Physiological and biochemical adaptation indicators of the Azov sea roach Rutilus rutilus (L.) at various stages of its life cycle

Abstract

The roach, inhabiting the Azov Sea, is a semi-anadromous form of the species Rutilus rutilus (L., 1758) that holds major commercial importance. This study has been aimed at the investigation of long-term dynamics exhibited by some characteristics of metabolic activity in roach. The samples for various stages of its life cycle, including spawning, fattening, and wintering states, have been collected during sea trips, through catches of coastal stationary seines in various areas of the Azov Sea, and upon the breeders approaching to the spawning and rearing farms (hatcheries) of the Azov-Kuban Region. Around 3000 matured roach indaviduals aged 3-5 years have been investigated. Average long-term and reference intervals have been established, which limited 80% of the sample; the content of moisture, protein and total lipids in the tissues and organs of roach, as well as protein, cholesterol and lipids in blood, and the elements indicating its trophic quality has been identified. Table 1 shows the results obtained for determining the content of protein and lipids in gonads, liver and muscles, protein, cholesterol and lipids in blood serum. The data are presented in the form of a mean and a mean error (M ± mM). We found out that the investigated characteristics have high variability showing seasonal dynamics and associated with metabolic features of fish individuals with the gonad differing in maturity. During the fattening season that covers the end of spring, summer and autumn, the synthesis of lipids and protein and their deposition in muscle tissue and liver is taking place, their content in blood serum increases, and after this, a relatively fast gonadogenesis begins. Wintering starts with the developed reproductive products at the 4th maturity stage in females and at the 3rd-4th maturity stage in males. After winter depletion of depot fat used for maintaining catabolism and formative processes, their further reduction ensues. After spawning, content of these elements drops to their minimum. In female gonads, in the course of oocyte maturation from the 2nd to the 4th maturity stage, considerable accumulation of fat and protein takes place. Protein content in muscles is normally maintained at a constant level. The dynamics of the studied indicators is shown in Figures 2-8. Results of the investigation of the physiological status of the Azov Sea roach have made it possible to determine a physiological norm for this fish species for the present time. The fat content varies by season from 5.7 to 10.2% in muscles, and from 10.2 to 50.4% in liver. Its decrease during pre-spawning (down to less than 3% in muscles and less than 8 % in liver) affects the normal course of fish maturation and, later on, interferes with successful embryogenesis. The protein content in roach muscles is relatively stable; its optimal values lie within the range 130-170 mg/L. The protein content in muscles that is lower than 100 mg/g is considered critical. Optimal values of the protein content in ripe eggs of roach females range between 150 and 250 mg/g, and for the fat content they are no lower than 7-8%. High content of protein (58-100 g/L), lipids (2.0-3.8 g/L) and cholesterol (5.9-15.9 mmol/L) is recorded in blood serum during fattening; in the pre-spawning season, their amount decreases. Total protein content in the blood serum of roach females being higher than 80 g/L during the pre-spawning season indicates the beginning of resorption processes in reproductive products, which is supported by the data collected during histological surveys. The content of protein lower than 30 g/L, of lipids lower than 0.50 g/L, and cholesterol lower than 2.6 mmol/L is indicative of emaciation in fish, and attests to the unfavorable environment.