Temperature affects growth allometry and development patterns in brown trout (Salmo trutta) fry: a multitrait approach

To study the influence of temperature (4, 6, and 12 °C) on the development of brown trout (Salmo trutta) from hatching to the end of metamorphosis, an analysis of allometric growth patterns was conducted to identify two different groups of individuals, namely developmental phases at total lengths (TL) ranging from 2.72 cm at 4 °C to 2.22 cm at 12 °C. Then, a multitrait approach considering different variables like the survival rate, development time, morphometric characteristics, energetic value, and skeletal mineralization was conducted on these two groups. Results indicated that the first growth phase was slower at 4 °C, whereas the second was also slower at this temperature, even though swimming behavior was already present. However, at 12 °C, fry showed a delay in their development (i.e., lower levels of skeletal mineralization and energetic content) during the first growth phase, but they compensated during the second growth phase, reaching the same size in TL when compared with the other temperatures (4 and 6 °C); fry at 12 C° showed low energy reserves. Our study demonstrated that the use of an allometric analysis to identify different developmental stages coupled with a multitrait approach was more efficient than a classical distinction between biological stages (hatching, emergence, first food intake, and exogenous feeding), and this procedure is of interest when evaluating the impact of rearing conditions on early development in fish.