Growth Patterns in the Saffron Cod, Eleginus gracilis Tilesius (Gadidae), during the First Year of Life

Abstract

Patterns of linear and weight growth during the first year of life in saffron cod from different parts of the range are considered based on measurement data and summarized materials for the species available in literature. The growth within a year is simulated by a logistic function. Individuals from the southern areas of the range have been found to grow significantly faster. The most intense linear growth is observed in the first 4 months of life when body length in larvae and juveniles increases by about 50–60% per month. Then, the relative increment decreases significantly in autumn and winter to a rate no greater than 1–4% by the end of the first year of life. The absolute length increments increase during the first half of the year, reaching a maximum of 25–30 mm per month in late summer and early autumn. In the rest of the year, the absolute increments decrease to 2–3 mm. The weight growth pattern is markedly different from the linear one. The weight growth is most intense and significantly exceeds the linear growth within the first 5 months of life. In this period, the body weight at least doubles each month. The rate of relative increments gradually decreases from the first to the fifth month of life. Afterwards, upon reaching a weight of approximately 5 g, the rate of relative weight increments decreases abruptly, although the absolute increments increase substantially. The maximum weight increments (5–6 g) occur in the sixth–eighth months of life, when fish reach a body length greater than 86 mm. In this short period, the saffron cod gain slightly more than 60% of their first-year weight. The peaks of linear and weight increments are discordant in time, with the lag between them being about 2 months. The maximum body length increments are observed in July–September; the maximum weight increments occurred in September–November.