Vulnerability of late larval and early juvenile Atlantic herring, Clupea harengus, to predation by whiting,Merlangius merlangus

Laboratory experiments investigated changes in the vulnerability of herring to predation by whiting during growth from <34 to >80mm in length, Premetamorphic herring (<50mm) failed to react to c . 50% of attacks by the predator, but this was reduced to c . 20% in postmetamorphic fish. Premetamorphic herring failing to react had c. 30% probability of survival due to unforced errors by the predator (unsuccessful attacks that did not elicit a reaction by the prey), but these errors did not occur after herring metamorphosis. The loss of the advantage of lower conspicuousness following metamorphosis was counterbalanced by increased reactivity. Antipredator benefits should increase with schooling behaviour (first evident in experiments at c . 50 mm), so predation mortality should decrease in postmetamorphic herring in the sea. Metamorphosis itself would be associated with high predation risk since conspicuousness is enhanced but reactivity and schooling behaviour are still not fully developed.     

Influence of temperature on evasive responses of Atlantic herring larvae attacked by yearling herring, Clupea harengus L.

Predation encounters were staged in the laboratory between yearling herring, Clupea harengus L., 66 to 104 mm t.l. , and herring larvae, 8 to 30 mm t.l. ., at 8,11 and 14 o C. Video records were used to quantify prey behaviour. Prey responsiveness, reactive distance, response latency, and apparent looming threshold were not affected by temperature. Response speeds increased with temperature. Predator error rate and capture success showed no consistent thermal effects. Although the experiments could not fully evaluate the influence of temperature on the predators, results suggest that the predator's performance largely governs the outcome of an attack on a larva and that higher temperatures favour the predator by increasing the frequency of its encounter with prey.     

Drinking and water absorption by the larvae of herring (Clupea harengus) and turbot (Scophthalmus maximus)

The efficiencies of water absorption from the guts of the larvae of herring ( Clupea harengus L.) and turbot ( Scophthalmus maximus L.) were estimated by two methods, The first method was based on the differences in the rates of accumulation, by drinking, and clearance from the gut of radiolabelled inert markers. The second method used the equilibrium level of radioactivity in the larvae to measure the concentration of the markers in the gut above background as water is absorbed from the gut. Water absorption efficiencies for herring larvae drinking sea water were estimated to be 77% using both methods. When external salinity was reduced to 50% sea water, drinking rates and water absorption efficiency in herring larvae fell substantially.
Estimates of water absorption efficiency of seawater-adapted turbot larvae were similar (71–84%) to that of herring using both methods. Although temperature had a marked effect on both the rate of drinking and water absorption, there was no significant thermal effect on the efficiency of absorption from the guts of turbot larvae. The limitations of the techniques and the implications of the estimates in terms of water balance in fish larvae are discussed.     

Differential utilization of storage lipids and storage proteins by Northwest Atlantic herring (Clupea harengus harengus)

Utilization of storage lipids and storage proteins by non-feeding north-west Atlantic herring was assessed under conditions of: (1) concurrent gonad maturation and overwintering periods with differing rates of gonad development for males and females (spring-spawncrs); (2) overwintering, reproductively dormant and spent males and females (autumn-spawners); and (3) approximately equivalent rates of gonad development during late summer for males and females (autumn-spawners). Storage lipids were depleted by all non-feeding fish but storage proteins were depleted only by herring with measurable gonad development during the observation period independently of season (female spring-spawners, maturing male and female autumn-spawners). The analyses indicate that storage lipids sustain routine and active metabolism while storage proteins are utilized to develop gonad. Therefore, the relative investment into reproduction versus routine and active metabolism can be evaluated separately for non-feeding herring using readily obtainable tissue proximate composition data.     

Comparative study of early-life survival variability of herring Clupea harengus, in the north-eastern Atlantic

Variation in the survival of herring between the egg stage and the age of recruitment to the spawning population has been examined for seven Atlantic herring populations in northern European waters. The sources of the variation have been partitioned between density-dependent and density-independent factors. The magnitude of the density-independent component was found to be related to the scale of the processes controlling the dispersion and distribution of larvae from the various populations. We conclude that the spawning strategies of some populations are adapted to oceanographic conditions to maximize the probability of a particular larval transport pattern, although no single model could account for all spawning strategies.     

Effect of different holding regimens on the intestinal microflora of herring (Clupea harengus) larvae.

The aerobic intestinal microflora of 2-week-old herring (Clupea harengus) larvae was characterized by using conventional microbiological methods and electron microscopy. Larvae were hatched and kept in filtered seawater or in seawater with penicillin and streptomycin. The gastrointestinal tract of herring larvae is essentially a straight tube divided into two compartments. Light microscopy revealed bacteria present in a progressively increasing amount throughout the length of the gastrointestinal tract from esophagus to anus. The posterior region of the intestinal lumen appeared completely occluded with bacteria. The intestinal microflora consisted mainly of members of the genera Pseudomonas and Alteromonas in the larvae incubated in filtered seawater, whereas Flavobacterium spp. dominated in larvae exposed to antibiotics. The intestinal microflora of untreated fish larvae was sensitive to all tested antibiotics, whereas multiple resistance was found in the intestinal microflora of the group given antibiotics. Thus, a dramatic change in the microflora resulted from incubation with antibiotics. Nonpigmented yeasts were detected in both larval groups. Ciliated epithelial cells were observed in the midgut, probably propeling bacteria towards the hindgut, where endocytosis of bacteria has been demonstrated. These findings suggest that transport and sequestering mechanisms resembling those of invertebrates may be found in the gut of fish larvae. The possible significance for larval health and nutrition is discussed.     

Experimental studies on the migration of Anisakis sp. larvae (Nematoda: ascaridida) into the flesh of herring, Clupea harengus L.

In two experiments, a batch of 38 herring from Shetland was gutted immediately on capture (0 h) and further batches were gutted 14 and 37 h after capture and storage on ice. The numbers of Anisakis larvae in the body-cavity and in the flesh (detected by pepsin-HCl digest) were then counted. The proportion of fish with worms in the flesh was higher at 14 and 37 h than at 0 h. The percentage of the total worm burden in the flesh increased between cash each time interval, which suggests that a large-scale migration of larvae into the flesh occurs in ungutted fish. There was a positive association between the numbers of larvae in the viscera and the numbers in the flesh. Most larvae occurred in the hypaxial muscles. The results are discussed in relation to the observations of earlier workers.     

Effect of different holding regimens on the intestinal microflora of herring (Clupea harengus) larvae.

The aerobic intestinal microflora of 2-week-old herring (Clupea harengus) larvae was characterized by using conventional microbiological methods and electron microscopy. Larvae were hatched and kept in filtered seawater or in seawater with penicillin and streptomycin. The gastrointestinal tract of herring larvae is essentially a straight tube divided into two compartments. Light microscopy revealed bacteria present in a progressively increasing amount throughout the length of the gastrointestinal tract from esophagus to anus. The posterior region of the intestinal lumen appeared completely occluded with bacteria. The intestinal microflora consisted mainly of members of the genera Pseudomonas and Alteromonas in the larvae incubated in filtered seawater, whereas Flavobacterium spp. dominated in larvae exposed to antibiotics. The intestinal microflora of untreated fish larvae was sensitive to all tested antibiotics, whereas multiple resistance was found in the intestinal microflora of the group given antibiotics. Thus, a dramatic change in the microflora resulted from incubation with antibiotics. Nonpigmented yeasts were detected in both larval groups. Ciliated epithelial cells were observed in the midgut, probably propeling bacteria towards the hindgut, where endocytosis of bacteria has been demonstrated. These findings suggest that transport and sequestering mechanisms resembling those of invertebrates may be found in the gut of fish larvae. The possible significance for larval health and nutrition is discussed.     

Cholecystokinin (CCK) in Atlantic herring (Clupea harengus L.) - ontogeny and effects of feeding and diurnal rhythms

Neural and alimentary cholecystokinin (CCK) levels in Atlantic herring, Clupea harengus, were analyzed from hatching to 40days after hatching (DAH). The head compartment representing the neural pool was quantitatively dominant (>80% of the total CCK content) while the digestive tract pool represented 6-10%. During ontogeny the CCK level in whole larvae increased almost 15-fold from 0 to 40 DAH, being particularly marked from 14 to 20 DAH. Larvae of 24 to 26 DAH were examined for potential occurrence of a circadian rhythm and to analyze the effects of feeding. Fed and fasted larvae were significantly different, where fed larvae showed higher CCK levels. There were large fluctuations in CCK levels analyzed at 3h intervals without an apparent diurnal pattern. Shorter sampling intervals of 1h in the morning when lights were switched gradually on and food was offered to the larvae demonstrated a marked drop in the relative gut CCK levels and a concurrent increase in the CCK carcass to gut ratio, 1h after introduction of food followed by a return to prefeeding levels after 2h. This response probably results from a release and re-synthesis of CCK in the gut after initiation of feeding. Taken together, these results support earlier reports that CCK participates in the regulation of digestive processes in herring larvae, but CCK does not seem to have a circadian rhythm independent of feeding.     

Lipid classes and fatty acid composition of rotifers (Brachionus plicatilis) fed two algal diets

Rotifers (Brachionus plicatilis), maintained on baker's yeast, were fed for 24h upon two algal diets, Isochrysis galbana (diet A) and Isochrysis galbana + Nannochloropsis gaditana (diet B). (These algal diets were selected for their potential use as essential fatty acid (EFA) boosters, taking into account the requirements of fish larvae). The effect of these algal diets on total lipid content, lipid classes and fatty acid composition was studied. The total lipid content increased after feeding upon both diets but no significant differences were found between the two types. Neutral lipid and polar lipid contents increased and a positive correlation was observed between the neutral lipids content of rotifers and that of the food supplied. However, the content of polar lipids in rotifers did not depend upon that of the diet. The increase in neutral lipid content was found to be higher in rotifers fed upon diet B, compared to diet A which increased the phospholipid content. Non-enriched rotifers contained only small amounts of polyenoic fatty acids, i.e. 18:3n-6, 18:3n-3, 20:4n-6, 20:5n-3 and 22:6n-3, the contents of which increased significantly by feeding both diets. The EFA composition (20:4n-6, 20:5n-3 and 22:6n-3) of neutral lipids and phopholipids in rotifers reflected the EFA composition of each diet. Diet B-fed rotifers had the highest content in 20:4n-6 and 20:5n-3, whereas rotifers fed diet A and the highest 22:6n-3 content. The mixed diet I. galbana + N. gaditana enhanced substantially the composition of lipid classes i.e. neutral lipids and of n-3 PUFA of rotifers in comparison with Isochrysis or yeast diets.     

Effect of selenium supplementation on polyunsaturated fatty acids in rats

The purpose of this work was to study plasma, adipose tissue, and liver fatty acids percentages of Wistar rats that drank water supplemented with several levels of sodium selenite for 1, 3, and 6 mo. In a general way, percentages of saturated, monounsaturated, and polyunsaturated fatty acids of supplemented groups were not different from those obtained with nontreated animals in the analyzed tissues. However, in rats supplemented with 0.5 ppm Se, mainly in adipose tissue, a polyunsaturated fatty acids increase (p<0.005) was observed for all times of treatment. This could suggest that 0.5 ppm Se supplement probably exercises a protective role on polyunsaturated fatty acids in that tissue. Supplements of 6.0, 15.0, and 54.0 ppm Se did not change unsaturation levels of fatty acids in the analyzed tissues.     

Alteration of the acyl chain composition of free fatty acids,acyl coenzyme A and other liPids by dietary polyunsaturated fats

Dietary alterations were used to demonstrate selective handling of fatty acids during their redistributionin vivo. Differences in the mol Per cent of individual acyl chains in the non-esterified fatty acid, acyl-coenzyme A and PhosPholiPid fractions reflected a result of relative Precursor abundance combined with enzymic selectivities. Selective distributions were observed in the utilization of individual acyl chains between 16:0 and 18:0, 18:1 and 18:2, and among 20:3, 20:4 and 20:5, 22:6 by ligase(s), hydrolase(s) and acyl-transferases. The variations in the mol Per cent of linoleate Present in the acyl-coenzyme A fraction of liver relative to that in the non-esterified fatty acids suggested anin vivo regulation of the level of linoleoyl-coenzyme A that influenced the synthesis of both arachidonoyl-coenzyme A and lipids. The greater abundance of eicosaPentaenoic acid in the free fatty acid fraction relative to that in the acyl-coenzyme A fraction may increase the ability of dietary 20: 5n-3 to be an effective inhibitor of the synthesis of Prostaglandins derived from 20:4n-6.     

The fatty acid and sterol composition of two marine dinoflagellates

The fatty acid, sterol and chlorophyll pigment compositions of the marine dinoflagellates Gymnodinium wilczeki and Prorocentrum cordatum are reported. The fatty acids of both algae show a typical dinoflagellate distribution pattern with a predominance of C₁₈, C₂₀ and C₂₂ unsaturated components. The acid 18:5ω3 is present at high concentration in these two dinoflagellates. G. wilczeki contains a high proportion (93.4%) of 4-methyl-5α-stanols including 4,23,24-trimethyl-5α-cholest-22E-en-3β-ol (dinosterol), dinostanol and 4,23,24-trimethyl-5α-cholest-7-en-3β-ol reported for the first time in dinoflagellates. The role of this sterol in the biosynthesis of 5α-stanols in dinoflagellates is discussed. P. cordatum contains high concentrations of a number of δ ²⁴⁽²⁸⁾-sterols with dinosterol, 24-methylcholesta-5,24(28)-dien-3β-ol, 23,24-dimethylcholesta-5,22E-dien-3β-ol, 4,24-dimethyl-5α-cholest-24(28)-en-3β-ol and a sterol identified as either 4,23,24-trimethyl- or 4-methyl-24-ethyl-5α-cholest-24(28)-en-3β-ol present as the five major components. The role of marine dinoflagellates in the input of both 4-methyl- and 4-desmethyl-5α-stanols to marine sediments is discussed.     

Effect of exogenous sterols on the growth and fatty acid composition of the oomycetePythium debaryanum

Exogenous ergosterol and cholesterol were found to affect the growth and lipogenesis of the oomycete fungusPythium debaryanum, which is unable to synthesize de novo steroid compounds. These sterols stimulated the growth of the fungus during its submerged cultivation in glucose-peptone medium. This was accompanied by the shortening of the lag phase, the lengthening of the period of active growth, and by a 3.7-or 4.3-fold increase in the maximum biomass in response to the addition of ergosterol or cholesterol, respectively. In the presence of ergosterol, the cellular content of polyenoic fatty acids increased, and the relative content of eicosapolyenoic fatty acids reached 31.4% of the total amount of fatty acids in cells. Conversely, cholesterol decreased the cellular content of polyenoic acids, and the relative content of eicosapolyenoic acids fell to 19.6% of the total amount of fatty acids. It may be inferred that exogenous sterols enhance the yield of pharmacologically active polyenoic acids because of the growth stimulation.     

Effects of larvae ontogeny, turbidity, and turbulence on prey attack rate and swimming activity of Atlantic herring larvae

The effect of turbulence, light level, and ontogeny on herring larva's attack rate and swimming activity was tested in a previous study. However, during larval seasons (spring and autumn), water clarity is frequently impaired by alga blooms, which also most probably will affect larva feeding rate. Therefore, this study was to investigate the effects of turbidity, turbulence, and ontogeny on the attack rate and swimming activity of herring larvae. By adding diatomaceous earth (DE) to the water, three turbidity levels were established: 0, 35, and 80 Jackson Turbidity Unit [JTU; which coincide with a beam attenuation (c) of 0.1, 2.5, and 4.8 m⁻¹, respectively]. An unfavourable (8×10⁻⁶ W/kg) and a favourable turbulence level (1×10⁻⁶ W/kg) were chosen based on results from the earlier study. The results show that intermediate turbidity (35 JTU) has a positive effect on the attack rate of smaller larvae (20 mm), while high turbidity (80 JTU) has a negative effect on attack rate of all tested larvae size groups. In general, attack rate was lower at the highest turbulence compared to the low level, independent of turbidity level. However, there was one exception, when turbidity was at the highest, the largest larvae (29 mm) seemed to gain from feeding in the highest turbulence level. The overall activity level was higher in the presented study than in the earlier study without turbidity. The favourable turbidity level (35 JTU) coincides with turbidity levels normally found at the equivalent depth during spring and autumn blooms in the area of where the experimental larvae originate. In addition, turbidity's effect on light absorbtion and how it influences the maximum feeding depth of the larva are discussed.     

Assessment of lipid and essential fatty acids requirements of black seabream (Spondyliosoma cantharus) by comparison of lipid composition in muscle and liver of wild and captive adult fish

The primary aim of the present study was to compare the contents of total lipid, lipid classes and their associated fatty acids in muscle and liver of wild and one-year captive black seabream (Spondyliosoma cantharus) adults, in order to elucidate the lipid and fatty acids requirements of this fish species of potential interest for aquaculture. The total lipid contents (TL) of muscle and liver of the captive fish were 2.5-fold greater than those of the wild fish. In consequence, contents of triacylglycerols were much higher in tissues of the captive fish. Distribution of fatty acids in total lipids and lipid classes of muscle and liver was also different between both groups of fish. For instance, percentages of 20:4n−6, 20:5n−6 and 22:6n−3 were considerably higher in the wild fish, whereas 18:1, 20:1, and 22:1n−9 as well as 18:2n−6 and 20:5n−3 were more abundant in the captive fish. These results suggest that the lipid composition of the commercial diet supplied to the captive black seabream differed greatly from that of the diet consumed by the fish in the wild, which hypothetically contains the desirable composition for the lipid nutrition of this fish species. Despite the good growth and survival achieved by the black seabream after one year in captivity, the significant accumulation of lipids and the imbalance of essential fatty acids in their muscle and livers, together with the absence of spawning, suggest that future research on the lipid requirements of this omnivorous species is necessary in order to establish whether the administration of currently available aquaculture formulated feeds is adequate for good black seabream performance and reproduction.     

Particulate fatty acids in two small Siberian reservoirs dominated by different groups of phytoplankton

SUMMARY 1. We studied the composition of fatty acids (FAs) in the seston from two small freshwater reservoirs (Bugach and Lesnoi) with distinct periodicity of domination by cyanobacteria and eukaryotic algae during the growth season.
2. The diatoms in the both reservoirs were characterised by a high content of 14:0 and C16 unsaturated acids, whereas that of the essential FA 20:5ω3 [eicosapentanoic acid (EPA)] was low. The correlation between this polyunsaturated FA (PUFA) and diatom biomass was not significant in either reservoir. The percentage of 20:5ω3 in seston significantly correlated with the biomass of euglenophyta in Bugach and dinophyta in Lesnoi. Hence the diatoms, usually referred as a valuable food for zooplankton, were not an important source of the essential PUFA in these systems.
3. The dominant cyanobacteria in Bugach, and the green algae in Lesnoi, both contained the same marker acids: 18:3ω3 and 18:2ω6. Hence, a discrimination between these two phytoplanktonic groups on the basis of FA biomarkers may be difficult in some cases.
4. We found no significant correlation between the content of 20:5ω3 in seston and the biomass of the dominant daphniids in either reservoir. This is contrary to expectations, based on the literature, that EPA is generally important. Rather, the biomass of the two dominant Daphnia species in Bugach correlated strongly with the content of 18:3ω3 in the seston. The cyanobacteria were a probable source of this ω3 FA for Daphnia . We conclude that EPA is not always important for Daphnia populations although, in such cases, some other PUFA (e.g. 18:3ω3) might be related to their growth.     

Trans fatty acids in hydrogenated fat inhibited the synthesis of the polyunsaturated fatty acids in the phospholipid of arterial cells

Our hypothesis that the trans fatty acids in hydrogenated fat inhibited the synthesis of polyunsaturated fatty acids in the phospholipid of arterial cells was tested with five groups each with six pregnant porcine fed from d 35 of gestation and during lactation. The basal diet contained 2% corn oil (control). The other four diets included the control + 10% butter or 10% hydrogenated fat plus two levels of Mg. Plasma, milk and aortic phospholipid fatty acids, phospholipid composition and calcium content of the aorta from the piglets were determined. At 48 +/- 2 d of age, the aorta phospholipid of piglets from porcine fed hydrogenated fat contained a significantly higher concentration of linoleic acid, less arachidonic acid, and less long chain polyunsaturated fatty acid (PUFA) than did piglets from porcine fed either butterfat or the control diet. Mg had no effect. These changes in composition in piglets from porcine fed hydrogenated fat indicate that trans fat inhibits the metabolic conversion of linoleic acid to arachidonic acid and to other n-6 PUFA. The aortic calcium content data showed a significant interaction of calcium concentration with age. We concluded: 1) that dietary trans fat perturbed essential fatty acid (EFA) metabolism which led to changes in the phospholipid fatty acid composition in the aorta, the target tissue of atherogenesis, 2) this inhibition of EFA to PUFA by the isomeric fatty acids in hydrogenated fat is a risk factor in the development of coronary heart disease.     

Inhibitory action of polyunsaturated fatty acids on IMP dehydrogenase

We screened the inhibitor of mouse inosine 5'-monophosphate dehydrogenase (IMPDH) type II from natural compounds, and found that a fatty acid, linoleic acid (C18:2), inhibited IMPDH activity. In the C18:2 fatty acid derivatives, all trans-configuration (i.e., linoelaidic acid), ester form, alcohol form, and addition of the hydroxyl group of linoleic acid had no effect on inhibitory activity. Therefore, both parts of a carboxylic acid and an alkyl chain containing cis-type double bonds of fatty acid might be essential for inhibition. Among the various carbon atom lengths and double bonds of fatty acids examined, the strongest inhibitor was C20:2-fatty acid, eicosadienoic acid, and 50% inhibition was observed at a concentration of 16.1 microM. Eicosadienoic acid induced the inhibition of IMPDH activity and was competitive with respect to IMP (K(i)=3.1 microM). For inhibitory effect, the C20-fatty acids ranked as follows: C20:2>C20:3>C20:1> C20:4>C20:5, and C20:0 showed no inhibition. The energy-minimized three-dimensional structures of linear-chain C20-fatty acids were calculated, and it was found that a length of 20.7-22.5A and width of 4.7-7.2A in the fatty acid molecular structure was suggested to be important for IMPDH inhibition. Docking simulation of C20-fatty acids and mouse IMPDH type II, which was homology modeled from human IMPDH type II (PDB code: 1NF7), was performed, and the fatty acid could bind to Cys331, which is a amino acid residue of the active site, competitively with IMP. Based on these results, the IMPDH-inhibitory mechanism of fatty acids is discussed.