n‐3 and n‐6 fatty acid bioconversion abilities in Eurasian perch (Perca fluviatilis) at two developmental stages

The aim of this work was to study the fatty acid (FA) bioconversion ability in Eurasian perch fed with diets differing in their polyunsaturated fatty acids (PUFA) from n‐3 and n‐6 series content at two development stages: adults in exogenous vitellogenesis, and juveniles during the on‐growing phase. Duplicate groups of adults and juveniles were fed for 12 weeks with four diets: D1 and D2, two diets prepared with fish oil partially or totally as the lipid source, and so containing long‐chain PUFA (LC‐PUFA). Those two diets differed by their n‐3/n‐6 FA dietary ratio (0.2 and 7.0, respectively), D1 being characterized by a high n‐6 LC‐PUFA level, while D2 had a high level of n‐3 LC‐PUFA. D3 and D4 were constituted only with vegetable oils, and were therefore devoid of LC‐PUFA. D3 was characterized by a high level of 18:2 n‐6 (n‐6/n‐3 ratio of 0.3), while D4 was characterized by a high level of 18:3 n‐3 (n‐3/n‐6 ratio of 1.9). Both groups of fish were able to elongate and desaturate the 18:3 n‐3 precursor into eicosapentaenoic acid and docosahexaenoic acid, regarding the FA profile of livers. Furthermore, total elongation/desaturation from [1‐¹⁴C]18:3 n‐3 of LC‐PUFA was higher in fish fed with the high dietary 18:3 n‐3 level compared to the diet rich in n‐3 LC‐PUFA. By opposition, the bioconversion of 18:2 n‐6 into LC‐PUFA was limited, regarding the elongation/desaturation activity of LC‐PUFA from [1‐¹⁴C]18:2 n‐6. In view of the great ability for bioconversion of n‐3 FA, linseed oil is a promising alternative to fish oil in formulating feed for juveniles perch as there were no differences in terms of specific growth rate between the treatments, but adults undergoing maturation should have at least partially LC‐PUFA in their diet, particularly arachidonic acid (ARA) which is important during maturation, as breeders are not able to bioconvert 18:2 n‐6 into ARA.     

Egg and larval quality,and egg fatty acid composition of Eurasian perch breeders (Perca fluviatilis) fed different dietary DHA/EPA/AA ratios

In Eurasian perch (Perca fluviatilis), the variability in spawning quality is a major limiting factor for successful production, especially when breeders are fed with an artificial diet. The influence of the dietary DHA/EPA/AA ratio on the egg and larval quality and on the fatty acid and lipid class composition of eggs has been investigated in perch broodstock. Two experimental diets (16% lipids) with two different DHA/EPA/AA ratios, D1 (3/2/2) and D2 (23/9/1), were compared with a natural diet consisting of cultured carp juveniles, CC (10/10/1) and with a commercial diet for salmonids, CDS (14/16/1). Percentages of fertilization and hatching were comparable between fish fed D1, D2 and CC, with the highest hatching rate observed for D1 (63.5 ± 3.8%). These diets supported better values than the CDS. Larval survival and TL50 observed after osmotic stress were higher for the D1 group, followed by larvae produced by fish fed D2 and CC. Larvae from fish fed D1, D2 and CC were significantly more robust than larvae from the CDS group. Differences were observed regarding the fatty acid (FA) profile in the eggs, which was related to the dietary FA composition. The results indicate that a ratio of 3/2/2 seemed to be effective for obtaining eggs and larvae of good quality.     

Digestibility of microbial and mussel meal for Arctic charr (Salvelinus alpinus) and Eurasian perch (Perca fluviatilis)

Apparent digestibility coefficients (ADCs) for four protein‐rich alternative feed ingredients, intact baker's yeast (Saccharomyces cerevisiae), extracted baker's yeast (S. cerevisiae), zygomycetes (Rhizopus oryzae) and blue mussel (Mytilus edulis), were determined for Arctic charr (Salvelinus alpinus) and Eurasian perch (Perca fluviatilis). Diets contained 30% of test ingredients, and ADCs were compared to a reference diet containing fish meal. For Arctic charr, ADCs for dry matter (DM, 71–99%), sum of amino acids (SAA, 84–99%) and gross energy (70–99%) were significantly lower for intact S. cerevisiae than for extracted S. cerevisiae, R. oryzae and M. edulis. The ADCs for the indispensable amino acids (IAA) in Arctic charr varied between 84% and 99%. Significant differences were found in ADCs for IAA between the test ingredients for Arctic charr, with higher values for extracted S. cerevisiae and M. edulis. The ADCs in Eurasian perch varied between 83% and 95% for DM, 89% and 98% for CP, 92% and 100% for SAA, 81% and 96% for gross energy. No significant differences were found for ADCs between the test ingredients in Eurasian perch, indicating a species effect on digestibility. Furthermore, the absence of intact cell walls had a positive effect on digestibility of S. cerevisiae for Arctic charr.     

Size‐related oxygen consumption and ammonia excretion of Eurasian perch (Perca fluviatilis L.) reared in a recirculating system

Oxygen consumption (OC) and ammonia excretion rates (AE) of perch were measured under commercial‐like conditions (temperature 23.3 °C) in both fed (F) and feed‐deprived groups (D). Measurements were taken in triplicate in six sized batches of perch ranging from 44.8 to 336.2 g. The mean daily OC was 288.3–180.6 mg O₂ kg^?1 h^?1 for group F fish ranging in size from 44.8 to 279.4 g body weight. The mean daily AE expressed as total ammonia nitrogen (TAN) was 13.8–5.2 mg TAN kg^?1 h^?1 in the same groups. Daily peaks of OC in group F perch were observed 6 h after the onset of feeding for each size group with relatively stable values up to the end of feeding. Peaks of daily AE in group F perch were observed 10 h after the onset of feeding in each size group, with a rapid decrease up to 16 h after onset. In group D, OC was 181.1–110.5 mg O₂ kg^?1 h^?1 in the weight range 57.9–336.2 g. The daily mean AE was 1.7–0.5 TAN kg^?1 h^?1 in this group. No dramatic peaks of OC and AE were observed in group D perch.     

Effects of dietary lipid level and n‐3/n‐6 fatty acid ratio on growth,fatty acid composition and lipid peroxidation in Russian sturgeon Acipenser gueldenstaedtii

The growth performance, fatty acid composition, hepatic lipid content, hepatic somatic index and lipid peroxidation in Russian sturgeon were investigated using diets containing three lipid levels 50 g kg^?1 (L5), 150 g kg^?1 (L15) and 250 g kg^?1 (L25) and three n‐3/n‐6 fatty acid ratios (1 : 3, 1 : 1 and 3 : 1) for 8 weeks. Weight gain significantly increased with the increase in dietary lipid levels at n‐3/n‐6 fatty acid ratios of 1 : 3 and 1 : 1, but not at the 3 : 1 ratio. Correspondingly, fish survival gradually decreased with the increase in dietary lipid at the 3 : 1 n‐3/n‐6 fatty acid ratio. The dietary lipid level significantly affected the composition of whole‐body fatty acid. The retention of highly unsaturated fatty acid dramatically decreased at the level of 250 g kg^?1 dietary lipid. The liver malondialdehyde increased with the increase in dietary lipid levels and the n‐3/n‐6 fatty acid ratios. The contents of lipid and triglyceride in the liver and the hepatic somatic index also increased with the increase in dietary lipid. The diet combination of L25 + 3 : 1 showed the highest aspartate transaminase and alanine transaminase, indicatives of hepatic injury. This study indicates that the L25 + 1 : 3 diet can improve fish growth performance, whereas the L25 + 3 : 1 diet may lead to poor growth performance due to high lipid peroxidation.     

Abundance, depth distribution, diet composition and growth of perch (Perca fluviatilis) and burbot (Lota lota) larvae and juveniles in the pelagic zone of Lake Constance

Abstract— Surveys of larval and juvenile fish in the pelagic zone were made in Lake Constance between April and July 1994 with a plankton net. Perch ( Perca fluviatilis ) and burbot ( Lota lota ) were caught persistently, while other species were found only occasionally. Perch and burbot coexisted in the pelagic zone; both species were found first in mid-May, reached peak density in June, and disappeared from the pelagic zone in late July. However, the abundance of perch was much higher than that of burbot. Perch were distributed mainly near the surface, whereas burbot were more abundant at the deeper strata of 5 and 10 m, exhibiting habitat segregation. Perch fed mainly on copepods and positively selected them during their first month of life, and afterwards, they consumed principally on Daphnia , while burbot fed mainly on copepods and positively selected them throughout the study period. Perch grew significantly faster than burbot, and the mean lengths of perch were about 3 times greater than that of burbot in July. The results demonstrate that perch and burbot were the main species of pelagic larvae in Lake Constance between May and July, and that the two species differed somewhat in depth distribution, diet composition and growth.     

Influence of dietary linoleic acid (18:2n‐6) and α‐linolenic acid (18:3n‐3) ratio on fatty acid composition of different tissues in freshwater fish Songpu mirror carp,Cyprinus Carpio

Six isonitrogenous and isoenergetic purified diets were formulated to feed Songpu mirror carp for 60 days. The control diet (CD) was only supplemented with soybean oil. The other five experimental diets contained soybean oil, linseed oil and lard oil blended at various inclusion levels to attain different linoleic acid (LA)/α‐linolenic acid (LNA) ratios (0.53, 1.04, 2.09, 3.95, 6.82) with a constant total C₁₈ polyunsaturated fatty acids (PUFA; LA+LNA, 2% dry weight) content. The fatty acid (FA) profiles of hepatopancreas, dorsal muscle, intestine, intraperitoneal fat (IPF), spleen and kidney reflected those of the diets, but with some differences. The spleen showed the lowest correlation with diet compared with other tissues, followed by the hepatopancreas (P < 0.05). The intestine and IPF showed relatively higher correlation. On the other hand, the control group had the lowest tissue‐diet correlation, followed by the LA/LNA0.53 group (P < 0.05), whereas the LA/LNA2.09 showed the highest. The LA/LNA ratios in the tissues were up‐regulated in the LA/LNA0.53, 1.04 groups and down‐regulated in the LA/LNA3.95, 6.82 groups. This was due to when LA (or LNA) was highly added in diet, the decrease in this FA was huge in tissue. The contents of saturated fatty acids and monounsaturated fatty acids increased in the control group, but seemed not influenced by dietary LA/LNA ratios. These results demonstrated that the FA deposition was tissue‐specific, and also influenced by the dietary FA composition in the experimental fish. Finally, we suggest that 2.09 is the optimal LA/LNA ratio (2% C₁₈ PUFA) of Songpu mirror carp for fillet FA composition.     

Dietary ratios of n‐3/n‐6 fatty acids do not affect growth of Nile tilapia at optimal temperatures (28°C) nor at temperatures that simulate the onset of winter (22°C)

Nile tilapia (Oreochromis niloticus) juveniles were fed diets containing 13 g/kg total polyunsaturated fatty acids (PUFAs) at different n‐3/n‐6 dietary ratios (0.2, 0.5, 0.8, 1.3 and 2.9) for 56 days, at 28°C. Subsequently, fish were submitted to a winter‐onset simulation (22°C) for 33 days. PUFA n‐3/n‐6 dietary ratios did not affect fish growth at either temperature. At 28°C, tilapia body fat composition increased with decreasing dietary PUFA n‐3/n‐6. Winter‐onset simulation significantly changed feed intake. The lowest dietary n‐3/n‐6 ratio resulted in the highest feed intake. At both temperatures, body concentrations of α‐linolenic acid, docosahexaenoic acid, eicosatrienoic acid and docosapentaenoic acid decreased as dietary n‐3/n‐6 decreased. Body concentrations of eicosapentaenoic acid (EPA, 20:5 n‐3) increased with decreasing concentrations of dietary EPA. The n‐6 fatty acids with the highest concentrations in tilapia bodies were linoleic acid and arachidonic acid (ARA, 20:4 n‐6). At 28°C, SREBP1 gene expression was upregulated in tilapia fed the lowest n‐3/n‐6 diet compared to tilapia fed the highest n‐3/n‐6 ratio diet. Our results demonstrate that a dietary PUFA of 13 g/kg, regardless of the n‐3/n‐6 ratio, can promote weight gains of 2.65 g/fish per day at 28°C and 2.35 g/fish per day at 22°C.     

Effects of varying dietary fatty acid profile on growth performance, fatty acid, body and tissue composition of juvenile pike perch (Sander lucioperca)

Pike perch (Sander lucioperca) has been identified as specie destined to diverse European inland aquaculture, but knowledge on the nutritional requirements is weak. Therefore, we investigated the effect of varying dietary fatty acid (FA) profile by partial replacement of fish oil (FO) with vegetable oils on growth, FA and body composition of juvenile pike perch. An extruded basal diet containing 59 g kg^?1 crude lipids (FO) was added with 60 g kg^?1 FO, 60 g kg^?1 linseed oil (LO) or 60 g kg^?1 soybean oil (SO). The resulting dietary FA composition differed mainly in the triglyceride fraction and was characterized by highest amounts of linolenic acid (18:3 n‐3) in the LO diet and linoleic acid in the SO diet. Diet enriched with FO contained highest contents of highly unsaturated FA 20:5 n‐3 (eicosapentaenic acid) and 22:6 n‐3 (docosahexaenic acid). Pike perch were held in a recirculation system and each feeding group (in triplicate) was fed with experimental diets at a daily rate of 35 g kg^?1 of biomass for 57 days by automatic feeders. Weight gain and specific growth rate of experimental feeding groups ranged between 18.47 and 19.58 g and 1.37–1.45% day^?1 and was not affected by the dietary composition indicating that FO can be replaced by vegetable oils without negative impact on growth performance. In contrast to the whole body and muscle composition, liver tissue was affected by the varying diets. Liver tissues of fish fed diets enriched with vegetable oils showed significantly increased lipid contents of 162 (LO) and 147 (SO) g kg^?1 and indicate decreased lipid utilization compared with fish fed FO diet (liver lipid content 112 g kg^?1). Nevertheless, hepatosomatic index of pike perch was not influenced by dietary lipid composition. The FA profile of pike perch was generally determined by the dietary FAs.     

Influence of 18:2n‐6/20:5n‐3 ratio in diets on growth and fatty acid composition of juvenile abalone,Haliotis discus hannai Ino

A 120‐day feeding trial was conducted to examine the effects of the ratio of dietary linoleic acid (LA, 18:2n‐6) to eicosapentaenoic acid (EPA, 20:5n‐3) on the growth and fatty acid composition of juvenile Haliotis discus hannai (initial shell length 10.23 ± 1.48 mm; initial body weight 0.13 ± 0.05 g) in a recirculation water system. Five semipurified diets with 35 g kg^?1 total lipid were formulated to contain graded LA/EPA ratios (1 : 0, 0.75 : 0.25, 0.5 : 0.5, 0.25 : 0.75, and 0 : 1, respectively). Twenty‐five juveniles were stocked in a rearing unit, a plastic basket (20 × 20 × 10 cm), as a replicate, and there were three replicates for each dietary treatment. The results showed that abalone survival rates were generally high (90.1–98.3%) and independent of the dietary treatments. However, abalone growth was significantly affected by LA/EPA ratio (P < 0.05). The LA/EPA ratio of 0.25 : 0.75 (Diet 4) produced the highest weight gain rate (WGR, 416.3%), closely followed by the ratio of 0 : 1 (Diet 5, 412.9%), the ratio of 0.5 : 0.5 (Diet 3, 399.7%) and the ratio of 0.75 : 0.25 (Diet 2, 372.1%), but no significant differences were observed among these treatments. The abalone fed the diet without 20:5n‐3 (Diet 1) had the lowest WGR (Diet 1, 363.8%), which was significantly lower than that of Diet 4. Fatty acid profiles in abalone body reflected those of dietary lipids, especially for the polyunsaturated fatty acids. The contents of arachidonic acid (AA; 20:4n‐6) in abalone tissues were positively correlated with dietary level of 18:2n‐6 (P < 0.05). Similar correlation was also observed between the level of docosahexaenoic acid (DHA, 22:6n‐3) in abalone tissues and the level of dietary EPA. It is suggested that abalone, H. discus hannai, have the capacity to synthesize 20:4n‐6 from 18:2n‐6, and maybe 22:6n‐3 from 20:5n‐3.     

High dietary 18:2n‐6/18:3n‐3 ratio does not inhibit elongation and desaturation of 18:3n‐3 to EPA and DHA in Atlantic salmon (Salmo salar L.)

This study investigated whether retention of n‐3 fatty acids (FAs) is influenced by the levels of dietary monounsaturated (MUFA)‐, saturated (SFA)‐ and n‐6 FAs. The feeding trial used a mixture design, with rapeseed‐, palm (PO)‐ and soybean oil (SO), providing high levels of MUFA, SFA and n‐6 FAs, respectively, while 18:3n‐3, eicosapentaenoic acid (20:5n‐3) and docosahexaenoic acid (DHA, 22:6n‐3) were kept constant. Furthermore, a diet group with high SO and reduced 18:3n‐3 was included in addition to the mixture design. There were no differences in growth or proximate composition, but the PO diet gave reduced FA digestibility and increased feed conversion ratio. All diet groups had a net production of DHA, shown by retention values >100% (133%–177%). High dietary n‐6 FAs of up to 43% of FAs (18:2n‐6/18:3n‐3 ratio 8.6) did not negatively affect DHA retention, but rather had a small positive impact. High levels of substrate (dietary 18:3n‐3 at ~10% of FAs) did not enhance DHA retention compared to 5% 18:3n‐3. This is a highly significant finding for the aquaculture industry, allowing for greater flexibility in the choice of lipid sources to replace fish oil in salmon feeds.     

Effects of dietary n‐3 to n‐6 fatty acid ratios on spawning performance and larval quality in tongue sole Cynoglossus semilaevis

This study investigated the effect of n‐3 to n‐6 fatty acid ratios in broodstock diets on reproduction performance, fatty acid composition of eggs and gonads of tongue sole Cynoglossus semilaevis. Broodstock were fed five isonitrogenous and isoenergetic diets for 60 days. The supplemented lipids were prepared by a combination of fish oil and soybean oil inclusion FO (fish oil); FSO1 (fish oil: soybean oil = 7:1); FSO2 (fish oil: soybean oil = 2.2:1); FSO3 (fish oil: soybean oil = 1:1); FSO4 (fish oil: soybean oil = 1:4.3) as lipid sources with different n‐3 to n‐6 fatty acid ratios 10.40, 5.21, 2.81, 1.71 and 0.87. Results showed that relative fecundity, fertilization rate and survival rate of larvae at 7 days posthatching were all higher in broodstock fed FSO1 and FSO2 diet and significantly (P < 0.05) decreased in groups fed FSO3 and FSO4 diets. The best result in starvation tolerance test was obtained in FSO2 diet. The present study suggests that n‐3 and n‐6 PUFA ratio in broodstock diet has a considerable effect on spawning performance, egg and larval quality for C. semilaevis.     

Effects of dietary docosahexaenoic acid (22:6n‐3) and arachidonic acid (20:4n‐6) on the growth,survival, stress resistance and fatty acid composition in black sea bass Centropristis striata (Linnaeus 1758) larvae

The objectives of this study were to determine the effects of the dietary docosahexaenoic acid (DHA) to arachidonic acid (ARA) ratio on the survival, growth, hypersaline stress resistance and tissue composition of black sea bass larvae raised from first feeding to metamorphic stages. Larvae were fed enriched rotifers Brachionus rotundiformis and Artemia nauplii containing two levels of DHA (0% and 10% total fatty acids=TFA) in conjunction with three levels of ARA (0%, 3% and 6% TFA). On d24ph, larvae fed the 10:6 (DHA:ARA) treatment showed significantly (P<0.05) higher survival (62.3%) than larvae fed 0:0 (DHA:ARA) (27.4%). Notochord length and dry weight were also significantly (P<0.05) greater in the 10:6 (DHA:ARA) treatment (8.65 mm, 2.14 mg) than in the 0:0 (DHA:ARA) (7.7 mm, 1.65 mg) treatment. During hypersaline (65 g L⁻¹) challenge, no significant differences (P>0.05) were observed in the median survival time (ST50) between larvae fed 10% DHA (ST50=25.6 min) and larvae fed 0% DHA (ST50=18.2 min). The results suggested that black sea bass larvae fed prey containing 10% DHA with increasing ARA within the range of 0–6% showed improved growth and survival from first feeding through metamorphic stages.     

Effects of dietary n‐3 PUFA supplements on composition of n‐3 PUFA and expression of fatty acid elongase 5 (AJELOVL5) in sea cucumber,Apostichopus japonicus

This is the first comprehensive study on the effect of dietary polyunsaturated fatty acid (PUFA) levels on the expression of fatty acid elongase 5 (AJELOVL5), PUFA composition, and growth in juvenile sea cucumbers. The specific growth rate (SGR_w) was improved in n‐3 PUFA‐rich diets compared to low n‐3 PUFA diets. AJELOVL5 expression was apparently upregulated in juveniles fed lower PUFA diets relative to higher PUFA diets, with higher expression in the body wall and respiratory tree of juveniles fed diets without ɑ‐linolenic acid (ALA, 18:3n‐3) compared to juveniles fed higher ALA level diets; similar results were also detected in juveniles fed diets with lower eicosapentaenoic acid (EPA, 20:5n‐3), docosahexaenoic acid (DHA, 22:6n‐3), and none of ALA, EPA, or DHA respectively. The concentrations of ALA, EPA, and DHA in tissues were positively related to the content of dietary corresponding PUFA, with higher ALA content in juveniles fed diet ALA_12.71 than in the ALA_7.46 and ALA₀ groups. Similar results were also obtained in sea cucumber fed diets enriched with either EPA or DHA. Interestingly, considerable levels of EPA and DHA were found in the tissues of juveniles fed diets of CK₀ and DHA₀, with no specific input of EPA or DHA, showing that the sea cucumber was capable of biosynthesizing EPA and DHA from their corresponding precursors as ALA and linoleic acid (LA, 18:2n‐6).     

Changes in lipid content, fatty acid composition and lipid class composition of eggs and developing larvae (0–40 days old) of cultured common dentex (Dentex dentex Linnaeus 1758)

Total lipid content, fatty acid (FA) composition and lipid class composition of common dentex eggs spawned at different times and larvae reared under different culture conditions until 40 days posthatch (dph) were analysed to get a general pattern of lipid composition during larval development. Two groups of larvae were kept under starvation to compare their FA composition with that obtained from normally fed larvae. To compare FA use or accumulation during larval development, results were grouped according to the developmental stage of the larvae instead of age in days posthatch. Saturated and monounsaturated FAs decreased along larval development, while polyunsaturated fatty acid (PUFA) content increased. The ratio of docosahexaenoic acid (DHA)/eicosapentaenoic acid shifted from 4 to 5 in early developmental stages to lower than 1 after metamorphosis. Arachidonic acid levels remained constant along larval development. Larvae kept 6 days under starvation consumed most of their n-3 PUFA while conserving the DHA to values at day 0. The results presented here are useful for the design of nutritional experiments, because there were differences detected in terms of lipid and FA composition between developmental stages with higher differences mainly found in first-feeding larvae and early developmental stages.     

Fine‐scale movement ecology of a freshwater top predator,Eurasian perch (Perca fluviatilis), in response to the abiotic environment over the course of a year

Fine‐scale underwater telemetry affords an unprecedented opportunity to understand how aquatic animals respond to environmental changes. We investigated the movement patterns of an aquatic top predator, Eurasian perch (Perca fluviatilis), using a three‐dimensional acoustic telemetry system installed in Kleiner Döllnsee (25 ha), a small, shallow, mesotrophic natural lake. Adult piscivorous perch (N = 16) were tagged and tracked in the whole lake at a minimum of 9‐s intervals over the course of one year. Perch increased swimming activity with higher water temperature and light intensity. Air pressure, wind speed and lunar phase also explained perch movements, but the effects were substantially smaller compared to temperature and light. Perch showed a strong diel pattern in activity, with farther swimming distances and larger activity spaces during the daytime, compared to the night‐time. To investigate the influence of prey distribution, we sampled the prey fish in both littoral and pelagic zones in both day and night monthly using gill nets. We found that the prey fish underwent diel horizontal migration, using the littoral zone during the day and the pelagic zone during the night. However, perch showed the opposite patterns, suggesting either that the prey fish avoided predation risk or that the horizontal diel migration of perch was driven by other mechanisms. Our results collectively suggest that the movement ecology of piscivorous perch is mainly governed by a foraging motivation as a function of abiotic variables, especially temperature and light.