Abstract
The clown anemonefish (Amphiprion ocellaris) is a common model species in studies assessing the impact of climate changes on tropical coral fish physiology, metabolism, growth, and stress. However, the basic endocrine principles for the control of food intake and energy homeostasis, under normal and elevated sea temperatures, in this species remain unknown. In this work, we studied food intake and growth in clown anemonefish reared at different temperatures and with different food availability. We also analyzed expression of genes in the melanocortin system, which is believed to be involved in the control of appetite and feeding behavior. These were two paralogues of pomc: pomca and pomcb; two paralogs of agrp: agrp1 and agrp2; and one mc4r-like. Groups of juvenile clown anemonefish were exposed to four experimental treatments combining (orthogonal design) two rearing temperatures: 28 °C (T28; normal) and 32 °C (T32; high) and two feeding regimes: one (1 M; 08:00) or three (3 M; 08:00, 12:00, 15:00) meals per day, fed to satiety by hand. The results showed that high temperature (T32) did not affect the average growth rate but induced a stronger asymmetrical individual body weight of the fish within the population (tank). Lower feeding frequency (1 M) resulted in lower growth rates at both rearing temperatures. Fish reared at high temperature had higher total daily food intake, which correlated with a lower expression of pomca, supporting an anorexigenic role of this gene. High temperature combined with restricted feeding induced higher agrp1 levels and resulted in a higher food intake in the morning meal compared to the control. This supports an orexigenic role for agrp1. mRNA levels of agrp2 responded differently from agrp1, supporting different roles for the paralogues. Levels of mc4r-like inversely correlated with fish body weight, indicating a possible size/stage dependence of gene expression. In conclusion, our results indicate that the melanocortin system is involved in adjusting appetite and food intake of clown anemonefish in response to elevated temperature and low food availability.
Highlights
The control of appetite and food intake is essential for maintaining metabolism and supporting growth
One of these regulatory pathways (1) is mediated by α-melanocytestimulating hormone (α-MSH), a potent anorexigenic peptide derived from pro-opiomelanocortin POMC, which acts on target cells in the paraventricular nucleus via the melanocortin 4 receptor (MC4R) (CerdaReverter et al, 2011; Volkoff, 2016; Volkoff et al, 2005)
Fish exposed to the higher temper ature (T32) showed a 20% higher food consumption than the temperatures: 28 ◦C (T28) fish, without contributing to higher growth
Summary
The control of appetite and food intake is essential for maintaining metabolism and supporting growth In fish, this control is mediated through the hypothalamus, which perceives and integrates a set of central and peripheral signals (Delgado et al, 2017; Rønnestad et al, 2017; Soengas et al, 2018). The central control of appetite and food intake is modulated by two opposing signaling loops: (1) anorexi genic – inhibiting and (2) orexigenic stimulation (Volkoff et al, 2005). One of these regulatory pathways (1) is mediated by α-melanocytestimulating hormone (α-MSH), a potent anorexigenic peptide derived from pro-opiomelanocortin POMC, which acts on target cells in the paraventricular nucleus via the melanocortin 4 receptor (MC4R) (CerdaReverter et al, 2011; Volkoff, 2016; Volkoff et al, 2005).
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