Oogenesis in fishes follows a universal plan; yet, due to differences in the synchrony and rate of egg development, spawning frequency varies from daily to once in a lifetime. Some species spawn and feed in separate areas, during different seasons, by storing energy and drawing on it later for reproduction (i.e. capital breeding). Other species spawn using energy acquired locally, throughout a prolonged spawning season, allocating energy directly to reproduction (i.e. income breeding). Capital breeders tend to ovulate all at once and are more likely to be distributed at boreal latitudes. Income breeding allows small fish to overcome allometric constraints on egg production. Income breeders can recover more quickly when good-feeding conditions are re-established, which is a benefit to adults regarding bet-hedging spawning strategies. Many species exhibit mixed capital- and income-breeding patterns. An individual's position along this capital–income continuum may shift with ontogeny or in relation to environmental conditions, so breeding patterns are a conditional reproductive strategy. Poor-feeding environments can lead to delayed maturation, skipped spawning, fewer spawning events per season or fewer eggs produced per event. In a few cases, variations in feeding environments appear to affect recruitment variability. These flexible processes of energy acquisition and allocation allow females to prioritize their own condition over their propagules' condition at any given spawning opportunity, thereby investing energy cautiously to maximize lifetime reproductive value. These findings have implications for temporal and spatial sampling designs, for measurement and interpretation of fecundity, and for interpreting fishery and ecosystem assessments.

Energy Acquisition and Allocation to Egg Production in Relation to Fish Reproductive Strategies

Insulin-like growth factor 1 (IGF-1) is a key hormone that regulates fish growth. It acts on a variety of organs and regulates multiple signaling pathways. In order to explore the specific effects of IGF-1 on fish nutrient absorption, immune system, and other functions, the present study investigated the transcriptional changes of stomachs in tilapia by IGF injection. The tilapias were divided into two groups which were injected with saline (C group) and IGF-1 (2 μg/g body weight) (I group), respectively. After three times injections, the stomachs from the tested tilapias were collected 7 days post the first injection and the transcriptomes were sequenced by Illumina HiSeqTM 2000 platform. The results showed that a total of 155 DEGs were identified between C and I groups. By gene ontology (GO) enrichment analysis, two GO terms related to absorption function were enriched including organic acid transport, and amino acid transport which contained 6 functional DEGs. The Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis suggested that Staphylococcus aureus infection, as well as complement and coagulation cascades pathways were enriched and contained 6 DEGs. Taken together, the present study indicated that IGF-1 injection altered gene expression related to amino acid transporting, complement and coagulation cascades which provides a promise immunopotentiation therapy by IGF-1 in digestive tract of tilapia.

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Insulin-like growth factor 1 injection changes gene expression related to amino acid transporting, complement and coagulation cascades in the stomach of tilapia revealed by RNA-seq

Ghrelin –a stomach derived peptide- acts, in general, as a negative feedback signal for reproductive functions affecting gonadotropin secretion, oocyte maturation and early embryo development. In a previous study we have shown that ghrelin at 800pg/ml accelerates in vitro maturation of bovine oocytes, reducing embryo yield (Dovolou et al 2014; RDA 49,665-72). Here we studied the role and possible mode of action of ghrelin on in vitro maturation of bovine oocytes. In exp. 1, in 3 replicates, COCs (n = 632) collected from abattoir material were matured in vitro for 18 or 24 hours in the presence of 0 or 800pg/ml of acylated bovine ghrelin (groups G18, G24, C18, C24). Matured oocytes were co-cultured for 24h with thawed bull semen, and presumptive zygotes were cultured for 9 days at 390 C, 5%CO2, and 5% O2 . Cleavage and blastocyst formation rate were assessed on days 2 and 7 to 9, respectively and statistical analysis was carried out by one-way repeated measures ANOVA, with arcsine transformation. Exp. 1 served as internal control for the ensuing study on proteins. In exp. 2, after 0,6,10,18 and 24h in maturation, subsets of maturing COCs (each n = 10 in three replicates, totally n = 270) were mechanically denuded from the surrounding cells and cumulus cells and oocytes were separately stored in liquid N2 for the assessment of activation of Akt and Erk1/2 pathways. Whole-cell extracts were prepared by lysis on ice using a buffer containing Tris-HCl NaCl, EDTA, Triton X-100, sodium deoxycholate containing protease inhibitors cocktail and sodium orthovanadate and assays were performed as recommended by the manufacturer (EMD Millipore, Darmstadt, Germany). Phospho-Akt1/PKBalpha (Ser473) and phospho-Erk/MAP Kinase 1/2 (Thr185/Tyr187) beadmates were used together. Protein expressions were measured on a Luminex 100 instrument (Luminex Corporation). The data output gives the mean fluorescence intensity (mFI) as a measure of protein abundance. We calculated the ratio of phosphoprotein mFI to number of treated or un-treated oocytes and cumulus cells and results were analyzed by ttest. In exp. 1 no difference existed in cleavage rate between groups. G24 yielded significantly less (P < 0.03) day 7 blastocyst in comparison to those of C18, C24 and G18 (16.3% , 29.3%, 26.9% and 30.0%, respectively). In exp. 2, it was found that at 18 and 24 hours ghrelin caused significant increased phosphorylation of Akt in cumulus cells in comparison to the respective controls (pAkt/total Akt : 18h, 1.12 ± 0.1 and 0.79 ± 0.15; 24h, 0.99 ± 0.04 and 0.72 ± 0.08, for ghrelin and control groups). Oocytes matured in the presence of ghrelin at 10 h expressed lower Akt phosphorylation rate compared to controls (0.77 ± 0.13 and 1.21 ± 0.09). At 6 hours Erk1/2 phosphorylation was increased in ghrelin treated oocytes compared to the respective controls (11.48 ± 3.9 vs 6.08 ± 1.6). We infer that ghrelin exerts antiapoptotic and antioxidant actions through the cumulus cells, and accelerates maturation via early phosphorylation of Erk1/2 that possibly brings about early activation of the maturation promoting factor.

Effects of ghrelin on activation of Akt and Erk1/2 pathways during in vitro maturation of bovine oocyte

Ghrelin, glucagon-like peptide-1 (GLP-1), and peptide YY (PYY) are potent hormones mediating food intake according to the nutritional status in fish. However, limited information is available on these genes and their expression in response to nutrition in silver pomfret (Pampus argenteus). A comparison analysis revealed that ghrelin and GLP-1 were relatively conserved in marine fish. PYYa and PYYb shared a low identity and were clustered to different PYY branches. Ghrelin, pyya, and pyyb mRNAs were highly expressed in the brain, while glp-1 was highly expressed in the gills and liver. The ghrelin mRNA expression was relatively high an hour post-feeding and decreased after 3 to 72 h of fasting. The glp-1 mRNA expression was increased after 6 to 24 h of fasting. The pyya mRNA expression was increased after 72 h of fasting, while the pyyb expression remained stable during fasting. The diet with 14% lipid promoted the expressions of glp-1, pyya, and pyyb, but inhibited the ghrelin expression. The ghrelin expression in the intestine was increased after palmitic acid, oleic acid (OA), linoleic acid (LA), α-linolenic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) incubation. OA decreased the expression of glp-1 and increased the expression of pyya. The expression of pyyb was downregulated by LA, DHA, and EPA. These results suggest the importance of ghrelin, glp-1, and pyy in coordinating food intake in response to fasting, dietary lipid concentration, and fatty acids in silver pomfret.

https://www.mdpi.com/2410-3888/8/3/170/pdf?version=1682332675

Molecular Characterization and Expression Response of Ghrelin, GLP-1 and PYY to Fasting, Dietary Lipid, and Fatty Acids in Silver Pomfret (Pampus argenteus)

/pdf/first-insights-about-orexigenic-activity-and-1bxu7blq.pdf

First insights about orexigenic activity and gastrointestinal tissue localization of ghrelin from Corvina drum (Cilus gilberti)

Ghrelin is a multifunctional peptide hormone which dominantly secreted in stomach and intestine. Ghrelin involves in growth control, food intake, energy balance, and reproductive process. Recent evidences suggested that ghrelin also interacts with hypothalamic–pituitary–gonadal axis (HPG axis) and controls gametes maturation. In addition, current clues showed that via regulating ghrelin system (acyl ghrelin: des acyl ghrelin ratio, GOAT, GHS-R1a), glucose and weight could be regulated promising a potential way for artificial controlling of gonadal development and gamete maturation. The ghrelin signaling system may be a new target for reproductive operation in fish artificial propagation and breeding. This review summarizes the recent studies of the function of ghrelin in fish reproduction and the regulatory methods for ghrelin system.

Fan Yu

Papers

A review on ghrelin and fish reproduction