Survival In Seawater Research Articles

Evolution of Green Plants Accompanied Changes in Light-Harvesting Systems.

Photosynthetic organisms have various pigments enabling them to adapt to various light environments. Green plants are divided into two groups: streptophytes and chlorophytes. Streptophytes include some freshwater green algae and land plants, while chlorophytes comprise the other freshwater green algae and seawater green algae. The environmental conditions driving the divergence of green plants into these two groups and the changes in photosynthetic properties accompanying their evolution remain unknown. Here, we separated the core antennae of PSI and the peripheral antennae [light-harvesting complexes (LHCs)] in green plants by green-native gel electrophoresis and determined their pigment compositions. Freshwater green algae and land plants have high Chl a/b ratios, with most Chl b existing in LHCs. In contrast, seawater green algae have low Chl a/b ratios. In addition, Chl b exists not only in LHCs but also in PSI core antennae in these organisms, a situation beneficial for survival in deep seawater, where blue-green light is the dominant light source. Finally, low-energy Chl (red Chl) of PSI was detected in freshwater green algae and land plants, but not in seawater green algae. We thus conclude that the different level of Chl b accumulation in core antennae and differences in PSI red Chl between freshwater and seawater green algae are evolutionary adaptations of these algae to their habitats, especially to high- or low-light environments.

A salt bath will keep you going? Euryhalinity tests and genetic structure of caridean shrimps from Iberian rivers

We assessed the role of euryhalinity and life-history traits on the population genetic structure of the four main caridean shrimp species from the Iberian Peninsula (Atyaephyra desmarestii, Dugastella valentina, Palaemon varians and Palaemon zariquieyi) able to complete their life cycle in freshwater/oligohaline habitats. Seawater exposure experiments indicated that A. desmarestii, D. valentina and P. zariquieyi are more sensitive to high salinity waters than P. varians and confirm the relationship between osmolality regulation and spatial distribution of species. The limited or no survival in seawater could explain the restricted distributions observed in D. valentina and P. zariquieyi, whereas the current A. desmarestii distribution could be due to either past river dynamics and/or human-mediated water transfers. Conversely, the high tolerance of P. varians to a large salinity range (euryhalinity) could explain its capacity to colonize geographically distant estuaries. In agreement with osmoregulation results, the phylogeography patterns of the cytochrome oxidase 1 (Cox 1) gene fragment revealed significant genetic differentiation among river systems whatever the species considered. Atyidae species presented higher nucleotide diversity levels than Palaemonidae species, while isolation-by-distance patterns were only found for the latter. Our results have important implications for the management and conservation of freshwater species, since the inter-catchment connectivity may affect the speciation processes.

Profiles of circulating insulin-like growth factor-I during smoltification of masu salmon reared under different conditions

We compared profiles of serum insulin-like growth factor (IGF)-I levels during smoltification of masu salmon reared under different environments, hatcheries and growth histories. Masu salmon from the Kenichi River in Hokkaido showed a sharp increase in serum IGF-I from April to May, followed by a peak of gill Na+,K+-ATPase (NKA) activity. Fish at Kumaishi Hatchery had an IGF-I profile similar to that of the river fish, while the increase in gill NKA was lower. At Shimamaki Hatchery, interval feeding during winter appeared to suppress the spring IGF-I peak. At Kumaishi Hatchery, a difference in size during smoltification affected IGF-I levels at release, but the numbers of adults that returned to the release site were not significantly different. In the following year, three release groups differing in winter size and/or spring growth (Large-High, Large-Low and Small-High) were created. Large-High and Small-High fish showed a higher IGF-I peak than Large-Low fish in April, while smolt-to-adult return of Large-High fish was highest. These results suggest that in smolting masu salmon in freshwater, circulating IGF-I level alone is not a predictor of long-term survival in seawater. However, since growth history in freshwater affected the smolt-to-adult return, optimizing rearing conditions is a critical component of hatchery releases for masu salmon.

Coastal talitrids and connectivity between beaches: A behavioural test

Beach-hoppers and sandhoppers in the family Talitridae are strongly linked to the supralittoral environment. They are semi-terrestrial animals and because they are direct developers there is potentially no mobility between populations on adjacent beaches. In the case of coastlines fragmented by natural or artificial structures, the assumed lack of inter-connectivity between beaches may represent a severe threat for the resident populations: in case of impacts, they might not be able to recover and the habitat might not be re-colonised. Unless we consider another possible scenario: the potential connectivity of populations via water currents, from individuals swashed accidentally into the sea. We therefore tested two different species, the sandhopper Notorchestia quadrimana and the beach-hopper Platorchestia smithi for features relevant to dispersal and connectivity among beaches: 1) survival in sea-water; 2) orientation (baseline and scototaxis) in sea-water and; 3) behaviour in a current. Talitrid populations were sampled from a sheltered beach and an exposed beach along the New South Wales coast. On the sheltered beach both species were found, co-occurring within the same distance from the shoreline. On the exposed beach only P. smithi was found, in a dune slack far away from the shoreline. All individuals tested survived 96h in immersion, and when subjected to a current they were clinging on the edge of the flume apparatus for most of the duration of the test. Differences emerged when comparing orientation, with the sharpest precision towards a dark pattern (positive scototaxis) in P. smithi from the sheltered beach and bimodal orientation (partly scototactic and partly sun compass) in N. quadrimana. The behavioural differences observed are likely developed as risk-related: sandhoppers burrow in the substrate and are less exposed to occasional swash, while beach-hoppers living in cast wrack displayed the ability of swimming quickly towards a floating object, increasing the likelihood of being passively carried from one beach to another. Different ecological groups such “sandhoppers” and “beach-hoppers” showed different behavioural patterns. The consideration of behavioural answers to swash risk highlighted the possibility of the connectivity of talitrid populations across fragmented beaches.

Toxicity of forest fire retardant chemicals to stream‐type chinook salmon undergoing parr–smolt transformation

Long-term fire retardants are used to prevent the spread of wildland fires. These products are normally applied by aircraft and are intended specifically for terrestrial application, but fire retardants have entered aquatic habitats by misapplication and/or accidental spills and have resulted in fish mortalities. The authors examined the toxicity of two fire retardant products, PHOS-CHEK 259F and LC-95A, to salmon undergoing parr-smolt transformation. Yearling stream-type chinook salmon at the smolt stage were exposed to eight concentrations of each retardant in freshwater and a no-PHOS-CHEK control for 96 h to determine acute toxicity. Concentrations of the products that caused 50% mortality were 140.5 and 339.8 mg/L for 259F and LC-95A, respectively, and could occur during accidental drops into aquatic habitats. Damage to gill tissues seen in histopathological sections was attributed to fire retardant exposure. Un-ionized ammonia levels, from 259F, were sufficient to cause acute mortality; but additional factors, indicated by increased phagosome prevalence in the gills, might have contributed to mortality during LC-95A exposure. Seawater and disease challenges were performed to determine sublethal effects of product exposures on fish health. Although PHOS-CHEK exposure did not adversely affect chinook salmon's susceptibility to Listonella anguillarum, exposure did significantly reduce seawater survival. Reduced salmon survival resulting from prior fire retardant exposure during their transition from freshwater rearing environments to seawater may decrease the abundance of salmon populations.

Virulence of Fish-Pathogenic bacterium Edwardsiella tarda to Red Sea Bream Pagrus major after Survival in Seawater

Virulence of Fish-Pathogenic bacterium Edwardsiella tarda to Red Sea Bream Pagrus major after Survival in Seawater

Survival and Growth of Juvenile Pacific Lampreys Tagged with Passive Integrated Transponders (PIT) in Freshwater and Seawater

AbstractTagging methods are needed for both adult and juvenile life stages of Pacific lampreys Lampetra tridentata to better understand their biology and factors contributing to their decline. We developed a safe and efficient technique for tagging juvenile Pacific lampreys with passive integrated transponder (PIT) tags. We tested the short‐term survival of PIT‐tagged juvenile lampreys in freshwater at four temperatures (9, 12, 15, and 18°C) and their long‐term growth and survival in seawater. For both experiments there was little to no tag loss, and juvenile lampreys in freshwater showed high survival at all temperatures at 7 d (95–100%) and 14 d (88–100%) posttagging. Prolonged holding (40 d) resulted in significantly lower survival (28–79%) at warmer temperatures (12–18°C). For juvenile lampreys tagged in freshwater and then transitioned to seawater, survival was 97% for tagged fish until day 94, and at the end of 6 months, survival was about 58% for both tagged and control fish. About half of the tagged and control fish that survived in seawater grew, but there was no difference in growth between the two groups. In freshwater, but not in seawater, most fish that died had an aquatic fungal infection. In both experiments, survival increased with increasing fish length at tagging. Our results indicate that tags similar in size to a 9‐mm PIT tag are a feasible option for tagging metamorphosed juvenile lampreys migrating downstream and that when fungal infections are mitigated—as in seawater—long‐term (at least 6 months) survival of tagged juvenile lampreys is high.

Continuous light and elevated temperature can trigger maturation both during and immediately after smoltification in male Atlantic salmon ( Salmo salar)

In the present study, two experiments were performed to examine if manipulation of photoperiod and temperature can trigger sexual maturation in male Atlantic salmon during smoltification and in the first period after smoltification. In experiment 1 (exp. 1), parr (83 g) previously reared under LD12:12 were subjected to LD18:6 or LD24:0 photoperiods at 5, 10 or 16 °C FW for six weeks (01 December to 14 January), and then evaluated for maturity status (GSI) and seawater survival (96 h challenge tests in 35‰ salt water). After the six week period, 47% of the males reared under 16 °C–LD24:0 were maturing (GSI 1.5 ± 0.2%). No maturing males were found in the other groups. Survival in seawater was high (> 92%) in all groups. After the challenge tests, all groups except the one held at 16 °C–LD24:0 were terminated. This group was reared on for two months in seawater (8.9 °C and LD24:0) to verify maturation. There was no mortality during the period in seawater, and the GSI of mature males increased to 7.3 ± 0.5%. In experiment 2 (exp. 2), under-yearling smolts (60 g) previously reared under LD24:0 and natural temperature in fresh water were subjected to LD24:0 and 16 °C seawater or to natural temperature seawater and natural photoperiod (60° N, 5° E, Western Norway) for three months (17 October to 20 January), followed by natural temperature and photoperiod for three months (20 January to 29 April). At termination, 8.3% of the fish in the 16 °C–LD24:0 group were fully mature males (running), while there were no mature males in the group reared under natural conditions. The mature males developed a ‘female mimicry’; their lower jaw lacked the kype (hook) typical of mature male adults, and their skin coloration was dark yellow-greenish. These two experiments demonstrate that a combination of elevated temperature and continuous light can trigger maturation both during and immediately after smoltification in male Atlantic salmon. The model presented here (exp. 1, 16 °C–LD24:0) can be used to study potential conflicts between maturation and smoltification in male Atlantic salmon. This is also the first report (exp. 2) of fully mature Atlantic salmon in spring (April–May). In practical terms, the present study shows that the use of LD24:0 at elevated water temperatures increases the risk for post-smolt maturation, or ‘jacking’, in male Atlantic salmon.

Comparative seawater performance and deformity prevalence in out-of-season diploid and triploid Atlantic salmon ( Salmo salar) post-smolts

The use of sterile triploid stock in the Atlantic salmon ( Salmo salar, L) farming industry is the only commercially available means to prevent the ecological impact of domesticated escapees. This study compared the seawater (SW) performance and deformity prevalence of diploid and triploid post-smolts from 2 full-sib families produced out-of-season. Triploids completed smoltification 4 weeks earlier and at a significantly higher body-weight. Growth and survival in SW were not significantly affected by ploidy. The incidence of external deformities, dominated by jaw malformation, was ~ 12% in triploids and below 5% in diploids. Vertebral deformities were more prevalent in the fastest growing triploid family only. Heart morphometry differed between ploidies which may relate to a higher cardiac workload in triploids. No clear alteration of the gill apparatus was detected. The most significant detrimental effect of triploidy was on the rate and severity of cataract that were observed from August onward (50% and 92% of diploids and triploids respectively affected after 1-year in SW). At that time, cataracts were diagnosed by histological examinations as irreversible with a probable osmotic origin which could arise from factors such as water quality, nutritional deficiencies or thermal variations. This study warrants further research aiming at adapting rearing practices to the needs of triploid stocks as to improve their performance and welfare.

Smolt Transformation in Two California Steelhead Populations: Effects of Temporal Variability in Growth

AbstractWe tested the effect of temporal patterns in food supply on life history decisions in coastal steelhead Oncorhynchus mykiss irideus from a Central California coastal (CCC) population (Scott Creek) and a Northern California Central Valley (NCCV) population (upper Sacramento River basin). We manipulated growth through feeding experiments conducted from May to the following March using warm (2006 cohort) and cool (2007 cohort) temperature regimes. Survival in seawater challenges just before the time of typical juvenile emigration provided an index of steelhead smolt versus nonsmolt life history pathways. Survival varied significantly with fish size (with larger fish being more likely to survive than smaller fish) and by source population (with CCC steelhead being more likely to survive than NCCV steelhead of the same size). The timing of increased food supply (treatment group) did not significantly affect seawater survival rates in either NCCV or CCC steelhead. For both strains, the eventual survivors of seawater challenges (putative smolts) diverged from the eventual mortalities (putative nonsmolts) in both size and growth rate by June in both years, suggesting that the initial growth advantages were maintained throughout the experiments. A significant divergence in condition factor between smolts and nonsmolts by December matched the expected morphological transition of smolts, which showed faster growth in length than weight compared with nonsmolts. The apparent timing of the decision window, several months before the typical period of smolt emigration, matches the patterns observed for other salmonids. In coastal California, this decision must occur before fish have had the opportunity to take advantage of improved winter–early spring feeding conditions. These results support the role of early growth opportunity in life history decisions and provide insight into the applicability of life history models for managing California steelhead.

Effect of environmental factors on survival and growth of quahog parasite unknown (QPX) in vitro

Quahog parasite unknown (QPX) is a protistan microorganism associated with mass mortalities of hard clams ( Mercenaria mercenaria) along the northeastern coasts of the United States and maritime Canada. Because several studies indicate modulatory effects of prevailing environmental parameters on disease outbreaks, this study tested the effect of major environmental parameters (temperature, salinity and oxygen concentration; individually or combined) on QPX survival in artificial seawater and parasite growth in culture media in vitro. Three QPX isolates from two different geographic locations were compared. Results indicated that in vitro growth of QPX was optimal in standard culture medium at 34 ppt between 20 °C and 23 °C. Additionally, significant differences in temperature optima were observed for geographically distinct QPX isolates ( p < 0.001) confirming previous studies suggesting the existence of different QPX strains (or ecotypes). When tested in seawater, QPX exhibited opposite trends with higher survival at 15 °C and 15 ppt. Results also demonstrated limited survival and growth of QPX under anoxic conditions. Additionally, results showed that the parasite is able to survive extreme temperatures (−12 °C to 32 °C) suggesting that QPX could overcome short periods of extreme conditions in the field. These results contribute to a better understanding of interactions between QPX and its environment, but potential impacts of environmental conditions on QPX disease development need further work as it also involves clam response to these factors.

Buoyancy, salt tolerance and germination of coastal seeds: implications for oceanic hydrochorous dispersal

Many coastal plant species are widely distributed, including several pan-global species. Long-distance dispersal and physiological resilience of diaspores (i.e. the plant dispersal unit encompassing the seed and any additional surrounding or attached tissues at dispersal) to adverse environmental conditions are possible contributors to the presence of species over hundreds of kilometres of coastline. Dispersal by water (hydrochory) may occur in coastal habitats. This study investigated diaspore traits considered important for oceanic hydrochorous dispersal, including morphology, buoyancy and survival in seawater, and germination under saline conditions for 13 species common to Holocene dune communities in Western Australia. Of the diaspores of 13 species dominant in this coastal community, 11 floated in seawater, with 7 having &gt;50% of diaspores buoyant after 14 days and some diaspores remaining buoyant for 70 days. Of the 10 species that germinated, diaspores of 9 survived exposure to seawater for up to 70 days. Germination of physiologically dormant seeds contained within indehiscent woody fruits and physically dormant seeds was least affected by time in seawater. The effects of varying concentrations of NaCl (0–500 mM) on germination differed between species, but most were able to recover and germinate when transferred to non-saline water. Three different patterns of salt response were observed. It appears likely a combination of diaspore traits, rather than a single factor, facilitate oceanic hydrochorous dispersal.

Seawater Survival of Enteromyxum leei (Myxozoa) Evaluated by In Vitro Viability and In Vivo Infectivity Assays

Seawater Survival of Enteromyxum leei (Myxozoa) Evaluated by In Vitro Viability and In Vivo Infectivity Assays

Protective effect of polygoni cuspidati radix and emodin on Vibrio vulnificus cytotoxicity and infection

Vibrio vulnificus, a good model organism of bacterial septicemia, causes fatal septicemia manifesting a fulminating course and a high mortality rate within days. In order to identify new natural substances preventing V. vulnificus infection, a plant library was screened for inhibiting cytotoxicity to host cells by using Trypan blue staining and LDH assay. We found that Polygoni Cuspidati Radix potently suppressed the acute death of HeLa and RAW264.7 cells in a dose dependent manner. Further studies revealed that Polygoni Cuspidati Radix inhibited V. vulnificus growth and survival in HI broth and seawater, respectively. We confirmed that Polygoni Cuspidati Radix contained high level of emodin by thin layer chromatography (TLC). Emodin showed direct antibacterial activity against V. vulnificus. In addition, emodin prevented the morphologic damages and acute death of HeLa cells caused from V. vulnificus. The safety of Polygoni Cuspidati Radix and emodin to host cells was confirmed by MTT assay. Polygoni Cuspidati Radix and emodin protected mice from V. vulnificus infection.

Evolutionary patterns of Escherichia coli growth in seawater determined with a Host to Coast Environmental Laboratory Analog

The present study investigated evolution- ary patterns of Escherichia coli growth and survival in transmission through the coastal ecosystem between human host and seawater using a novel 'Host to Coast' Laboratory Analog simulating an 11 d sequence cycling through the pH and temperature conditions of the small intestine, colon, sewer, seawater, human stomach, and back into the small intestine. Although historically E. coli has been assumed to die off rapidly in seawater, a few instances of E. coli growth have been observed in environmental fresh water, soils, and nutrient- enriched tropical seawater, suggesting the potential for evolving greater viability in such environments. This study investigated whether E. coli can evolve increased capacity for growth and survival in seawater through selective exposures to singular abiotic factors such as the high alkalinity or low temperatures approx- imating coastal aquatic conditions, and also whether adaptation to cycling pH can lead to increased growth fitness in a human host. Specialists and generalists were examined to reveal patterns of trade-offs in the multi-stress environment of the Analog. Dramatic increases in fitness revealed in the Host to Coast Ana- log due to evolutionary exposure to alkalinity and cycling pH suggested that these factors are critically important in the evolutionary ecology of E. coli. Evolv- ing the capacity for seawater survival and growth, combined with increased capability to infect human hosts, could facilitate E. coli infection from seawater exposure. Results suggest implications for wastewater management in order to prevent superior strains of pathogenic E. coli from evolving.

Effects of starvation and macroalgae extracts on the survival and growth of quahog parasite unknown (QPX)

Quahog parasite unknown (QPX) is a relatively poorly characterized protistan parasite that causes QPX disease in infected hard clams ( Mercenaria mercenaria). Most prior studies presented descriptive reports of the occurrence and the characteristics of the disease in cultured and wild clams, while several basic aspects of the biology and ecology of the parasite remain obscure. In an attempt to better understand factors affecting the persistence and growth of QPX in marine environment, we investigated the ability of QPX to survive in seawater and the potential role of macroalgae in supporting its growth. An association with macroalgae is particularly relevant because several members of the phylum to which QPX belongs are known to live in association with marine macroalgae and vascular plants. Results indicate that while QPX did not appear to grow in seawater under laboratory conditions, the parasite may be capable of long-term survival in seawater without growth. QPX was able to grow using macroalgae homogenates as a source of nutrients, although extracts from certain macroalgae species significantly inhibited the in vitro growth of QPX. Overall, our results suggest that macroalgae might be an important factor for the survival, growth and spread of QPX in the marine environment.

Molecular ecophysiology of Antarctic notothenioid fishes

The notothenioid fishes of the Southern Ocean surrounding Antarctica are remarkable examples of organismal adaptation to extreme cold. Their evolution since the mid-Miocene in geographical isolation and a chronically cold marine environment has resulted in extreme stenothermality of the extant species. Given the unique thermal history of the notothenioids, one may ask what traits have been gained, and conversely, what characters have been lost through change in the information content of their genomes. Two dramatic changes that epitomize such evolutionary transformations are the gain of novel antifreeze proteins, which are obligatory for survival in icy seawater, by most notothenioids and the paradoxical loss of respiratory haemoproteins and red blood cells, normally deemed indispensable for vertebrate life, by the species of a highly derived notothenioid family, the icefishes. Here, we review recent advances in our understanding of these traits and their evolution and suggest future avenues of investigation. The formerly coherent paradigm of notothenioid freeze avoidance, developed from three decades of study of antifreeze glycoprotein (AFGP) based cold adaptation, now faces challenges stemming from the recent discovery of antifreeze-deficient, yet freeze-resistant, early notothenioid life stages and from definitive evidence that the liver is not the physiological source of AFGPs in notothenioid blood. The resolution of these intriguing observations is likely to reveal new physiological traits that are unique to the notothenioids. Similarly, the model of AFGP gene evolution from a notothenioid pancreatic trypsinogen-like gene precursor is being expanded and refined based on genome-level analyses of the linked AFGP loci and their ancestral precursors. Finally, the application of comparative genomics to study evolutionary change in the AFGP genotypes of cool-temperate notothenioids from sub-Antarctic habitats, where these genes are not necessary, will contribute to the mechanistic understanding of the dynamics of AFGP gene gain and loss. In humans and most vertebrates, mutations in the alpha- or beta-globin genes or defects in globin chain synthesis are causes of severe genetic disease. Thus, the 16 species of haemoglobinless, erythrocyte-null icefishes are surprising anomalies -- in fact, they could only have evolved and thrived due to relaxed selection pressure for oxygen-binding proteins in the cold, oxygen-rich waters of the Southern Ocean. Fifteen of the sixteen icefish species have lost most of the adult alphabeta-globin locus and retain only a small 3' fragment of the alpha-globin gene. The only exception to this pattern occurs in Neopagetopsis ionah, which possesses a disrupted alphabeta-globin gene complex that probably represents a non-functional intermediate on the evolutionary pathway to near total globin gene extinction. By contrast, six of the icefish species fail to express myoglobin. The absence of myoglobin expression has occurred by several independent mutations and distinct mechanisms. Haemoprotein loss is correlated with dramatic increases in cellular mitochondrial density, heart size, blood volume and capillary bed volume. Evolution of these compensatory traits was probably facilitated by the homeostatic activity of nitric oxide, a key modulator of angiogenesis and mitochondrial biogenesis. These natural knockouts of the red blood cell lineage are an excellent genomic resource for erythroid gene discovery by comparative genomics, as illustrated for the newly described gene, bloodthirsty.

State-dependent life history plasticity in Sacramento River winter-run chinook salmon (Oncorhynchus tshawytscha): interactions among photoperiod and growth modulate smolting and early male maturation

An experiment was performed to determine the relative effects of photoperiod at emergence and growth rate on smolting pattern and early male maturation rate in Sacramento River (California, USA) winter-run chinook salmon (Oncorhynchus tshawytscha) (listed as endangered under the US Endangered Species Act). Fry were ponded on the same day but at three different points in the seasonal photoperiod cycle (using artificial lighting) spanning the natural range of emergence timing in this population. Significant increases in gill Na+,K+-ATPase activity and seawater survival were found during March and April in all treatments, similar to yearling smolting patterns found in many salmonids. Fish that emerged early and grew at a relatively high rate also demonstrated signs of smolting in August–November. Male maturation was growth dependent, with HiFeed groups maturing at a rate double that found in LoFeed groups. Male maturation was also photoperiod dependent with a linear relation found between emergence date and rate of male maturation. These results demonstrate that individual life history pattern was variable and dependent on emergence timing and growth rate.

β‐Oxidation capacity in liver increases during parr‐smolt transformation of Atlantic salmon fed vegetable oil and fish oil

Atlantic salmon Salmo salar were fed diets containing 100% fish oil (FO; capelin oil) or 100% vegetable oil (VO) from start of feeding until the fish reached the size of 2·5 kg. Samples were taken during the period of the parr‐smolt transformation (October 2002 to February 2003). The VO diet consisted of a blend of 55% rapeseed oil, 30% palm oil and 15% linseed oil to maintain the sum of saturated, monounsaturated and polyunsaturated fatty acids between the two diets, although with differences in the individual chain length of fatty acids. Na+/K+‐ATPase activity in the gills, total β‐oxidation capacity in muscles and liver and total lipid, glycogen and dry matter content in the muscles were measured during the parr‐smolt transformation and after seawater transfer. Na+/K+‐ATPase activity in gills increased prior to seawater transfer, showing an adaptation for seawater survival. Major changes in the lipid and glycogen content in the fillet and in β‐oxidation capacity were found in the tissues measured. β‐oxidation capacity increased significantly in liver and decreased in red muscle, prior to seawater transfer, giving liver an important role in energy production during this period. Results also indicated that feeding Atlantic salmon a diet where 100% of FO was replaced with VO did not have any negative effects on lipid metabolism during parr‐smolt transformation.

NOVEL IN VITRO METHOD TO STUDY FISH INTESTINE

Early in life, salmonid fishes move from a freshwater existence to a life in seawater, requiring a complete overhaul of their osmoregulatory systems. The vertebrate intestine is a major osmoregulatory organ and in fish,intestinal salt and water uptake is essential for maintaining water balance. Solute and water movement is mainly driven across the intestinal epithelium by the Na+, K+-ATPase, an ATP-requiring enzyme located on the basolateral membrane or blood side of the intestinal cell. Cortisol, a stress hormone, is thought to mediate the necessary osmoregulatory adaptations required for a salmonid's transformation between environments. It has been suggested that intestinal Na+, K+-ATPase activity, which becomes elevated in preparation for seawater survival, is stimulated by cortisol in many salmonid fishes. However, the influence of cortisol on fish intestine has never been measured directly. To determine the direct effects of cortisol on the intestine during salinity transfer, an in vitrointestinal tissue culture system is needed.Thus, Philip Veillette and Graham Young set out to develop an intestinal tissue culture system from freshwater-adapted sockeye salmon Oncorhynchus nerka by adapting methods used for culturing salmon gill filaments. They decided to culture the pyloric ceca (appendages attached to the salmon's intestines) and the posterior intestine based on their significant roles in absorption and osmoregulation. They cut each intestinal region into pieces,incubated the intestinal preparations at 14°C and gassed them daily with a 95% O2, 5% CO2 mixture to keep the cells alive. To see if their tissue culture was still viable after 3 or 6 days in culture,Veillette and Young examined the preparations using light and transmission electron microscopy. Sure enough, they noticed intact nuclei and organelles,which meant that the intestinal cells were still functional; they had an in vitro intestinal tissue culture.Veillette and Young could now test whether salmon intestinal Na+, K+-ATPase activity is stimulated by cortisol. In the absence of cortisol, the activity of Na+, K+-ATPase in the intestine preparation declined after several days in culture. However,when Veillette and Young treated the preparations with cortisol, they noticed significantly maintained Na+, K+-ATPase activity in both segments of the intestine, demonstrating for the first time that cortisol acts directly on the teleost intestine. The response to cortisol was dose-dependent and specific for cortisol over other corticosteroids within a physiological range. To see if they could replicate these results in vivo, they implanted salmon with slow-release cortisol, elevating plasma cortisol concentrations in these fish. Just as they had found in vitro,cortisol increased Na+, K+ ATPase activity in both intestinal segments in live fish.Using a novel approach, Veillette and Young have shown that the salmon pyloric ceca and the posterior segment of the intestine are direct targets for the osmoregulatory actions of cortisol in salmonids. Their novel culture system could potentially be used to examine the effects of a variety of neuroendocrine factors on the intestine under many different physiological conditions.