Role of temperature on lipid/fatty acid composition in Pacific cod (Gadus macrocephalus) eggs and unfed larvae

During early development, oviparous fish species must use finite lipid and fatty acid (FA) reserves for both catabolism and structural components. In cold environments, developing fish have the additional constraint of maintaining membrane fluidity for metabolic efficiency (homeoviscous adaptation), resulting in further demand on lower melting point FAs like n-3 polyunsaturated fatty acids (PUFAs). To examine whether marine fish embryos physiologically adapt to changing temperature environments, we incubated Pacific cod (Gadus macrocephalus) eggs at 5 temperatures (0, 2, 4, 6, and 8 °C) in the laboratory and sampled them repeatedly during development to measure changes in lipid/FA composition. Pacific cod embryos increased n-3 PUFA content during the egg stage in all temperature treatments, with the possible exception of 0 °C, where poor survival and hatch success limited our ability for continued sampling. At the beginning of the hatch cycle, free-swimming embryos shifted from lipogenesis to lipid catabolism. The rates of lipogenesis and catabolism were temperature dependent, and the distinct increase in unsaturated fatty acids at temperatures <8 °C was consistent with homeoviscous adaptation theory. However, with the possible exception of embryos at 0 °C, the relative amounts of essential fatty acids (e.g., EPA, DHA, AA) were conserved in a similar manner across incubation temperatures. Collectively, these data suggest Pacific cod are capable of homeoviscous adaptation but cannot tolerate temperatures approaching 0 °C despite their possible ability to biosynthesize PUFAs from other energetic sources

Effect of temperature and tissue type on fatty acid signatures of two species of North Pacific juvenile gadids: A laboratory feeding study

The utility of the fatty acid biomarker (FAB) approach in fisheries ecology is limited by our understanding of how biotic and abiotic factors determine dietary markers in fish tissues. An 8-week laboratory experiment was conducted on two species of juvenile gadids (Pacific cod, Gadus macrocephalus and walleye Pollock, Theragra chalcogramma) reared at 3 °C or 9 °C and fed a diet enriched with either oils of marine origin or terrestrial plant origin. Non-linear models were fitted to investigate how tissue type and temperature mediated the proportion of FABs in fish. Across temperatures, fatty acid (FA) profiles were similar for both species of gadids. FAs also showed high temporal sensitivity across temperatures, and were evident in fish after only one week of feeding. Pacific cod held at 9 °C and fed a terrestrial plant oil (TPO) enriched diet had significantly higher C₁₈ polyunsaturated FAs (PUFAs) in their liver than cod held at 3 °C after one week, but this temperature effect diminished as tissues reached equilibrium with their diet. C₁₈ PUFAs were significantly higher in liver than in muscle.Differential proportions of C₁₈ PUFAs among tissues provide temporal patterns that may help with disentangling the timing of offshore– inshore nursery migrations in juvenile fish. Calibration coefficients were determined to explain the relationship between FAs in the diet and FAs in fish tissues. These coefficients will support future development of quantitative estimates of diet in juvenile low-fat fish.Keywords: Juvenile, Cod, Pollock, Fatty acid, Biomarker, Temperatur

Temperature-dependent growth and behavior of juvenile Arctic cod (Boreogadus saida) and co-occurring North Pacific gadids

The thermal sensitivity of Arctic fish species is poorly understood, yet such data are a critical component of forecasting and understanding ecosystem impacts of climate change. In this study, we experimentally measured temperature-dependent growth and routine swim activity in the juvenile stage of two Arctic gadids (Arctic cod, Boreogadus saida and saffron cod, Eleginus gracilis) and two North Pacific gadids (walleye pollock, Gadus chalcogrammus and Pacific cod, Gadus macrocephalus) over a 6-week growth period across five temperatures (0, 5, 9, 16 and 20°C). Arctic cod demonstrated a cold-water, stenothermic response in that there was relatively high growth at 0°C (0.73 % day⁻¹), near-maximal growth at 5°C (1.35 % day⁻¹) and negative impacts on activity, growth and survival at 16 °C. In contrast, saffron cod demonstrated a warmer-water, eurythermic response, and temperature had a positive effect on growth and condition beyond 16°C. However, despite these distinct thermal responses, walleye pollock and Pacific cod grew 2–3 times faster than Arctic gadids across a relatively broad temperature range above 5°C. These results, coupled with possible northward expansion by both Pacific cod and walleye pollock, suggest Arctic cod are highly vulnerable to continued climate change in the Arctic, especially in coastal areas of the Beaufort and Chukchi Seas where temperatures already exceed 14°C in the summer growth period.This is the publisher’s final pdf. The article is copyrighted by the US Government and published by Springer. It can be found at: http://link.springer.com/journal/300Keywords: Climate change, Saffron cod, Walleye pollock, Thermal sensitivity, Pacific cod, Biogeograph

Total Lipids, Lipid Classes, and Fatty Acids of Newly Settled Red King Crab (Paralithodes camtschaticus): Comparison of hatchery-cultured and wild crabs

Little is known about the nutrition or lipid metabolism of cold-water crabs, particularly in the North Pacific. We undertook a 2-part study to understand more completely the energetics and nutritional requirements of juvenile red king crab (RKC; Paralithodes canusehaticus). First, we investigated changes in proximate composition, total lipids (TLs), lipid classes, and fatty acids (FAs) throughout a molt cycle (C4-C5). Trends in lipid parameters were described by a 3-pari, piecewise linear regression with 3 distinct stages: (I) a postmolt phase (similar to 0-7 days), (2) an intramolt stage (similar to 7-24 days), and (3) a premolt stage (similar to 24-33 days). Significant intramolt differences in TLs indicated that caution should be taken when comparing crabs of unknown molt stage in future aquaculture and ecological experiments. However, little variability was found in the proportional FA composition of crabs, indicating that the intramolt stage has little effect on the interpretation of FA biomarkers. During a second investigation, we examined differences in lipid classes and FAs from cultured and wild RKC. We found significantly higher proportions of the essential fatty acids (EFAs) 20:5n-3 (EPA) and 20:4n-6 (AA) in wild crabs compared with cultured animals at the same stage. Furthermore, higher proportions of bacterial markers and lower proportions of zooplankton FA markers were found in wild than in hatchery-reared crabs. Here, we provide the first baseline data for future dietary studies on juvenile cold-water crabs. We suggest that an initial EFA ratio for DHA:EPA:AA of 5:8:1 could be used as a starting point for controlled dietary studies on the effect of EFAs on juvenile growth, molt success, and survival.Keywords: Lipids, Nutrition, Red king crab, Paralithodes camtschaticus, Fatty acids, Mol

The circumpolar impacts of climate change and anthropogenic stressors on Arctic cod (Boreogadus saida) and its ecosystem

Arctic cod biomass are predicted. In most Arctic seas, the relative abundance of Arctic cod within the fish community will likely fluctuate in accordance with cold and warm periods. A reduced abundance of Arctic cod will negatively affect the abundance, distribution, and physiological condition of certain predators, whereas some predators will successfully adapt to a more boreal diet. Regional management measures that recognize thecritical roleof Arcticcod arerequiredtoensure that increased anthropogenic activities do not exacerbate the impacts of climate change on Arctic marine ecosystems. Ultimately, the mitigation of habitat loss for Arctic cod will only be achieved through a global reduction in carbon emissions

Lipid biomarkers and essential fatty acids in trophic ecology and nutrition of age-0 gadids

Over the last 30 years, lipids have been used to study patterns of energy flow and food web dynamics in cold and temperate marine ecosystems. I used fatty acids (FAs) and lipid classes to better understand the early survival, nutrition, habitat use and growth of age-0 Atlantic and Pacific gadids, both through laboratory and field approaches. Firstly, I used lipids to examine condition of age-0 juvenile Atlantic cod (Gadus morhua) as they settled in eelgrass (Zostera marina) nursery habitat. Cod reduced lipids per wet weight at the time of settlement, indicating that energy was directed towards rapid growth rather than storage for overwintering. Secondly, I used both FA biomarkers (FABMs) and compound specific carbon isotopes of FAs to show that increased terrestrial carbon entered the diet of juvenile cod during settlement. Higher dietary short chain polyunsaturated FAs (PUFA), coupled with low proportions of dietary essential FAs (EFAs) in the nearshore foodweb, indicated that the functional significance of eelgrass was refuge, and not elevated nutritional food quality. Thirdly, I conducted a laboratory experiment on the nutritional requirements of Pacific cod (Gadus macrocephalus) larvae to compare with literature values for Atlantic species. This comparative approach indicated that trends in larval nutrition could not be generalized across the family Gadidae. Pacific cod larvae grew fastest with diets containing high levels of n-3 PUFA, similarly to Atlantic species. Unlike Atlantic cod, however, Pacific cod larvae did not show elevated growth and survival with higher dietary proportions of DHA (22:6n-3) relative to EPA (20:5n-3). Fourthly, I investigated the rate of uptake of two C₁₈ PUFAs in tissues of two species of Pacific juvenile gadids (Pacific cod, Gadus macrocephalus and walleye Pollock, Theragra chalcogramma). I examined how both biotic and abiotic factors influenced the rate of uptake in liver, flesh and heart tissues. C₁₈ PUFAs showed high temporal sensitivity, and were evident in fish tissues after only one week of feeding. The differential uptake of these FABMs among tissues could represent a new tool to disentangle timing of offshore-inshore nursery migrations in juvenile fish. Throughout, this thesis I have shown that lipid classes, FABMs and EFAs can be successfully used to indicate critical trophic events during the early life history of gadid fish

Lipid nutrition during early development of yellowtail flounder (Limanda ferruginea)

Yellowtail flounder (Limanda ferruginea) is a candidate species for cold-water aquaculture development in Atlantic Canada. However, mal-pigmentation and high larval mortality are still major obstacles to the successful culture of this species. Starvation due to inadequate nutrition is believed to be a major cause of this mortality. In particular, lipid nutrition has shown significant effects on the early development in a number of marine species. This study is the first examination of the dietary lipid requirements of yellowtail flounder larvae. -- Specifically, marine fish require the dietary polyunsaturated fatty acids docosahexaenoic acid (DHA, 22:6n-3), eicosapentaenoic acid (EPA, 20:5n-3) and arachidonic acid (AA, 20:4n-6) for normal growth and development. Consequently, in Chapter Two (Part A) an experiment was designed to study the role of dietary ratios of these fatty acids on the early growth, survival, lipid composition, and pigmentation of yellowtail flounder. Rotifers were enriched with experimental emulsions with high concentrations of DHA, DHA+EPA, or DHA+AA, or with a control (no DHA, EPA, or AA) emulsion. After four weeks, larvae fed the high DHA diet were significantly larger (9.7 ± 0.2 mm, p<0.05) and had higher survival (22.1 ± 0.4%), while larvae fed the control diet were significantly smaller (7.3 ± 0.2 mm, p<0.05) and showed lower survival (5.2 ± 1.9%). Larval lipid class and fatty acid profiles showed significant differences (p<0.05), with fatty acids reflecting dietary levels in the high PUFA diets. The incidence of mal-pigmentation was higher in the high DHA+AA diet (92%) than in all other treatments (<64%). It was concluded that yellowtail larvae require diets that are highly enriched with DHA while elevated dietary AA exerts negative effects on larval pigmentation. -- In Chapter Two (Part B) I examined the changes in growth and lipid composition that occurred when larvae of differing nutritional status were fed one diet of enriched Artemia. Significant changes in larval lipid class and fatty acid composition were observed after just two weeks of feeding on enriched Anemia. Control larvae showed a period of 'lipid recovery' while animals fed all other treatments showed a period of decreased lipid unsaturation. However, all larvae demonstrated a dramatic increase in size despite decreased dietary highly unsaturated fatty acids (HUFA). Therefore, it was concluded that high levels of HUFA may not be as essential during later larval development as during initial stages of first-feeding. -- In Chapter Three the lipid composition of mal-pigmented (MP) and normally pigmented (NP) newly settled yellowtail flounder were compared in order to elucidate a possible connection between lipids and pigmentation development. NP fish were found to be significantly larger than MP fish (p=0.04) at the time of 100% settlement. Higher relative amounts of triacylglycerols were found in NP fish (p=0.02) while MP fish had higher relative amounts of phospholipids (p=0.008). NP fish had higher relative amounts of DHA in the polar lipids of the body (p=0.03) and in the total lipids of the eye (p=0.04) than did MP juveniles. These data support previously proposed theories for the importance of DHA in pigmentation development

CopemanLouiseHMSCEffectTemperatureTissueSupplementalMaterial.pdf

The utility of the fatty acid biomarker (FAB) approach in fisheries ecology is limited by our understanding of how biotic and abiotic factors determine dietary markers in fish tissues. An 8-week laboratory experiment was conducted on two species of juvenile gadids (Pacific cod, Gadus macrocephalus and walleye Pollock, Theragra chalcogramma) reared at 3 °C or 9 °C and fed a diet enriched with either oils of marine origin or terrestrial plant origin. Non-linear models were fitted to investigate how tissue type and temperature mediated the proportion of FABs in fish. Across temperatures, fatty acid (FA) profiles were similar for both species of gadids. FAs also showed high temporal sensitivity across temperatures, and were evident in fish after only one week of feeding. Pacific cod held at 9 °C and fed a terrestrial plant oil (TPO) enriched diet had significantly higher C₁₈ polyunsaturated FAs (PUFAs) in their liver than cod held at 3 °C after one week, but this temperature effect diminished as tissues reached equilibrium with their diet. C₁₈ PUFAs were significantly higher in liver than in muscle.Differential proportions of C₁₈ PUFAs among tissues provide temporal patterns that may help with disentangling the timing of offshore– inshore nursery migrations in juvenile fish. Calibration coefficients were determined to explain the relationship between FAs in the diet and FAs in fish tissues. These coefficients will support future development of quantitative estimates of diet in juvenile low-fat fish.Keywords: Biomarker, Cod, Fatty acid, Pollock, Juvenile, Temperatur

Identification of Burrowing Shrimp Food Sources Along an Estuarine Gradient Using Fatty Acid Analysis and Stable Isotope Ratios

Two species of burrowing shrimp occur in high densities in US West Coast estuaries, the ghost shrimp, Neotrypaea californiensis, and the blue mud shrimp, Upogebia pugettensis. Both species of shrimp are considered ecosystem engineers as they bioturbate and irrigate extensive galleries within the sediment. While their burrows comprise a dominant habitat type in west coast estuaries, little is known about these shrimps’ diet and their role in estuarine food webs. The primary goals of this study were to identify major components of burrowing shrimp diets and detect variation in these diets along an estuarine gradient using combined fatty acid (FA) and stable isotope (SI) analyses. Shrimp and potential food sources including eelgrass blades, epiphytes, Ulva, sedimentary particulate organic matter (SPOM), burrow walls, and particulate organic material (POM) were sampled at different locations within Yaquina Bay, Oregon in August 2012. Both SI and FA analyses indicated differences in food resources assimilated by shrimp along the estuarine gradient. SI values showed that diets for U. pugettensis consisted of carbon sources derived primarily from POM and SPOM, while POM and epiphytes were primary carbon sources for N. californiensis. Shrimp from lower estuarine sites had high levels of 16:1ω7 and 20:5ω3 FAs suggesting their diet is enriched with marine diatoms. Shrimp from upriver showed greater proportion of FA associated with dinoflagellates and terrestrial sources as indicated by a high percentage of C18 polyunsaturated FAs (PUFAs). This is the first study to evaluate diets of these two shrimp species using complimentary FA and SI approaches