Protium heptaphyllum essential oil from the fruit as a sedative and anesthetic in Rhamdia quelen: influence in cardiac frequency, biochemical, and oxidative parameters.

This study aimed to evaluate the effects of Protium heptaphyllum fruit essential oil (PHEO) on the physiology of silver catfish (Rhamdia quelen) during anesthesia and recovery, through studying echocardiograms, oxidative status, and metabolic parameters. Three experiments were performed: (1) 50 silver catfish juveniles were submitted to anesthesia and recovery tests with 300, 400, 500, 600, and 700 mg L-1 of PHEO. (2) Echocardiogram analysis was performed in anesthetized and non-anesthetized fish. (3) Biochemical parameters were evaluated at 0, 30, 60, and 120 min of recovery after being anesthetized for 3 min with 600 mg L-1 PHEO. Times to sedation and deep anesthesia were reduced with PHEO increasing concentrations. The echocardiogram showed a higher cardiac rate in anesthetized fish. Plasma glucose levels increased in control fish through recovery time, but anesthetized fish showed lower levels than controls at 120 min of recovery. Metabolic parameters such as plasma and hepatic glucose did not show changes considering the recovery time of up to 120 min. Hepatic glycogen, lactate, and triglycerides reduced their levels over recovery times. Fish anesthetized enhanced superoxide dismutase activity and thiobarbituric acid reactive substances levels but decreased reduced glutathione (GSH) levels at 30 min compared to controls. After 60 min, GSH values were significantly higher in anesthetized fish than in controls. These results suggest that PHEO at 600 mg L-1 is an effective anesthetic for the rapid handling of silver catfish, providing stable metabolic parameters and enhanced antioxidant responses during recovery. Echocardiogram analysis confirms the anesthetic effect, supporting PHEO as a viable and efficient option for fish anesthesia in aquaculture. The use of PHEO in aquaculture can enhance fish welfare by reducing stress during handling and transportation, potentially leading to improved growth, health, and survival rates.

Osmoregulatory Plasticity of Juvenile Greater Amberjack (Seriola dumerili) to Environmental Salinity.

Osmotic costs in teleosts are highly variable, reaching up to 50% of energy expenditure in some. In several species, environmental salinities close to the isosmotic point (~15 psu) minimize energy demand for osmoregulation while enhancing growth. The present study aimed to characterize the physiological status related to osmoregulation in early juveniles of the greater amberjack, Seriola dumerili, acclimated to three salinities (15, 22, and 36 psu). Our results indicate that plasma metabolic substrates were enhanced at the lower salinities, whereas hepatic carbohydrate and energetic lipid substrates decreased. Moreover, osmoregulatory parameters, such as osmolality, muscle water content, gill and intestine Na+-K+-ATPase activities, suggested a great osmoregulatory capacity in this species. Remarkably, electrophysiological parameters, such as short-circuit current (Isc) and transepithelial electric resistance (TER), were enhanced significantly at the posterior intestine. Concomitantly, Isc and TER anterior-to-posterior intestine differences were intensified with increasing environmental salinity. Furthermore, the expression of several adeno-hypophyseal genes was assessed. Expression of prl showed an inverse linear relationship with increasing environmental salinity, while gh mRNA enhanced significantly in the 22 psu-acclimated groups. Overall, these results could explain the better growth observed in S. dumerili juveniles kept at salinities close to isosmotic rather than in seawater.

Aflatoxicosis Dysregulates the Physiological Responses to Crowding Densities in the Marine Teleost Gilthead Seabream (Sparus aurata).

Several studies in fish have shown that aflatoxin B1 (AFB1) causes a disparity of species-dependent physiological disorders without compromising survival. We studied the effect of dietary administration of AFB1 (2 mg AFB1 kg-1 diet) in gilthead seabream (Sparus aurata) juveniles in combination with a challenge by stocking density (4 vs. 40 g L-1). The experimental period duration was ten days, and the diet with AFB1 was administered to the fish for 85 days prior to the stocking density challenge. Our results indicated an alteration in the carbohydrate and lipid metabolites mobilization in the AFB1 fed group, which was intensified at high stocking density (HSD). The CT group at HSD increased plasma cortisol levels, as expected, whereas the AFB1-HSD group did not. The star mRNA expression, an enzyme involved in cortisol synthesis in the head kidney, presented a ninefold increase in the AFB1 group at low stocking density (LSD) compared to the CT-LSD group. Adenohypophyseal gh mRNA expression increased in the AFB1-HSD but not in the CT-HSD group. Overall, these results confirmed that chronic AFB1 dietary exposure alters the adequate endocrinological physiological cascade response in S. aurata, compromising the expected stress response to an additional stressor, such as overcrowding.

Corticosteroid control of Na+/K+-ATPase in the intestine of the sea lamprey (Petromyzon marinus).

Anadromous sea lamprey (Petromyzon marinus) larvae undergo a months-long true metamorphosis during which they develop seawater (SW) tolerance prior to downstream migration and SW entry. We have previously shown that intestinal Na+/K+-ATPase (NKA) activity increases during metamorphosis and is critical to the osmoregulatory function of the intestine in SW. The present study investigated the role of 11-deoxycortisol (S) in controlling NKA in the anterior (AI) and posterior (PI) intestine during sea lamprey metamorphosis. In a tissue profile, nka mRNA and protein were most abundant in the gill, kidney, and AI. During metamorphosis, AI nka mRNA increased 10-fold, whereas PI nka mRNA did not change. Specific corticosteroid receptors were found in the AI, which had a higher binding affinity for S compared to 11-deoxycorticosterone (DOC). In vivo administration of S in mid-metamorphic lamprey upregulated NKA activity 3-fold in the AI and PI, whereas administration of DOC did not affect intestinal NKA activity. During a 24 h SW challenge test, dehydration of white muscle moisture was rescued by prior treatment with S, which was associated with increased intestinal nka mRNA and NKA activity. These results indicate that intestinal osmoregulation in sea lamprey is a target for control by S during metamorphosis and the development of SW tolerance.

11-Deoxycortisol controls hydromineral balance in the most basal osmoregulating vertebrate, sea lamprey (Petromyzon marinus).

It is unknown whether and how osmoregulation is controlled by corticosteroid signaling in the phylogenetically basal vertebrate group Agnatha, including lampreys and hagfishes. It is known that a truncated steroid biosynthetic pathway in lampreys produces two predominant circulating corticosteroids, 11-deoxycortisol (S) and 11-deoxycorticosterone (DOC). Furthermore, lampreys express only a single, ancestral corticosteroid receptor (CR). Whether S and/or DOC interact with the CR to control osmoregulation in lampreys is still unknown. We examined the role of the endogenous corticosteroids in vivo and ex vivo in sea lamprey (Petromyzon marinus) during the critical metamorphic period during which sea lamprey increase osmoregulatory capacity and acquire seawater (SW) tolerance. We demonstrate in vivo that increases in circulating [S] and gill CR abundance are associated with increases in osmoregulatory capacity during metamorphosis. We further show that in vivo and ex vivo treatment with S increases activity and expression of gill active ion transporters and improves SW tolerance, and that only S (and not DOC) has regulatory control over active ion transport in the gills. Lastly, we show that the lamprey CR expresses an ancestral, spironolactone-as-agonist structural motif and that spironolactone treatment in vivo increases osmoregulatory capacity. Together, these results demonstrate that S is an osmoregulatory hormone in lamprey and that receptor-mediated discriminative corticosteroid regulation of hydromineral balance is an evolutionarily basal trait among vertebrates.