How different rearing temperatures affect growth and stress status of Siberian sturgeon Acipenser baerii larvae

Abstract

Environmental temperature is one of the critical factors affecting fish development. The aim of this study was to examine the impact of three different rearing temperatures (16, 19 and 22°C) throughout the endogenous feeding phase of the Siberian sturgeon Acipenser baerii. This was performed by assessing (a) larval survival and growth; (b) immunofluorescence localization and expression of genes involved in muscle development and growth – myog and Igf1; and (c) stress status through the expression of thermal stress genes – Hsp70, Hsp90α and Hsp90β – and whole body cortisol. Overall survival rate and larval weight did not differ significantly across temperatures. Larvae subjected to 22°C showed faster absorption of the yolk‐sac than larvae subjected to 19 or 16°C. Both at schooling and at the end of the trial, larvae reared at 16°C showed significantly lower levels of cortisol than those reared at 19 or 22°C. IGF‐1 immunopositivity was particularly evident in red muscle at schooling stage in all temperatures. The expression of all Hsps as well as the myog and Igf1 genes was statistically higher in larvae reared at 16°C but limited to the schooling stage. Cortisol levels were higher in larvae at 22°C, probably because of the higher metabolism demand rather than a stress response. The observed apparent incongruity between Hsps gene expression and cortisol levels could be due to the lack of a mature system. Further studies are necessary, especially regarding the exogenous feeding phase, in order to better understand if this species is actually sensitive to thermal stress.

How Different Stocking Densities Affect Growth and Stress Status of Acipenser baerii Early Stage Larvae

“…In lake sturgeon, Reference [50] assessed the impact of the rearing environment during early larval stages and observed an increase in cortisol production from hatching to the beginning of the exogenous feeding in non-stressed larvae and a delay in the HPI axis development in the stressed ones. Moreover, a study performed by our group [17], where the effect of different rearing temperatures was assessed in Siberian sturgeon larvae, suggested that larvae were not able to produce a stress response in terms of cortisol production. The development of the HPI axis is known to occur at different times among species, for instance, before or after hatching, or close to metamorphosis [9,13,14,16,51,52].…”

“…The dry extracts were dissolved in 0.5 mL of PBS and varying aliquots were used for radioimmunoassay (RIA). The entire procedure is detailed in Reference [17].…”

“…Genes involved in cellular stress reactions (glut1, glut2, glut4, and hsp70) and genes involved in growth (igf1 and igf2) and myogenesis (myog) were selected for further molecular analyses. The rpl6 (coding for Ribosomal protein L6) and gapdh (coding for Glyceraldehyde 3-phosphate dehydrogenase) genes were used as reference [17]. Primer sequences for the amplification of hsp70, igf1, myog, rpl6, and gapdh gene fragments, annealing temperatures, and the amplification size of each fragment are described by Aidos et al [17].…”

“…The rpl6 (coding for Ribosomal protein L6) and gapdh (coding for Glyceraldehyde 3-phosphate dehydrogenase) genes were used as reference [17]. Primer sequences for the amplification of hsp70, igf1, myog, rpl6, and gapdh gene fragments, annealing temperatures, and the amplification size of each fragment are described by Aidos et al [17]. Specific primers for the amplification of glut1, glut2, glut4, and igf2 gene fragments were de novo designed.…”

“…The amplification conditions were: 150 nM (final concentration) of forward and reverse primers; 98 • C for 30 s, 40 cycles of 98 • C for 15 s, 58 • C (igf2) or 62 • C (glu1, glut2, glut4) for 30 s; and a melting profile was included after the last amplification cycle. Annealing temperatures were defined according to primers melting temperatures indicated in Aidos et al [17] and in Table 1. Cycle threshold (Ct) values were determined for each gene and normalized using rpl6 and gapdh genes as reference.…”