Interactions of long-term food ration variation and short-term fasting on insulin-like growth factor-1 (IGF-1) pathways in copper rockfish (Sebastes caurinus).

Variation in food intake affects somatic growth by altering the expression of hormones in the somatotropic endocrine axis including insulin-like growth factor-1 (IGF-1). Here, we examined IGF-1 pathway responses to long- and short-term variation in food availability in copper rockfish (Sebastes caurinus), a nearshore Pacific rockfish important for commercial and recreational fisheries. Juvenile copper rockfish were raised under differing ration amounts (3% or 9% mass feed·g-1 fish wet mass·day-1) for 140 d to simulate 'long-term' feeding variation, after which some fish from both rations were fasted for 12 d to generate 'short-term' conditions of food deprivation. Rockfish on the 9% ration treatment grew more quickly than those on the 3% ration and were larger in mass, length, and body condition (k) after 152 d. Fish on the 9% ration had higher blood glucose than those on the 3% ration, with fasting decreasing blood glucose in both ration treatments, indicating that both long-term and short-term feed treatments altered energy status. Plasma IGF-1 was higher in rockfish from the 9% ration than those in the 3% ration and was also higher in fed fish than fasted fish. Additionally, plasma IGF-1 related positively to individual variation in specific growth rate (SGR). The positive association between IGF-1 and SGR showed discordance in fish that had experienced different levels of food and growth over the long-term but not short-term, suggesting that long-term nutritional experience can influence the relationship between IGF-1 and growth in this species. Rockfish on the 3% ration showed a lower relative abundance of gene transcripts encoding igf1 in the liver, but higher hepatic mRNAs for IGF binding proteins igfbp1a and igfbp1b. Fasting similarly decreased the abundance of igf1 mRNAs in the liver of fish reared under both the 9% and 3% rations, while concurrently increasing mRNAs encoding the IGF binding proteins igfbp1a, -1b, and -3a. Hepatic mRNAs for igfbp2b, -5a, and -5b were lower with long-term ration variation (3% ration) and fasting. Fish that experienced long-term reduced rations also had higher mRNA levels for igfbp3a, -3b, and IGF receptors isoforms A (igf1rA) and B (igf1rB) in skeletal muscle, but lower mRNA levels for igf1. Fasting increased muscle mRNA abundance for igfbp3a, igf1rA, and igf1rB, and decreased levels for igfbp2a and igf1. These data show that a positive relationship between circulating IGF-1 and individual growth rate is maintained in copper rockfish even when that growth variation relates to differences in food consumption across varying time scales, but that long- and short-term variation in food quantity can shift basal concentrations of circulating IGF-1 in this species.

Complete mitochondrion genome of the endangered Mohave tui chub Siphateles bicolor mohavensis (Cypriniformes: Cyprinidae).

The Mohave tui chub (Siphateles bicolor mohavensis) is an endangered cyprinid fish endemic to the Mojave Desert region of southeastern California, USA. Here, we describe the complete 16,607 base pair (bp) mitochondrial genome of S. b. mohavensis. The mitogenome has a nucleotide base composition of A (29.08%), T (26.91%), G (17.58%), and C (26.43%), and encodes 13 protein subunits, 22 tRNAs, a 12S rRNA of 956 bp and 16S rRNA of 1691 bp, and a 929 bp D-loop control region, each located in the conserved mtDNA structure typical for cyprinid fishes. All protein-coding genes have initiation codons of ATG or GTG, and only the ND1, CO1, ATPase8, NDL4, ND4, ND5, and ND6 genes have complete stop codons. Phylogenetic analyses confirmed the relationship of S. b. mohavensis to several genera of cyprinids (e.g. Gila, Acrocheilus) also endemic to western North America. This characterized mitogenome may help inform management practices for S. b. mohavensis by facilitating future studies on how allopatric populations of this imperiled species are evolving across refuge habitats.