Male Atlantic Cod Research Articles

Integrative omics-analysis of lipid metabolism regulation by peroxisome proliferator-activated receptor a and b agonists in male Atlantic cod.

Lipid metabolism is essential in maintaining energy homeostasis in multicellular organisms. In vertebrates, the peroxisome proliferator-activated receptors (PPARs, NR1C) regulate the expression of many genes involved in these processes. Atlantic cod (Gadus morhua) is an important fish species in the North Atlantic ecosystem and in human nutrition, with a highly fatty liver. Here we study the involvement of Atlantic cod Ppar a and b subtypes in systemic regulation of lipid metabolism using two model agonists after in vivo exposure. WY-14,643, a specific PPARA ligand in mammals, activated cod Ppara1 and Ppara2 in vitro. In vivo, WY-14,643 caused a shift in lipid transport both at transcriptional and translational level in cod. However, WY-14,643 induced fewer genes in the fatty acid beta-oxidation pathway compared to that observed in rodents. Although GW501516 serves as a specific PPARB/D ligand in mammals, this compound activated cod Ppara1 and Ppara2 as well as Pparb in vitro. In vivo, it further induced transcription of Ppar target genes and caused changes in lipid composition of liver and plasma. The integrative approach provide a foundation for understanding how Ppars are engaged in regulating lipid metabolism in Atlantic cod physiology. We have shown that WY-14,643 and GW501516 activate Atlantic cod Ppara and Pparb, affect genes in lipid metabolism pathways, and induce changes in the lipid composition in plasma and liver microsomal membranes. Particularly, the combined transcriptomic, proteomics and lipidomics analyses revealed that effects of WY-14,643 on lipid metabolism are similar to what is known in mammalian studies, suggesting conservation of Ppara functions in mediating lipid metabolic processes in fish. The alterations in the lipid profiles observed after Ppar agonist exposure suggest that other chemicals with similar Ppar receptor affinities may cause disturbances in the lipid regulation of fish. Model organism: Atlantic cod (Gadus morhua). LSID: urn:lsid:zoobank.org:act:389BE401-2718-4CF2-BBAE-2E13A97A5E7B. COL Identifier: 6K72F.

A Nanopore Based Chromosome-Level Assembly Representing Atlantic Cod from the Celtic Sea.

Currently available genome assemblies for Atlantic cod (Gadus morhua) have been constructed from fish belonging to the Northeast Arctic Cod (NEAC) population; a migratory population feeding in the Barents Sea. These assemblies have been crucial for the development of genetic markers which have been used to study population differentiation and adaptive evolution in Atlantic cod, pinpointing four discrete islands of genomic divergence located on linkage groups 1, 2, 7 and 12. In this paper, we present a high-quality reference genome from a male Atlantic cod representing a southern population inhabiting the Celtic sea. The genome assembly (gadMor_Celtic) was produced from long-read nanopore data and has a combined contig length of 686 Mb with an N50 of 10 Mb. Integrating contigs with genetic linkage mapping information enabled us to construct 23 chromosome sequences which mapped with high confidence to the latest NEAC population assembly (gadMor3) and allowed us to characterize, to an extent not previously reported large chromosomal inversions on linkage groups 1, 2, 7 and 12. In most cases, inversion breakpoints could be located within single nanopore contigs. Our results suggest the presence of inversions in Celtic cod on linkage groups 6, 11 and 21, although these remain to be confirmed. Further, we identified a specific repetitive element that is relatively enriched at predicted centromeric regions. Our gadMor_Celtic assembly provides a resource representing a ‘southern’ cod population which is complementary to the existing ‘northern’ population based genome assemblies and represents the first step toward developing pan-genomic resources for Atlantic cod.

Spawning success of cultured and wild male Atlantic cod Gadus morhua does not differ during paired contests

Spawning success of cultured and wild male Atlantic cod Gadus morhua does not differ during paired contests

Effects of oil pollution and persistent organic pollutants (POPs) on glycerophospholipids in liver and brain of male Atlantic cod (Gadus morhua)

Fish in the North Sea are exposed to relatively high levels of halogenated compounds in addition to the pollutants released by oil production activities. In this study male Atlantic cod (Gadus morhua) were orally exposed to environmental realistic levels (low and high) of weathered crude oil and/or a mixture of POPs for 4weeks. Lipid composition in brain and in liver extracts were analysed in order to assess the effects of the various pollutants on membrane lipid composition and fatty acid profiles. Transcriptional effects in the liver were studied by microarray and quantitative real-time RT-PCR. Chemical analyses confirmed uptake of polychlorinated biphenyls (PCBs) and chlorinated pesticides, polybrominated diphenyl ethers (PBDEs) and perfluorooctanesulfonate (PFOS) in the liver and excretion of metabolites of polyaromatic hydrocarbons (PAHs) in the bile. Treatment with POPs and/or crude oil did not induce significant changes in lipid composition in cod liver. Only a few minor changes were observed in the fatty acid profile of the brain and the lipid classes in the liver. The hypothesis that pollution from oil or POPs at environmental realistic levels alters the lipid composition in marine fish was therefore not confirmed in this study. However, the transcriptional data suggest that the fish were affected by the treatment at the mRNA level. This study suggests that a combination of oil and POPs induce the CYP1a detoxification system and gives an increase in the metabolism and clearing rate of PAHs and POPs, but with no effects on membrane lipids in male Atlantic cod.

Competitive spawning success and fertility of triploid male Atlantic cod Gadus morhua

Farmed Atlantic cod Gadus morhua have been hypothesized to pose a risk to the natural environment through escape of fish or release of their gametes from sea cages. The use of sterile triploids has been suggested as a way to prevent spawning of farmed fish, whether escaped from their cages or still contained within them. This laboratory study examined the reproductive potential of triploid male Atlantic cod, both in vivo and in vitro. We demonstrated that triploid males in com- petitive, size-matched mating with diploid males were successful at siring young. Spermatozoa pro- duced by triploid males were larger than those of diploids, but did not differ in swimming velocity or ability to fertilize eggs. Hatch and larval survival rates, however, were reduced for progeny of triploid males. These diagnostic characteristics of aneuploidy suggest that although farmed triploid male cod may compete successfully with wild diploids for spawning access to wild females, their offspring will not survive.

Shifting reproductive success in a shoal of Atlantic Cod, Gadus morhua L.

Individual and temporal variability in the spawning behaviour of Atlantic Cod (Gadus morhua L.) was examined by studying wild and reared individuals from the same putative population in a common spawning arena. The number of eggs fertilized per male was best explained by the number of aggressive interactions initiated by each male. A strong skew in male reproductive success and a temporal shift in male fertilization success were also observed. The latter co-occurred with an apparent similar temporal shift in the reproductive behaviour of the individual males. We hypothesize that energetic costs associated with reproduction, potentially mediated by sperm depletion in dominant individuals, may be responsible for temporal shifts in mating behaviour and reproductive success of male Atlantic Cod. We suggest that this hypothesis merits further study.

A link between sound producing musculature and mating success in Atlantic cod

Individual variability in the mating success of male Atlantic cod Gadus morhua was quantified within an aggregation (n= 59) breeding undisturbed in a large (684 m3) mesocosm tank. Observational and morphometric data were examined to assess the degree to which this mating variation could be explained by aspects of morphology, condition and spawning behaviour. The number of ventral mounts initiated (i.e. mating success) was highly variable; most mounts were initiated by a very small percentage of available males. The significant correlate of male mating success was mass of the sound producing musculature, i.e. drumming muscles. Neither body size, condition, pelvic and median fin morphology nor aggression influenced the number of ventral mounts initiated by a male. The present study suggests a possible link between sound production and mating success in Atlantic cod.

Effect of temperature and food availability on reproductive investment of first-time spawning male Atlantic cod, Gadus morhua

Abstract This study demonstrates how temperature and food availability affect growth, maturation, and sperm production in first-time spawning male cod in captivity. Cod, prior to the onset of maturation, were held under four different varying temperature and feeding regimes between November 2002 and March 2003. Lower food availability resulted in poor growth and body condition. Decreasing temperature partly led to slower growth in fish that matured during the experiment. Low temperature resulted in lesser proportions of mature fish relative to the higher temperature treatments. Higher temperature and food availability resulted in higher sperm production (testicular weight and gonadosomatic index). Our findings suggest that variation in food availability would mainly affect the growth and condition and the level of gamete production whilst variation in temperature would affect the proportion of males that mature. These results are contrasted with similar data for female cod.

The Effect of Photoperiod on Sexual Maturation, Appetite and Growth in Wild Atlantic Cod (Gadus morhua L.)

An experiment was conducted to examine (a) the effects of photoperiod on timing of sexual maturation (b) the relationship between plasma steroid levels, appetite and growth in male and female Atlantic cod (Gadus morhua L.). Wild caught Norwegian coastal cod were subjected to either a 6L/18D photoperiod typical of January at 60° N-(Short day group) or a simulated natural photoperiod (Normal day group) from June 2000 until spawning started. Appetite of individual fish were measured twice weekly, while weight, length and plasma levels of the sex steroids testosterone (T), 11 keto-testosterone (11-KT) and estradiol-17β (E2) were monitored bimonthly. Cod in the Short day group matured 3 months ahead of the cod in the Normal day group and started spawning in early November. Appetite decreased in both sexes 2–3 months prior to spawning in both groups, but this reduction was stronger among males. In both sexes, length growth was reduced concurrently with the appetite loss. Overall, females had significantly higher somatic growth, put relatively less energy into length growth and had developed larger livers compared to males at the time of spawning in the Short day group. Plasma steroid levels increased in both groups throughout the experiment, reaching peak levels of ca 10 ng ml−1 (T) and 15–20 ng ml−1 (11-KT) in males, and 1.5–2 ng ml−1 (T) and 12–18 ng ml−1 (E2) in females at the onset of spawning. Steroid levels increased more rapidly among Short day cod verifying the earlier onset of maturation. These results confirm that photoperiod is a major cue to maturation in cod and imply that the high cost of spawning for females incur differences in appetite between the sexes.

Effects of alkylphenols on CYP1A and CYP3A expression in first spawning Atlantic cod ( Gadus morhua)

Alkylphenols are continuously released into the ocean as a result of offshore oil production. Alkylphenols, including 4- tert-butylphenol (C 4), 4 n-pentylphenol (C 5), 4 n-hexylphenol (C 6), and 4 n-heptylphenol (C 7), up to 237 ppb concentrations, have been detected in produced water from oil platforms. Previous studies have shown that alkylphenols induce vitellogenesis in fish. Atlantic cod ( Gadus morhua) of both sexes were force-fed with various doses ranging between 0.02 and 80 ppm of a mixture of alkylphenols (C 4:C 5:C 6:C 7 ratio 1:1:1:1) or 5 ppm 17β-estradiol. We investigated effects on hepatic CYP1A and CYP3A protein expression in protein blots, using antibodies against scup ( Stenotomus chrysops) CYP1A1 and rainbow trout ( Oncorhynchus mykiss) CYP3A. There was a sexually dimorphic expression of CYP1A and CYP3A protein levels, with females expressing higher levels than males. Treatment of male Atlantic cod with 17β-estradiol resulted in increased CYP1A and CYP3A protein levels. Exposure to alkylphenols resulted in a dose-dependent increase of CYP1A and CYP3A protein expression in males, but not in females. However, this increase of CYP1A protein levels was not reflected on the CYP1A-mediated ethoxyresorufin- O-deethylase (EROD) activity, implying that alkylphenols inhibited the CYP1A enzyme activity in vivo. In vitro inhibition studies with pooled liver microsomes from Atlantic cod confirmed that the alkylphenols mixture efficiently inhibited the CYP1A activity (IC 50=10 μM), although the inhibitory effect of each individual alkylphenol varied. The IC 50 values for each individual alkylphenol on the CYP1A activity were, in a descending order of magnitude: [C 7>C 6>C 5⪢C 4], ranging from 12 to 300 μM with decreased length of the 4-alkyl chain. The effect of alkylphenols on the CYP3A activity in vitro in liver microsomes also was investigated, using the fluorescent 7-benzyloxy-4-[trifluoromethyl]-coumarin (BFC) as a diagnostic CYP3A substrate. The alkylphenol mixture inhibited CYP3A activity with IC 50 value at 100 μM. The IC 50 values for each individual alkylphenol on CYP3A activity were, in a descending order of magnitude: [C 5>C 6>C 7>C 4], ranging between 60 and 250 μM. Taken together, our results show that the alkylphenol mixture and 17β-estradiol resulted in elevated hepatic CYP1A and CYP3A expression in male Atlantic cod. The alkylphenol mixture strongly inhibited CYP1A activities, whereas it weakly inhibited CYP3A activity in Atlantic cod liver microsomes in vitro. In addition, 17β-estradiol was a weak inhibitor of CYP3A activity (IC 50=75 μM) and did not notably inhibit the CYP1A activity in vitro.

Gonadal development and associated changes in liver size and sexual steroids during the reproductive cycle of captive male and female Atlantic cod ( Gadus morhua L.)

Gametogenesis in female and male Atlantic cod ( Gadus morhua L.) was investigated by sampling blood plasma and gonadal tissue from 19 to 33-month-old fish. The reproductive cycles of both female and male Atlantic cod are characterized by distinct annual variations in gonadal size and developmental stage and these are associated with changes in sex steroids and liver size. I H did not change during early gonadal development, but both spent females and males had lower I H than late maturing females and spermiating males, respectively. In females I G was correlated to plasma E2 levels and they were highest in spawning females. The lowest levels during the reproductive cycle were observed in spent females. Plasma T levels were low throughout ovarian development, and were at a minimum in spent females. 11-ketotestosterone in plasma of males increased rapidly during spermiation, while T increased at earlier testicular stages and reached maximum during spermiation. High plasma levels of steroids in male and female cod during spawning serve to promote further development and growth of less advanced stages of germ cells.

Male reproductive success and body size in Atlantic cod Gadus morhua L.

Body size is often positively associated with mating success in fish. However, mating success may not accurately represent reproductive success (number of progeny produced). We tested the null hypothesis that reproductive success in male Atlantic cod, Gadus morhua, is not directly proportional to body size. Two allozyme loci and one minisatellite locus were used to estimate the proportion of larvae sired by pairs of males differing in body size and spawning with one female in each of eight tanks during an entire spawning season. Genotypes of progeny from 51 spawning events (egg batches) showed that both males fertilised eggs in each tank. Multiple paternity of larvae occurred in 35 batches. The estimated proportion of larvae sired by each male varied randomly among egg batches within tanks. Male size, condition factor, and total or relative body-weight loss over the season were not correlated with the estimated proportion of larvae sired by each male during the spawning season. Relative activity of males wasmarginally associated with male reproductive success, with more active males siring a larger proportion of larvae. Male reproductive success was affected by female size, with males much larger (> 25% total length) than females siring a smaller proportion of larvae.

The reproductive cycle of male Atlantic cod (Gadus morhua L.) from Placentia Bay, Newfoundland

The timing of the reproductive cycle of male Atlantic cod (Gadus morhua L.) from Placentia Bay, Newfoundland, was determined from histological gonad samples collected throughout the year. Cycles in gonad mass, whole mass, and somatic mass indices were also determined. Results were consistent with a spring spawning population, with males having testes filled with spermatozoa as early as January. There was a short resting period following spermiation, during which residual sperm was resorbed, followed by rapid development so that some sperm was again evident in the testes as early as November. At first, the presence of spermatozoa was accompanied by cells in all other stages of development, but by spermiation the testes were filled mostly with spermatozoa. Gonad size was largest in April, smallest in October, and increased steeply again in November. Energy for gonad growth came from food intake, as well as liver lipid stores. Gonad development was, for the most part, finished prior to the winter reduction in feeding intensity.

The reproductive cycle of male Atlantic cod (<i>Gadus morhua</i> L.) from Placentia Bay, Newfoundland

The timing of the reproductive cycle of male Atlantic cod (Gadus morhua L.) from Placentia Bay, Newfoundland, was determined from histological gonad samples collected throughout the year. Cycles in gonad mass, whole mass, and somatic mass indices were also determined. Results were consistent with a spring spawning population, with males having testes filled with spermatozoa as early as January. There was a short resting period following spermiation, during which residual sperm was resorbed, followed by rapid development so that some sperm was again evident in the testes as early as November. At first, the presence of spermatozoa was accompanied by cells in all other stages of development, but by spermiation the testes were filled mostly with spermatozoa. Gonad size was largest in April, smallest in October, and increased steeply again in November. Energy for gonad growth came from food intake, as well as liver lipid stores. Gonad development was, for the most part, finished prior to the winter reduction i...

Effects of Long-Term Temperature Acclimation on Thyroid Hormone Deiodinase Function, Plasma Thyroid Hormone Levels, Growth, and Reproductive Status of Male Atlantic Cod,Gadus morhua

The recent collapse of the Northwestern Atlantic cod fisheries has coincided with a cooling of water temperatures. During this time the condition factor of cod has been poor. The objective of the present study was to determine the effects of long-term temperature acclimation on growth reproduction and thyroid function in laboratory held Atlantic cod (Gadus morhua). One of the key parameters used to assess thyroid function is the peripheral metabolism ofl-thyroxine (T4) by microsomal deiodinase enzymes. Deiodinase function has not been described for gadid fish. T4outer-ring deiodinating activity (apparentKm1–2 nM) was confined primarily to liver. Its properties resembled those for hepatic T4ORD activity of other teleosts and the mammalian type II deiodinase. The T4ORD activity of cod liver exceeded that of salmonids and could explain the high plasma T3levels (10–18 ng/ml), which were 2–5 times greater than T4levels. T4and T3inner-ring deiodination was confined mainly to brain. In order to determine the effects of long-term temperature acclimation on cod, somatic growth, reproduction, and thyroidal status were assessed monthly in 400–900-g satiation-fed male Atlantic cod captured in June from the St. Lawrence Estuary and then acclimated from August to the following June under a natural photoperiod at 2–4°C (LT) or 6–10°C (HT). Reproductive status was determined from the gonadosomatic index (GSI), plasma testosterone (T) and 11-ketotestosterone (11-KT) levels, and the appearance of milt; thyroidal status was determined from plasma T4and 3,5,3′-triiodo-l-thyronine (T3) levels and hepatic T4ORD activity to produce biologically active T3. Testis maturation (high levels of T and 11-KT, and milt release) occurred in April and May and was uninfluenced by acclimation temperature. LT cod grew more slowly than HT cod. Differences in body weight were particularly evident from December to February. In conclusion, (i) cod possess outer- and inner-ring deiodinase activities, predominating respectively in liver and brain, and with properties resembling those of other teleosts, (ii) T4ORD activity of liver is unusually high and may account for the high plasma T3levels in this species, (iii) T4ORD activity tends to increase during periods of increased somatic growth, and (iv) chronic acclimation of male cod to 2–4°C, as opposed to 6–10°C, decreases somatic growth but does alter circulating levels of thyroid hormones and androgens and it does not change the time of sexual maturation.