IMPROVING GREAT LAKES AQUACULTURE PRODUCTION
Location: Dairy Forage and Aquaculture Research
Title: Developmental expression and estrogen responses of endocrine genes in juvenile yellow perch (Perca flavescens)
Submitted to: General and Comparative Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 3, 2011
Publication Date: April 1, 2011
Citation: Lynn, S.G., Wallat, G.K., Malison, J.A., Shepherd, B.S. 2011. Developmental expression and estrogen responses of endocrine genes in juvenile yellow perch (Perca flavescens). General and Comparative Endocrinology. 171:151-159.
Interpretive Summary: Yellow perch fillets are a high-value product. In the Great Lakes regions, consumer demand continues to increase despite reduced landings by commercial fisheries. Availability shortfalls have been offset by increasing imports of lesser quality products. For domestic perch production to be competitive with foreign imports, production efficiency will have to be improved. A critical bottleneck in perch production is in the production of viable offspring with high survival and improved growth. In other fish species, it has been shown that the pituitary hormones [growth hormone (GH), prolactin (PRL), and somatolactin (SL)], their intermediary insulin-like growth factor-I (IGF-I, produced in the liver), and the sex steroid estrogen are important hormones that control growth, development, and reproduction. However, nothing is known regarding the involvement of these hormones in the development of yellow perch or how they are related to the occurrence of sexual size dimorphism (SSD: females grow faster than males) in this species. To better understand the biochemical connections between development and SSD, we examined levels of gene expression for GH, PRL, SL, IGF-I, and the two estrogen receptors (alpha and beta) in developing yellow perch that were spawned and reared under typical aquaculture conditions. Our findings demonstrated a linkage between growth and reproductive development in this species which involves an intricate relationship between estrogen and other growth-regulating hormones. Development of these molecular tools will enable us to understand their involvement in commercially important physiological traits.
The present study examines the expression of growth-regulating genes (gh, prl, smtl and igf1b), the estrogen receptors (esr1 and esr2a) and aromatase (cyp19a1a) in developing yellow perch. To gain an initial understanding into the endocrine control of growth preceding and involved with sexual size dimorphism (SSD), where females have been reported to grow faster and larger than males, young-of-the-year fish were sampled for length, weight, and tissues at several time points (102-421 days post-hatch [dph]). Positive growth was seen in both sexes over the sampling interval, but SSD was not manifested. Using real-time quantitative PCR, we found that pituitary growth hormone (gh) and liver insulin-like growth factor-1b (igf1b) mRNA levels were significantly affected by dph, and levels were found to be correlated with growth in both sexes. Liver cyp19a1a, esr1, and esr2a mRNA levels were significantly influenced by dph, whereas there was a significant dph*sex interaction on liver esr2a mRNA levels with males having higher levels than females at 379 and 421 dph. Ovarian cyp19a1a decreased with dph, but there were no changes in esr1 or esr2a mRNA levels. Dietary treatment of juvenile (~300 dph) females with 20 mg/kg diet 17ß-estradiol resulted in significantly higher liver esr1 mRNA levels and a sustained hepatosomatic index (IH). Across all data sets, liver esr2a mRNA levels showed the most significant positive correlation with liver igf1b mRNA levels. These findings show that growth is accompanied by increases in pituitary gh, liver igf1b, and liver esr1 and esr2a mRNAs in juvenile yellow perch.