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Insect meals are considered among the most promising feed materials in fish nutrition due to their sustainability and possibility of fish meal replacement. The present study is the first application of full-fat black soldier fly larvae (BSFL) meal in brown trout (Salmo trutta m. fario) diets. Two experiments were performed on 240 brown trout fingerlings (average body mass 4.85 g) distributed into four groups (12 tanks for the growth performance experiment, 10 fish/tank; and 12 metabolic tanks for the digestibility test, 10 fish/tank). The experimental group design was conducted as follows: control diet, with no BSFL and 35% fish meal, and experimental diets: BSFL5 – with 5% BSFL full-fat meal and 32.5% fish meal; BSFL10 – with 10% BSFL full-fat meal and 30% fish meal; and BSFL20 – with 20% BSFL full-fat meal and 25% fish meal. No effects were recorded in the case of growth performance and feed utilization parameters. The environmental sustainability of the usage of insect meals in fish diets was proven – due to the lower fish meal inclusion, the fish-in-fish-out ratio decreased by 31% in BSFL20. In the case of the viscerosomatic index, increases in BSFL5 and BSFL20 were reported. In all experimental groups, decreases in hepatosomatic index values were observed. Crude protein digestibility decreased in BSFL5 and BSFL20, while crude fat digestibility decreased only in the BSFL20 group. The effect of including BSFL full-fat meal in a brown trout diet on serum biochemical parameters was reported. The aspartate transaminase concentration increased in BSFL10 and BSFL20, while the gamma-glutamyl transpeptidase values decreased in BSFL20. In the case of total cholesterol, higher values were observed in BSFL10 and BSFL20. The albumin content decreased in the BSFL20 group, while globulin showed the highest values in the control group. The microbiota composition was not affected by insect meal inclusion. In conclusion, the results of the present study showed the high potential of BSFL full-fat meal application of up to 20% in a brown trout diet.

The results are based on two experimental high-manganese X98MnAlSiNbTi24-11 and X105MnAlSi24-11 steels subjected to thermo-mechanical treatment by hot-rolling on a semi-industrial processing line. The paper presents the results of diffraction and structural studies using scanning and transmission electron microscopy showing the role of Nb and Ti micro-additives in shaping high strength properties of high-manganese austenitic-ferritic steels with complex carbides. The performed investigations of two experimental steels allow to explain how the change cooling conditions after thermo-mechanical treatment of the analysed steels affects the change of their microstructure and mechanical properties. The obtained results allow assessing the impact of both the chemical composition and the applied thermo-mechanical treatment technology on the structural effects of strengthening of the newly developed steels.

The paper presents the results of the effect of isothermal heating time on the disappearance of strain hardening (the softening degree) of the studied high-manganese TRIPLEX type steels at a temperature of 900 and 1000°C. In order to determine the kinetics of recrystallization of austenite plastically deformed for selected steels, hot compression tests with draft ε = 0.2 were made. The presented results reveal that the complete recrystallization of austenite needs long isothermal heating times. In industrial conditions, such long times are not used, therefore in the initial rolling passages, the time required for half recrystallization of austenite t0.5 is often used. The total disappearance of the strain hardening, completion of the recrystallization of austenite tested high-manganese X98 and X105 TRIPLEX type steels isothermal heating time requires far more than 200 s. The increase of the deformation temperature is a factor influencing the acceleration of the disappearance of strain hardening.

Background. Development of modern aquaculture and the increasing consumer demand provoke improvements in the complex breeding technologies of economically valuable fish species. Wels catfish, Silurus glanis L. (known also as the European catfish), because of its breeding and consumption values, becomes an increasingly common object of breeding. The objective of the presented work was the evaluation of selected feeds differing in dietary lipids levels applied in rearing the wels catfish fry under controlled conditions. Materials and methods. The feeding trial (60 days) was carried out with the wels catfish fry, weighing on average 55 g. The experiment was conducted under controlled conditions in an aquarium hall in 60-L flow-through tanks. During the growth test, the fish were given four commercial feeds of the same protein amount (45%) and graded fat levels (15%, 20%, 25%, and 30%). In the final evaluation of the feeding tests, the following rearing effectiveness indices were used: food conversion ratio (FCR), specific growth rate (SGR), protein efficiency ratio (PER), protein retention (PR), lipid retention (LR), and survival rate (SR). Conclusions were drawn on the basis of statistical analysis using Statistica computer software. Results. The wels catfish fed 20%-fat-content feed attained the highest individual weights. The other treatments yielded statistically significantly lower (P < 0.05) body weights. No statistically significant differences were found between the mean values of the specific growth rate (SGR). The values of feed conversion ratio (FCR) and protein efficiency ratio (PER) were approximately equal in the individual groups. The protein retention attained values from 28.2% to 33.0%, while fat retention ranged from 11.8% to 24.2%. No mortalities were recorded. The amount of fat in all groups increased significantly after the termination of the growth. The increase of fat amount in the feed was not correlated with the growth of fat amount in the fish body. The levels of the other body components increased, but no differences between the groups were found. Conclusion. Differentiated amounts of dietary lipids in the diet did not exert any effect on the rate of fish growth or on the proper utilization of the nutritive components in feeds.

Background. Constant improvement of animal feed formulas calls for new raw materials. In the feeding of fish, one of diet recipe optimization methods is to search for feed protein sources alternative to fish meal. The presently reported study focuses on an unconventional protein source—the erythrocyte meal—for feeding fry of common carp. Materials and methods. The barothermal method (extrusion) was applied for the formulation of experimental feeds prepared as isonitrogenous and isocaloric diets. In the feeds tested, the erythrocyte meal was used as fish meal substitutes at different substitution levels (control diet C = 0%, E5 diet = 5%, E10 diet = 10%, and E15 diet = 15%). The feeds were evaluated on the basis of their physical and chemical characteristics. The feeding trial was carried out on the fry of carp (3.8 ± 0.1 g). The experiments were carried out under controlled conditions in an indoor fish tank facility in twelve 60-L flow-through aquaria. Each aquarium was stocked with 14 fish. In the final evaluation of the feeding tests, the following rearing effectiveness indices were used: food conversion ratio (FCR), specific growth rate (SGR), protein efficiency ratio (PER), and survival rate (SR). The data obtained were statistically processed using Statistica computer software. Results. At the end of the experiment, the fish body weight from treatment C was significantly (P < 0.05) higher than the weights of treatments E5 and E15. Significant body weight differences occurred also between treatments E5 and E15. Values of specific growth rate (SGR) depended on the type of applied feed. The minimal value (1.86% • d-1) was reached in treatment E15, while the maximal value (3.34% • d-1) was recorded in treatment C. The most favourable FCR and PER values were recorded for C feed and they differed significantly from the values obtained with other experimental feeds. The application of experimental feeds to carp resulted in an increase in dry matter content in all treatments, and total protein and fat in the fish bodies from groups C and E5. However, there was no change in body ash content at feeding trial. Conclusion. Experimental results showed that the erythrocyte meal addition at 5%, 10%, and 15% rate as replacement for 15% of fish meal did not improve the rearing parameters of common carp fry.

Four isonitrogenous (gross protein content 32%) and isoenergetic (gross energy content 4 080 kcal/kg) diets were prepared by extrusion to investigate the effects of different cereal grains (barley - diet A, wheat - diet B, triticale - diet C, rye - diet D) as carbohydrate compounds of extruded feeds for carp. The physical and chemical properties of the feeds were established. A 60-day growth test was performed in experimental ponds of 40 m2 area. Each diet was fed to three groups of fish (initial average weight 200 ± 10 g). The following rearing effectiveness indices were used in the final evaluation of the growth test: weight gain (WG, %), specific growth rate (SGR, %/d), food conversion ratio (FCR), protein efficiency ratio (PER) and protein retention (PR, %). Conclusions were based on statistical analysis using the Statistica 5.0 package. The results obtained in the growth test did not show any differences in the evaluated feeds regarding their usefulness in the nutrition of carp (there were no statistically significant differences in the values of fish rearing parameters, P ≤ 0.05). The recorded growth parameters of carp were as follows: WG: 308.48-324.0%; SGR: 2.81-2.92%/d; the feed conversion coefficients were: FCR: 1.43-1.50; PER: 1.75-1.83; PR: 29.54-31.72%.

The aim of the experiment was to determine the effect of graded lipid content in experimental isoprotein feed (6, 10, 14% lipids and 45% protein) on the growth performance of juvenile pikeperch (initial body weight P < 0.05). Feed conversion ratio (FCR) and protein efficiency ratio (PER) attained the most advantageous values in this group of fish. The application of the experimental feed had a significant effect on the lipid values in fish bodies and viscera (P < 0.05) although no relationship was detected between the lipid content of the feed and that of the fish muscles. The lipid content was approximately 7.7% in all the experimental groups and the differences between the groups were statistically insignificant (P > 0.05).