Development of some digestive enzymes in Eurasian perch larvae Perca fluviatilis

The activities of some digestive enzymes were investigated in Eurasian perch Perca fluviatilis larvae fed live preys during the first month of life. Activities of pancreatic and intestinal enzymes displayed a pattern characteristic of developing animals. Pancreatic enzymes were efficient at the time of hatching. Trypsin and amylase specific activities increased during the first developmental days, then decreased even though segmental activities increased continuously as the larvae grew. The increase of chymotrypsin specific activity was proportional to fish growth. From day 21 after hatching to the end of experiment, the strong increase in the activities of alkaline phosphatase, leucine-aminopeptidase N, maltase and γ-glutamyl transpeptidase reflected the development of brush border membranes of enterocytes. This phenomenon occurred concurrently with a decrease in a cytosolic enzyme, the leucine-alanine peptidase. These opposite patterns indicate a maturation of enterocytes and the acquisition of an adult mode of digestion within the first month of live. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

The effect of feeding on oxygen consumption and ammonia excretion of juvenile tench Tinca tinca (L.) reared in a water recirculating system

The effect of feeding frequency (one, three, and continuous feeding), feed ration (0.2, 0.5, 0.8% of total fish biomass), and feeding per se on the oxygen consumption (OC, mg O₂ kg⁻¹ h⁻¹) and ammonia excretion (AE, mg TAN kg⁻¹ h⁻¹) of juvenile tench (body weight 15–19 g) and variations in these parameters in daily cycles were examined. Fish metabolism was studied in a recirculating system (rearing tanks of 0.2 m³, water temperature 23 °C). It was found that oxygen consumption and ammonia excretion depended significantly on feed ration. An increase of feed ration from 0.2 to 0.8% of fish biomass caused an increase of OC and AE from 126.80 mg O₂ kg⁻¹ h⁻¹ and 1.95 mg TAN kg⁻¹ h⁻¹ to 187.35 mg O₂ kg⁻¹ h⁻¹ and 8.80 mg TAN kg⁻¹ h⁻¹ (p<0.05). There was no dependence between feeding frequency and the mean rate of oxygen consumption. However, the relationship between feeding frequency and ammonia excretion by juvenile tench was statistically significant (p<0.05). Feeding frequency significantly affected daily fluctuations of AE and OC. It was found that diurnal variations in metabolic rates were strictly related to tench feeding, and the daily variations of AE were significantly higher than OC.     

温度对黄金鲈(Perca flavescens)耗氧率和排氨率的影响

在不同水温(15、20、25和30℃)下,对体重(46.1±4.5)g黄金鲈(Perca flavescens)的耗氧率和排氨率进行了测定与分析。结果显示:黄金鲈的耗氧率和排氨率均随温度的升高而显著增加(P<0.01);耗氧率和排氨率与温度的关系可用指数方程拟合,其方程分别为:RO=0.0682 e0.0633t,R2=0.9879;RN=2.4593 e0.0904t,R2=0.9703;随着温度的升高氧氮比(O:N)逐渐降低;耗氧Q10值和排氨Q10值均在20~25℃之间最小。结果表明:在各温度水平下黄金鲈基础代谢消耗底物主要均以蛋白质为主,脂肪其次,然而随着温度的升高,黄金鲈利用糖类和脂肪供能的比例逐渐下降,而蛋白质供能的比例逐渐增加。黄金鲈的最适生长温度为20~25℃。     

Early development and allometric growth in hatchery‐reared Eurasian perch,Perca fluviatilis L.

The morphological development and allometric growth patterns of Eurasian perch, Perca fluviatilis L., a highly valued commercial species, were studied under intensive rearing conditions from hatching up to 50 DPH (Days Post Hatch). Based on the external morphology, four different phases during early development of Eurasian perch were identified: pre‐flexion larva 0–20 DPH (5.70–10.16 mm TL); flexion larva 22–30 DPH (11.09–15.14 mm TL) and post‐flexion larva/juvenile 32–50 DPH (18.00–24.75 mm TL). The results indicate that growth period when final replacement of all temporary (larval) structures and most important changes in the shape of P. fluviatilis occurred (between 13.95 and 24.06 mm TL, during flexion and post‐flexion phase) can be considered as a transitional period between the larva and juvenile. All body segments, except trunk length and tail length showed fast growth (positive allometry) throughout the entire studied period or up to the respective inflexion point with a common tendency to isometry. In addition, the specific behaviours (e.g. pelagic way of life) of Eurasian perch larvae resulted in some characteristic allometric growth patterns in the posterior region, different from the majority of other teleosts. The results are discussed with respect to the ontogeny of the functional morphology under both ecological and aquaculture considerations.     

Dynamics of total lipids and fatty acids during embryogenesis and larval development of Eurasian perch (Perca fluviatilis)

Total lipid and fatty acid compositions were determined during embryogenesis and larval development in Eurasian perch (Perca fluviatilis). During embryonic development, perch did not catabolize lipids and fatty acids as an energy source. However, during larval development, there was an exponential relationship between the decrease in total lipids and the duration of starving (r²=0.9957) and feeding (r²=1). The duration of the starving period (10 days post hatching) was shorter than the feeding period (35 days post hatching). In both starved and fed larvae, there is an apparent preference in utilization of polyunsaturated fatty acids followed by monounsaturated fatty acids. Saturated fatty acids were utilized by neither fed perch larvae nor by starved perch larvae. In starved larvae, palmitoleic 16:1(n-7) and oleic 18:1(n-9) acids were the preferentially monounsaturated fatty acids catabolized and their contribution as energy source from total fatty acids catabolized over the first week was 37.6%. In fed larvae, these 2 nutrients were also the most monounsaturated fatty acids utilized as energy source and possibly also as precursors for others monounsaturated fatty acids biosynthesis. During the same period and among (n-6) polyunsaturated fatty acids, starved perch utilized less linoleic 18:2(n-6) and arachidonic 20:4(n-6) acids than fed larvae despite the fact that the starved perch were in more unfavorable nutritional conditions. In the case of (n-3) fatty acids, starved larvae utilized more linolenic acid 18:3(n-3) and less eicosapentaenoic 20:5(n-3) acid and docosahexaenoic 22:6(n-3) acid than fed perch. Starved larvae probably spared 20:5(n-3) and 22:6(n-3) for physiological functions.     

Effects of dietary fat levels on growth, feed efficiency and biochemical compositions of Eurasian perch Perca fluviatilis

A feeding experiment was conducted for 10 weeks with Eurasian perchPerca fluviatilis juveniles (33.1–35.9ginitial body weight) using three dietary fat levels (11.7, 15 and 19.3%). Theresults showed that increasing dietary fat content increased growth, feedefficiency and protein utilization of perch (P < 0.05) but did not affectmortality. Lipid analysis showed that the composition of some perch tissueswerealso significantly affected by increasing dietary fat content, with an increaseof lipid deposition in the viscera (from 64.9% in fish fed 11.7 % fat to 78.8%in fish fed 19.3% fat) and liver (from 12.4 to 23.8%) (P < 0.05), while themuscle composition was not affected by the dietary treament. Highdocosahexaenoic acid (22:6n-3, DHA) and high docosahexaenoicacid/eicosapentoenoic acid (20:5n-3, EPA) ratios were found in the liver andmuscle lipids as compared to the dietary fatty acid compositions, suggestingthat Eurasian perch might possess a high capability of converting the longchainhighly unsaturated fatty acids, especially DHA from its dietary precursors.     

Effects of probiotic bacteria on growth parameters and immune defence in Eurasian perch Perca fluviatilis L. larvae under intensive culture conditions

Two experiments were conducted to examine whether a mixture of bacteria composed of Bacillus licheniformis, Bacillus subtilis and Bacillus pumilus has a beneficial impact on survival, growth, lysozyme activity and total immunoglobulins (Ig) in perch larvae. In experiment 1, control fish were compared with fish receiving bacteria (4.93 × 10⁷ CFU L⁻¹ day⁻¹) through tank water or both through tank water and Artemia metanauplii enriched with two bacteria doses (2 × 10¹⁰ or 4 × 10¹⁰ CFU L⁻¹). Treatments were performed in 40 L triplicate tanks of 200 fish [initial body weight (IBW)=2.3 mg] each, placed in separated recirculating water systems. Experiment 2 evaluated the combining effects of bacteria feeding and densities (10 vs. 20 fish L⁻¹, IBW=9.5 mg). In both experiments, the bacteria added to live food or both live food and water induced higher growth rate at the highest dietary dose and this was associated with higher Ig levels on days 14 and 28. In experiment 2, higher survival was associated to lower type‐2 cannibalism (ingestion of whole prey) at the two dietary bacteria doses, and such positive effect was observed for fish fed bacteria at high density. Bacteria administration through water had no effect on growth and survival. In conclusion, the results show that high dietary concentrations of the mixture of bacteria used have potential stimulating impact on growth, survival, lysozyme activity and total Ig. But, further investigations are needed to demonstrate the optimal doses for emphasizing immune defence status.     

不同规格及不同盐度下毛蚶稚贝耗氧率和排氨率的研究

研究了毛蚶稚贝不同规格及不同盐度下的呼吸和排氨率。结果表明,耗氧率随着盐度的升高而升高,当盐度达到30后开始下降。排氨率也表现出相似的规律,在盐度27后开始下降。同时,O∶N值也随着盐度的升高而升高,在盐度30后开始下降。而中等规格(2·41±0·20mm)稚贝的耗氧率和排氨率要高于其余两种规格稚贝,使得规格和耗氧率及排氨率并不形成完全的负相关。     

Effect of light on oxygen consumption and ammonia excretion in Haliotis discus discus, H. gigantea, H. madaka and their hybrids

Oxygen consumption and ammonia excretion rates of three abalone species, Haliotis discus discus, H. gigantea, H. madaka and their hybrids were measured at 20 °C by incubating for 3 h under dark and light (N = 9–13 for each species and hybrid). Animals were fasted before and during the experiment and measurements were made first under dark followed by light on the next day. The rates increased with the increase in body weight and were higher under light than dark. On average, H. discus discus had higher oxygen consumption (DD; dark = 0.039, light = 0.04 ml/g/h) than H. gigantea (G; D = 0.033, L = 0.036) and H. madaka (M; D = 0.034, L = 0.035); the hybrids had varied patterns with respect to their parental species [DD × M (D = 0.032, L = 0.038); M × DD (D = 0.03, L = 0.038); G × DD (D = 0.035, L = 0.04) and DD × G (D = 0.03, L = 0.034), mother first]. M (0.261, 0.298 μmol/g/h) had the highest ammonia excretion rate while G (0.162; 0.264) and DD (0.229; 0.232) had the lowest under dark and light, respectively. The hybrids had varied patterns in comparison with their parents (DD × M = 0.247, 0.32;M × DD= 0.177, 0.28; DD × G = 0.249, 0.364 and G × DD = 0.116, 0.155). The O/N ratios under both conditions in all species and hybrids indicated that they had carbohydrate dominated metabolism. Results demonstrated physiological variability among the species and hybrids indicating necessity of different strategies for their management and aquaculture.     

饥饿及恢复投喂对刺参生长、耗氧率和排氨率的影响

在水温(16±1)℃、盐度27.6±0.5、pH值7.5~8.3条件下,将体重为(28.47±2.02)g的刺参Apostichopus japonicus分别饥饿0(空白对照)、5、10、15和20d(分别记为T0、T5、T10、T15和T20)后再饱食投喂至40d。实验结果表明,随着饥饿时间的延长,刺参的耗氧率呈急速下降、上升、再下降的变化规律;排氨率呈先上升、后下降的变化规律;氧氮比呈先下降、后上升的变化规律。饥饿结束时刺参的体重,除T5组外,其余各组均显著小于T0组(P0.05),且各自均有不同程度的下降,耗氧率和排氨率与T0组比较均呈显著性差异(P0.05)。饥饿对刺参O/N比值的影响显著(P0.05),饥饿初期刺参O/N比值平均为10左右,随着饥饿时间的延长,刺参O/N比值降为小于7。实验结束时,各饥饿组刺参的体重和特定生长率均小于T0组(P0.05),除T5组外,各组的耗氧率和排氨率,均未能恢复至T0组水平(P0.05)。可见,饥饿后恢复投喂的刺参不具有补偿生长的特征。     

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.     

Prey selection and growth in 0+ Eurasian perch Perca fluviatilis L. in littoral zones of seven temperate lakes

We studied the relationships between the planktonic food base and feeding patterns of juvenile mid-summer/early autumn Eurasian perch Perca fluviatilis L., a common predatory freshwater fish in large parts of Europe and Asia. The feeding of 0+ perch was studied during summer and autumn in littoral habitats of seven lakes with different environmental conditions – four Latvian (Auciema, Riebinu, Vārzgūnes, Laukezers) and three Estonian (Kaiavere, Prossa and Akste) lakes. Simultaneously, the abundance, biomass and structure of zooplankton communities were examined. We focused on the littoral areas because many studies in lakes suggest that littoral habitats are particularly important for 0+ fish growth and survival. We were interested in the question: can the diet and growth of 0+ perch be explained by zooplankton community structure? We also presumed that if the amount of zooplankton is low, more benthic invertebrates will be consumed by 0+ perch. Opposite to expectations, we found that zooplankton always counted for over 90% of diet biomass in perch. There were also clear correlations between the zooplankton biomass in a given lake, the zooplankton biomass in 0+ perch stomachs, and the fish growth rate. The study also suggested that nutrient enrichment can positively impact the 0+ perch feeding conditions in lakes.     

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.     

Weaning of juvenile pikeperch, Stizostedion lucioperca L., and perch, Perca fluviatilis L., to formulated feed

Weaning success of pond‐cultured pikeperch and wild‐caught perch (mean length 51 and 48 mm respectively) was evaluated using different weaning techniques and different formulated feeds. Juveniles that were fed formulated feed grew as well as or better than juveniles that were weaned successively using zooplankton or yolk. Four different formulated feeds (agglomerated marine larvae feed, marine larvae feed, trout feed and a semi‐moist feed) were evaluated regarding specific growth rate (SGR), condition factor and a subjective stomach fullness estimate. The agglomerated marine larvae feed gave significantly better weaning performance than the other feeds regarding all parameters (SGR = 7.3% day^?1 and 3.4% day^?1 for pikeperch and perch respectively).     

Identification of bacteria from the normal flora of perch, Perca fluviatilis L., and evaluation of their inhibitory potential towards Aeromonas species

Pathogenic Aeromonas sobria has been identified as a causative agent of ulcerative disease in farmed European perch, Perca fluviatilis L. To study the effect of the normal intestinal bacterial flora of perch against A. sobria, we sampled 193 bacterial isolates from the perch digestive tract. The isolates were identified by sequence analysis of the 16S rRNA gene and their inhibitory potential against A. sobria was evaluated in vitro. Nineteen of the strains isolated showed inhibition and were also tested against other aeromonad and non-aeromonad fish pathogens including Yersinia ruckeri and Vibrio anguillarum. Isolates showing inhibition were primarily Pseudomonas spp.; however, inhibitory Shewanella spp., and Delftia sp. were also identified. A Pseudomonas chlororaphis isolate showed inhibition against all fish pathogens tested.     

Composition of the microbial communities in the gastrointestinal tract of perch (Perca fluviatilis L. 1758) and cestodes parasitizing the perch digestive tract

Using the approach of sequencing the V3-V4 region of the 16S rRNA gene, we have analysed the bacterial diversity associated with the distinct compartments of the gastrointestinal tract of perch (Perca fluviatilis) and cestodes (Proteocephalus sp.) parasitizing their digestive tract. The dominant microbiota associated with cestodes (Proteocephalus sp.) was represented by bacteria from the genera Serratia, Pseudomonas and Mycoplasma. By comparing the associated microbiota of perch and cestodes, a clear difference in bacterial composition and diversity was revealed between the community from the stomach content and other parts of the gastrointestinal tract of fish. Microbiota associated with cestodes was not significantly different in comparison with microbiota of different subcompartments of perch (mucosa and content of intestine and pyloric caeca) (ADONIS, p > .05) excluding microbiota of stomach content (ADONIS, p ≤ .05). PICRUSt-based functional assessments of the microbial communities of perch and cestodes indicated that they mainly linked in terms of metabolism and environmental information processing and could play an important role in the nutrition and health of host.