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

A fungal toxin, aflatoxin B1 (AFB1), undermines growth and stress axes of gilthead seabream (Sparus aurata) with depletion of somatic carbohydrate and lipid reservoirs. The present study assessed the physiological consequences of high stocking density versus low stocking density in seabream juveniles, which had previously been fed with AFB1 supplementation. These stressors are likely to converge by inferring animal welfare and economic profitability in the food animal industry. Interestingly, AFB1 seems to cause physiological and molecular dysfunction in response to overcrowding densities. Our results might be relevant to elucidate a potential risk for fish farming that is often overlooked. 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

Antimicrobial and Toxic Activity of Citronella Essential Oil (Cymbopogon nardus), and Its Effect on the Growth and Metabolism of Gilthead Seabream (Sparus aurata L.)

Aquaculture procedures usually induce stress that affects the physiological status of fish. For this reason, the inclusion of additives in fish feeds to palliate stress might be a good alternative. This study aimed to assess the antimicrobial activity of citronella (Cymbopogon nardus) essential oil (CEO) against bacterial pathogens and to determine its dietary impact on the growth performance of Sparus aurata. In vitro tests confirmed that CEO possesses antimicrobial activity against several fish-specific pathogens. For the in vivo tests, three experimental groups were fed for 60 days with different concentrations of CEO: CTRL (0 mL kg(-1) fish feed); CEO1 (1 mL kg(-1) fish feed); and CEO2 (2 mL kg(-1) fish feed). At the end of the experiment, the physiological status was characterized. Subsequently, the specimens of the CTRL and CEO2 groups were subjected to a challenge with an injection of Poly I:C for immune stimulation. Although S. aurata individuals tolerated CEO inclusion without compromising growth performance, it significantly reduced glycogen in the CEO2 group, concomitant to an increment of total peripheral leucocytes. Moreover, different hematological profiles' responsive patterns against an inflammatory stimulus were observed. In conclusion, our results suggest that the use of CEO as a fish feed additive can prevent bacterial outbreaks and improve potential in vivo disease resistance in S. aurata without negatively affecting growth

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 (similar to 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.This research was funded by Project "Diversificacion de la Acuicultura Espanola mediante la optimizacion del cultivo de Seriola dumerili" JACUMAR 2016 (MAPAMA) and Fondo Europeo Maritimo y de Pesca (FEMP). The authors (A.B. and J.M.M.) belong to the FishWelfare and Stress Network (AGL2016-81808-REDT), supported by the Agencia Estatal de Investigacion (MINECO, Spanish Government)

Low dietary inclusion of nutraceuticals from microalgae improves feed efficiency and modifies intermediary metabolisms in gilthead sea bream (Sparus aurata)

The aim of this work was to evaluate two functional feeds for the gilthead seabream, Sparus aurata, containing low inclusion of two microalgae-based products (LB-GREENboost, LBGb; and LB-GUThealth, LBGh). Fish (12-13 g) were fed for 13 weeks a control diet or one of the four diets supplemented with both products at 0.5% or 1%. LBGb and LBGh did not affect specific growth rate or survival, but increased feed efficiency by decreasing feed intake and enlarging the intestines. LBGb increased hepatosomatic index and reduced cortisol levels in plasma, while both products lowered plasma lactate. Extensive metabolite and metabolic enzyme profiling revealed that microalgae supplementations, especially 1% LBGh: (i) decrease plasma lactate and increase hepatic glycogen, (ii) reduce hepatic gluconeogenesis, (iii) enhance hepatic lipogenic activity and lipid secretion, (iv) led fish to double triglyceride content in muscle and to stimulate its lipid oxidative capacity, and (v) increase the content of monounsaturated fatty acids and the omega-3 alpha-linolenic acid in muscle. This study demonstrates that both microalgae-based products are suited to improve feed efficiency and orchestrate significant changes in the intermediary metabolism in gilthead seabream juveniles

Dietary Use of the Microalga Chlorella fusca Improves Growth, Metabolism, and Digestive Functionality in Thick-Lipped Grey Mullet (Chelon labrosus, Risso 1827) Juveniles

In recent years, a clear emphasis has been placed on replacing fishmeal and fish oil in aquafeeds with other alternative ingredients, including algae, particularly in low trophic omnivorous fish species. This work aimed at evaluating the effects of moderate dietary supplementation with the green microalga Chlorella fusca on growth, metabolism, and digestive functionality in juvenile thick-lipped grey mullet (Chelon labrosus). Fish were fed a control diet (CT) or a diet containing 15% C. fusca (C-15) biomass during 90 days. C. labrosus fed with the C-15 diet showed higher growth performance (in terms of final weight and length, weight gain, and specific growth rate) than the control group. Somatic indices and muscle proximate composition were similar at the end of the feeding trial. Regarding fatty acids profile, C. fusca-fed fish showed a selective retention of docosahexaenoic acid (DHA) in the liver, and arachidonic acid (ARA), eicosapentaenoic acid (EPA), and DHA in the muscle. Dietary inclusion of this microalga significantly increased intestinal total alkaline protease, leucine aminopeptidase, and alkaline phosphatase activities in specimens fed with C-15 diet. Furthermore, intestine histological analysis revealed the absence of damage signs on gut morphology in fish fed the microalgae supplemented diet. Thick-lipped grey mullets fed the C-15 diet increased plasma glucose and decreased plasma lactate. Overall, the effects observed on liver (lipid metabolism, glycolysis and glycogenolysis) enzyme activities, together with adequate fatty acid profile, metabolic response, and gut morphology, and a significant increase in the intestinal mucosa's digestive and absorptive capacity, could explain the positive effects on growth performance obtained in fish fed the microalgae-supplemented diet. In conclusion, the results obtained showed that C. fusca is suitable as dietary ingredient for feeding thick-lipped grey mullet juveniles

Seahorse farming in the Bay of Cádiz

La pesca anual de caballitos de mar en el mundo es de entre 40 y 60 millones de toneladas, lo que supone una sobreexplotación de estas especies. En la actualidad se ha logrado la cría en cautividad de la especie Hippocampus guttulatus; sin embargo, aún no existe una metodología clara de producción, tanto para la reproducción como para el engorde. Este Proyecto propicia el uso de recursos propios presentes en la Bahía de Cádiz, así como desarrollar una actividad acuícola basada en esta especie. Además, este Proyecto podría enmarcarse dentro de la línea de conservación de especies, puesto que es necesario desarrollar sistemas de cría y producción en masa para evitar una pérdida genética relevante en el medio natural, y cubrir a ser posible la demanda del mercado.The annual extractions of sea horses in the world are estimated between 40 and 60 million tons and suppose overexploitation of these species. Actually the reproduction in captivity of the species Hippocampus guttulatus has been got; however, there is not yet a methodology for reproduction and growth of this species in aquaculture. This Project will let the use of the natural resources of Cadiz Bay as well as the development of an aquaculture activity focussed on this species. In addition, this Project could frame in the line of conservation of the species, because it will be necessary to improve technology for the culture of this species to prevent an irreversible genetic loss in the natural habitats, and to satisfyy the demand of the world market.33 página

Two different corticosteroids, cortisol and dexamethasone, modulate the osmoregularory response after hypersaline transfer in the gilthead seabream (Sparus aurata)

Trabajo presentado en el XIII Congreso de la Asociación Ibérica de Endocrinología Comparada, celebrado los días 16 y 17 de septiembre de 2021Corticosteroids control inter alia, metabolism, immunology, osmoregulation, and stress responses. In the present work, we examined the different physiological and molecular responses evoked in the gilthead seabream acclimated to seawater (SW, 38 ppt) after chronic oral administration for 30 days of cortisol (F; 400 mg/kg fish feed) and the synthetic glucocorticoid dexamethasone (DEX; 300 mg/kg fish feed), prior- and post-hypersaline seawater (HSW, 60 ppt) direct transfer for 3 days. After the feeding trial, plasma cortisol levels showed the following pattern: CT > F > DEX. HSW transfer significantly enhanced plasma cortisol levels in the CT group, whereas F and DEX groups showed about half of these values. Na+/K+-ATPase (NKA) activity increased dramatically in the DEX group prior to HSW transfer. Surprisingly gill NKA activity levels in this tissue were recovered to the initial lowest levels for all the groups. Plasma and intestinal fluid osmolalities enhanced significantly after HSW transfer in the DEX group. Intestinal short circuit-current (Isc) showed a more anion absorptive capacity in the posterior intestine (PI) than the anterior. Moreover, F treatment significantly increased this anion absorptive capacity in the PI after HSW transference. Surprisingly HSW significantly decreased the anion absorptive capacity in all intestinal regions, specifically in the PI, indicating the appearance and/ or switch to secretory mechanisms in the intestine to counteract hypersalinity. Furthermore, molecular hypophyseal markers such as the pomcb and the gh were significantly altered/modulated by both pharmacological treatments and HSW challenge.This work was funded by Agencia Estatal de Investigación (Ministerio de Ciencia e Investigación, Spanish Government) (PID2020-117557RB-C22). A. Barany was supported by the University of Cadiz Ph.D. scholarship (UCA/REC01VI/2017)