Otolith micro-structure analysis of rainbow trout alevins (Oncorhynchus mykiss) under rearing conditions

Otolith microstructure (MO) analysis was used to back-calculate growth patterns from hatching to the yolk-sac absorption in Rainbow trout alevins (Oncorhynchus mykiss), under experimental conditions, from winter to spring in Central-Chile. MO showed the following main features: (i) occurrences of multiple primordia in the central region of otolith (MP); (ii) several increments (22 ± 3 rings) before a prominent hatch check surrounding MP and (iii) existence of a very distinctive check associated to yolk-sac absorption. Further findings were the validation of daily periodicity of micro-increments and a significant linear relationship (P < 0.001; r²= 0.91) between the maximum otolith length (MOL) and total length (TL) of alevins. The linear MOL-TL relationship validated the use of the biological intercept method to back-calculate daily growth rates. Growth rates profiles followed a decreasing trend from hatching to the end of yolk-sac period (16 ± 1 days), ranging from 0.34 mm d^-1 to 0.22 mm d^-1 (0.30 ± 0.037). MO analysis demonstrated to be a powerful tool in back-calculating growth patterns of alevins once they had absorbed their yolk-sac.