The effectiveness of using the microbial synthesis protein "Gaprin" in feeding juvenile Australian red-clawed crayfish

. In the conditions of the scientific center “Breeding valuable breeds of sturgeon” of the Volgograd State Agrarian University, the effectiveness of replacing 75% of fishmeal in the feed for juvenile Australian red claw crayfish with microbial protein - haprin has been experimentally proven. The influence of experimental feeds on weight gain, linear indicators and survival of individuals was studied, and their economic efficiency was determined. Practical recommendations have been developed to allow the implementation of the developed recipe at aquaculture enterprises containing Australian red-claw crayfish.


Introduction
Currently, the Australian red claw crayfish (Cherax quadricarinatus) is a subject of aquaculture.This tropical species, unpretentious to food, is well adapted for industrial breeding -in the 7th month of keeping the weight of individual individuals reaches 90 g, which is a commercial weight, and in 1.5 years -200 g, with a total content of muscle tissue in the body of up to 36%.
It is known that the most effective for Australian crayfish are feeds with a protein content of 20-30% and a low fat content -up to 8%.Juveniles are more demanding of high protein content.For its rapid growth, formulations at a level of 30-35% are required.When feeding crayfish, as a rule, they use food intended for other aquatic organisms -usually shrimp, salmon or catfish food.The lack of recipes for specialized feeds for crustaceans, the need for high-protein formulations, as well as the low return on investment in biotechnology for breeding crayfish, leads to the need to develop special low-cost feeds.
The substance gaprin is a product of microbiological synthesis and an important protein feed additive that can significantly improve the quality of nutrition and ensure the growth of aquatic organisms.However, to date, the effectiveness the introduction of haprin into crustacean feeds has not been sufficiently studied.This justifies the scientific and practical interest of testing new high-protein, low-cost feed formulations for crustacean aquaculture.

Materials and methods
The research was carried out at the scientific center "Breeding valuable sturgeon breeds" of the Volgograd State Agrarian University, in January-February 2023.The objects of the study were juveniles of the Australian red-clawed crayfish (Cherax quadricarinatus).The research hypothesis is that the product of microbial synthesis, gaprin, should positively influence the dynamics of growth, development and survival of cancer populations.For the experiment, three groups of juvenile Australian red-clawed crayfish were created, the same age (3.5 months) and weight (6.17 ± 0.08 years).The number of each group was 30, all individuals were in the same environmental conditions -in the pools of the RAS system of the scientific center.
The study was carried out using standard zootechnical experience -the method of comparing the control and experimental groups and further assessing their productive qualities.Experiment scheme: the control group was fed standard trout feed, the 1st experimental group was fed an experimental feed with 50% of fishmeal replaced by gaprin, the 2nd experimental group was given food containing 75% replacement of fishmeal with gaprin.The feeding rate was 2% of the total biomass.The food was weighed on a scale before each feeding.
Control measurements of live weight and linear parameters in juvenile crayfish were carried out every 10 days: the livestock was recalculated and weighed on electronic scales; The total length of the individual was measured from linear indicators: from the tip of the claws to the end of the telson plates.

Results
The results of the experiment, based on the dynamics of growth in the average weight of juvenile Australian red-clawed crayfish, are reflected in Table 1.Analyzing the data in Table 1, the most significant increase in juveniles was observed in experimental group No. 2 -9.7 g, against 9.3 g in group 1 and 8.7 g in the control.At the first measurement, the growth of juveniles of the control group increased by 0.97 g (15.7%), experimental group No. 1 by 1.2 g (18.9%), experimental group No. 2 by 0.8 g (12.4 %).At the second measurement, the growth of juveniles of the control group increased by 0.8 g (11.5%), experimental group No. 1 by 0.7 g (9.7%), experimental group No. 2 by 1.4 g (20.5% ).At the final measurement, the growth of juveniles of the control group increased by 0.69 g (8.7%), experimental group No. 1 by 1.2 g (14.8%), experimental group No. 2 by 1.5 g (18.3% ).
The values of the absolute increase in the total live weight of the studied groups are given in Table 2. Analyzing the data in Table 2, we can note a decrease in the absolute increase in total live weight in experimental groups 1 and 2. It was noted that during the first measurement, the absolute increase in live weight of juveniles in the control group increased by 15 g (8.1%), in experimental group No. 1 by 13 g (7.0%), experimental group No. 2 by 9 g (5%).At the second measurement, this indicator for the control group decreased by 1.1 g (0.6%), experimental group No. 1 by 13 g (6.5%).The values for experimental group No. 2 increased by 14.5 g (7.6%).At the final measurement, the absolute increase in the total live weight of juveniles of the control group decreased by 8.7 g (4.4%), experimental group No. 1 by 19 g (10.2%), experimental group No. 2 by 30.5 g (14.8%).These results on the total mass of individuals of the groups are due to the better safety of the livestock of the control group.This circumstance has the following dependence -the best growth in the experimental groups was due to more frequent molting, and it is known that during the molting period individuals are most vulnerable to cannibalism.Thus, due to the high mortality rate during the experiment, individuals from the experimental groups received a lower total mass as a result of the experiment.
Data on the dynamics of body length of juvenile Australian red-clawed crayfish are shown in Table 3. From Table 3 it is noticeable that the most significant increase in linear indicator was observed in experimental group No. 2 -10.4 cm (using food with 75% replacement of flour with fish by Gaprin), versus 10.1 cm (in the group with 50% replacement of Gaprin with fish flour).The lowest indicator is 9.9 cm for the control.At the first measurement, the linear indicator of individuals in the control group increased by 0.3 cm (4.1%), experimental group No. 1 by 0.4 cm (4.8%), experimental group No. 2 by 0.9 cm (11.9 %).At the second measurement, the linear indicator of an individual in the control group The results on the survival of juvenile Australian red-clawed crayfish are shown in Table 4.
Analyzing the data in Table 4, the greatest death of individuals was observed in experimental groups No. 1 and No. 2. During the experiment, the control group lost 8 individuals (27%), experimental group No. 1 lost 12 individuals (40%), and experimental group No. 2 also lost 12 individuals (40%).In addition to zootechnical ones, economic indicators were also analyzed during the experiment; the data are presented in Table 5. Analyzing the data in Table 5, it was revealed that in experimental groups 1 and 2 there were lower feed costs per 1 kg of live weight gain -compared to the control.It was noted that costs were 1.7 kg for the control group, compared to 1.4 and 1.2 kg for experimental groups 1 and 2, respectively.Which is less by 0.3 kg (18.6%) and 0.6 kg (32.6%).
In terms of the cost of 1 kg of live weight, the lowest values among the studied groups were noted in the 2nd experimental group -1699 rubles, which is less than the indicator of the 1st experimental group by 69 rubles (4.1%), and by 280 rubles (16.5% ) less than the control.Analyzing the estimated profit from the sale of 1 kg of live weight of crayfish, the highest result was observed in individuals consuming feed with 75% replacement of fishmeal with gaprin (experimental group 2).The profit from the sale of individuals of this group is 69 rubles (16%) more than the value of experimental group 1 (16%) and 280 rubles (126%) more than the control group.
The level of expected profitability is also the highest in experimental group 2 -29.5%, which is higher than the values of experimental group No. 1 and control by 5.1% and 18.3%, respectively.

Discussion
 According to the indicator "dynamics of growth of the average weight" of juvenile Australian red-clawed crayfish, a predominance of the 2nd experimental group was revealed (using feed with 75% gaprin instead of fishmeal) by 9.7 g.  The results for the total weight of the livestock had better values in the control group.
Due to the fact that the best growth in the experimental groups was due to more frequent molting, and during the molting period individuals are most vulnerable to cannibalism.Therefore, during the period of the experiment, individuals from the experimental groups had more waste and, as a consequence, a lower total mass as a result. The most significant linear increase -10.4 cm -was also observed in experimental group No. 2 (75% replacement of fish meal with gaprin). Economic efficiency data also showed an absolute advantage of the 2nd experimental group (75% replacement of fish meal with gaprin) in all studied parameters.

Conclusion
Based on the data of the experiment, it was revealed that replacing 75% of fishmeal with a microbiological synthesis product -gaprin, in the trout feed formulation is a reasonable solution for feeding the aquaculture of Australian red claw crayfish.This feed composition satisfies all the nutritional needs of juvenile crayfish and has a positive effect on their growth and development.
Recommendations for aquaculture establishments holding juvenile Australian red claw crayfish:  The results of the experiment showed the possibility of feeding juvenile Australian red claw crayfish with salmon feed with 75% replacement of fish meal with the product of microbiological synthesis, gaprin.This recipe provides increased growth rates of individuals and, accordingly, more efficient economic indicators of production. It is recommended to carefully monitor the molting processes during the period of growth of the livestock -when changing the old chitinous cover, place individuals in separate containers until the stage of complete formation of a new carapace. It is also recommended to equip pools with shelters in sufficient quantities for the required number of individuals, in order to increase the safety of the livestock.

Table 1 .
Dynamics of the average sample of juveniles of the Australian red-clawed crayfish during the study period, g.

Table 2 .
Dynamics of absolute increase in the total live weight of juvenile Australian red-clawed crayfish, g.

Table 3 .
Dynamics of body length of juvenile Australian red-clawed crayfish, cm.

Table 4 .
Safety of the population of groups of juvenile Australian red-clawed crayfish, pcs..

Table 5 .
Indicators of economic efficiency of growing Australian red claw crayfish using experimental feed formulations.