by a stabilization of WDGI from 151st to 400th DGI and (4) adult phase, with a decreasing trend in WDGI after the 400th DGI. Age, sex and month of formation were found to affect the WDGI in all phases, with the exception of age at the juvenile demersal phase. The power curve with intercept model described best the relationship of M. merluccius LT with age (TDGI ), according to Akaike criteria, revealing differences in growth between females [LT = 65 · 36(TDGI )(0 · 40) - 388 · 55] and males [LT = 69 · 32(TDGI )(0 · 37) - 352 · 88] for the sizes examined. The mean daily growth rates were 0·61 mm day(-1) for females and 0·52 mm day(-1) for males, resulting in an LT of 283 and 265 mm at the end of their first year of life. In comparison with previous studies on the Mediterranean Sea, the results of this study showed a greater growth rate, similar to results from tagging experiments and otolith microstructure analyses for M. merluccius in other geographic areas.

Sexual size dimorphism in three North Sea gadoids.

Existing biological data on whiting Merlangius merlangus, cod Gadus morhua and haddock Melanogrammus aeglefinus from a long-term international survey were analysed to address sexual size dimorphism (SSD) and its effect on their ecology and management. Results show that SSD, with larger females of the same age as males, is a result of higher growth rates in females. A direct consequence of SSD is the pronounced length-dependent female ratio that was found in all three gadoids in the North Sea. Female ratios of the three species changed from equality to female dominance at specific dominance transition lengths of c. 30, 35 and 60 cm for M. merlangus, G. morhua and M. aeglefinus, respectively. An analysis by area for M. merlangus also revealed length dependence of female ratios. SSD and length-dependent female ratios under most circumstances are inseparable. Higher overall energy demand as well as a higher energy uptake rate must result from the observed SSD and dimorphism in growth rates. Potential processes related to feeding, locomotion and physiology are proposed that could balance the increased energy investment of females. Potential consequences of SSD and length dependency of female ratios are the reduction of the reproductive potential of a stock due to size-selective fishing and biased assessment of the true size of the female spawning stock that could distort decisions in fisheries management.

Effects of density dependence, zooplankton and temperature on blue whiting Micromesistius poutassou growth.

Blue whiting Micromesistius poutassou mean total length at age in the north-east Atlantic Ocean was found to vary by around ±6% during the period 2004-2011 and mean mass at age by ±22% during the years 1981-2013. Linear modelling provided strong evidence that these phenotypic growth variations can be explained by trophic conditions, mainly negative density dependence and also food availability, and a negative long-term temperature effect on asymptotic size.

Sex-specific food intake in whiting Merlangius merlangus.

In this study, the topic of sexual growth dimorphism in whiting Merlangius merlangus is examined. To understand the magnitude and underlying mechanisms, North Sea International Bottom Trawl Survey (IBTS) data and two additional datasets from the third quarter of 2007 and the first quarter of 2012 were analysed. Merlangius merlangus displays distinct differences in growth parameters between males and females, with females reaching a higher asymptotic length (L∞ ) than males. To identify the mechanisms which lead to higher growth in females, the quantity and the quality of the diet of M. merlangus in the North Sea were investigated to compare the sex-specific energy uptake levels. The diet composition did not differ between the sexes, but females had higher stomach content masses than males of the same total length (LT ), and showed lower proportions of empty stomachs. Moreover, female M. merlangus had higher liver and empty stomach masses compared with males of the same size, which indicates additional sex-specific differences in the metabolic costs and energy allocation patterns. Finally, interannual differences were found in the stomach contents, the share of empty stomachs and liver masses of M. merlangus in the North Sea.

Marine heatwaves alter the nursery function of coastal habitats for juvenile Gulf of Alaska Pacific cod.

Marine Heatwaves (MHWs) can directly influence survival of marine fishes, particularly for early life stages, including age-0 juveniles during their residence in coastal nursery habitats. However, the ability of nurseries to support high fish densities, optimize foraging and growth, and protect against predators may be altered during MHWs. Gulf of Alaska Pacific cod (Gadus macrocephalus) larval, juvenile, and adult abundances declined dramatically following MHW events in 2014-2016 and 2019. To evaluate coastal nursery function during MHWs, we compared diet composition, recent growth, size, condition, and abundance of age-0 juveniles throughout their first summer before, during, and between MHWs. Diet shifted to larger prey during MHWs, particularly mysids, but diet did not appear to influence growth. We observed faster growth rates during MHWs, yet even when accounting for growth, we could not explain the higher body sizes observed in August during MHWs. Together with lower abundance and the near absence of small fish in the nursery by August during MHWs, these patterns highlight potential for size-selection and a reduced ability of nursery habitats to buffer against environmental variability during MHWs, with only a small number of large "super survivors" persisting through the summer.

Influences of bioavailability, trophic position, and growth on methylmercury in hakes (Merluccius merluccius) from Northwestern Mediterranean and Northeastern Atlantic.

Methylmercury (MeHg) determinations in hake, its food-chain, and the surrounding waters and sediments allowed us to show that the higher length or age normalized mercury concentrations of Northwestern Mediterranean (Gulf of Lions: GoL) muscle hakes compared to its Northeastern Atlantic (Bay of Biscay: BoB) counterpart are due to both biotic and abiotic differences between their ecosystems. Bioenergetic modeling reveals that the slower growth rate of Mediterranean hake favors the MeHg bioaccumulation in the fish muscle and explains most of the difference between GOL and BoB hake populations. In addition, the waters of the Mediterranean hake habitat favor a higher MeHg exposition, due to the upper position of the thermohalocline, where MeHg is formed. Furthermore, we show that, within the Mediterranean hake population, a major increase in the biomagnification power (the slope of the relationships between logMeHg and δ(15)N), from 0.36 up to 1.12, occurs when individuals enter adulthood, resulting from the combined effects of lowering growth rate and change in feeding habits. Finally, δ(15)N normalized Hg concentrations indicate that the highest Hg concentrations are for hake from the shelf edge and the lowest are for hake from the Rhône prodelta area, suggesting a lower Hg bioavailability in inshore environments, consistent with MeHg distributions in water, sediment, and preys.

Preventing the collapse of the Baltic cod stock through an ecosystem-based management approach.

Worldwide a number of fish stocks have collapsed because of overfishing and climate-induced ecosystem changes. Developing ecosystem-based fisheries management (EBFM) to prevent these catastrophic events in the future requires ecological models incorporating both internal food-web dynamics and external drivers such as fishing and climate. Using a stochastic food-web model for a large marine ecosystem (i.e., the Baltic Sea) hosting a commercially important cod stock, we were able to reconstruct the history of the stock. Moreover we demonstrate that in hindsight the collapse could only have been avoidable by adapting fishing pressure to environmental conditions and food-web interactions. The modeling approach presented here represents a significant advance for EBFM, the application of which is important for sustainable resource management in the future.

The role of molecular size in antioxidant activity of peptide fractions from Pacific hake (Merluccius productus) hydrolysates.

The antioxidative properties of Pacific hake hydrolysates and their peptidic fractions varying in molecular size were assessed. Hydrolysates produced by different proteases (Alcalase, bromelain, Flavourzyme, Protamex, Protease A"Amano"2, Protease N"Amano"K, Protin SD NY10, Umamizyme-K, Validase BNP-L, Validase FPexo) generally possessed good metal ion chelating (33-73% at 3mg/ml), DPPH radical scavenging (18-30% at 1mg/ml), ferric ion reducing power (abs700nm 0.36-0.86 at 3 mg/ml) and ABTS radical scavenging (47-85% at 0.067 mg/ml) activity, as well as a good capability to suppress lipid peroxidation in a linoleic acid model system. Peptide size (<1.4 kDa) was important for ABTS radical scavenging activity, whereas specific peptide composition (which depended on the particular protease used) was the governing factor for effective lipid peroxidation. Validase BNP-L was the most promising enzyme for producing Pacific hake hydrolysates with good antioxidative activity in various assays and similar effectiveness as the synthetic antioxidant BHT to inhibit lipid peroxidation.

Endoparasite fauna of five Gadiformes fish species from the coast of Chile: host ecology versus phylogeny.

The aims of the present study were to compare, using multivariate analyses, the degree of similarity of the endoparasite fauna of five fish species belonging to the order Gadiformes: Merluccius gayi, Merluccius australis, Macruronus magellanicus (Gadoidei) and Micromesistius australis and Nezumia pulchella (Macrouroidei), from the southern and central Chilean coast, and to evaluate whether the composition of the endoparasite fauna was determined by phylogenetic or ecological relationships. We employed our database of Merluccius australis, M. magellanicus and Micromesistius australis, which was complemented with published information for M. magellanicus, Merluccius australis, Micromesistius australis, M. gayi and N. pulchella. A higher number of endoparasite species was recorded for Merluccius australis, Micromesistius australis and M. magellanicus, namely Anisakis sp. and Hepatoxylon trichiuri, which is the most prevalent parasite among these hosts. Aporocotyle wilhelmi and Hysterothylacium sp. were detected only in M. gayi, whereas Lepidapedon sp. was found exclusively in N. pulchella. These results suggest that fish ecology rather than host phylogeny was the most important factor for the determination of similarity in parasite composition. This result could be explained by the similar trophic patterns of hosts and by the predominance of generalist larval species among these fish parasite communities.