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In the present study, quantitative real-time RT-PCR was used to monitor the transcriptional responses of seven key genes related to some innate immune pathways in shrimp postlarvae after being placed in a recirculating aquaculture system (RAS) with or without biofloc (BF or no-BF). Each system consisted of the main tank with 400 L of seawater and six glass aquariums (50 L each). Besides, the nucleotide sequences of myosin light chain (LvMyo) from Litopenaeus vannamei related to the phagocytosis pathway were described. The sequence analysis indicated that LvMyo is a conserved protein among crustaceans and is present in other arthropods. The transcriptional response to the treatments showed several expression patterns. The prophenoloxidase gene was up-regulated in both systems (P < 0.05) and was higher in BF than in no-BF (P < 0.01). Phagocytosis-related genes depicted differential expressions. LvMyo, Ras-associated binding 6, and Ras-related nuclear protein expressions were higher in BF than in no-BF (P < 0.05). Regarding antioxidant genes, glutathione peroxidase was up-regulated only in BF (P < 0.05). Superoxide dismutase expression was lower in BF at 12 h (P < 0.05), but higher at 24 h (P < 0.05). These findings suggest that biofloc modulates the transcription of genes related to the immune response in shrimp as an early response or at the mid-term. Besides, the biological filter in a RAS without biofloc seems to be able to maintain a bacterial population that promotes a lower but similar response to that induced in the biofloc system.

Sportfishing is a growing segment in the fishing sector, which requires the supply of marine shrimps to meet the demand for live baits; however, the extraction of white shrimp from their natural habitat results in overfishing depleting natural stocks. Intensive cultivation in water recirculation system is a worldwide trend for shrimp farming, which, in addition to increasing productivity, minimizes the impact of effluent emission on the environment, reinforcing sustainability. This study analyzed the economic viability of establishing farms for the cultivation of white shrimp (Litopenaeus schmitti) in water recirculation system to meet the market demand of sportfishing for live baits. The indicators were used: internal rate of return (IRR), net present value (NPV) and payback period (PP). The best scenario, with 90 % survival rate and unitary selling prices of US$ 0.50, showed IRR 11.74 %, NPV (10 %) US$ 1,241.88 and PP 5.71 years, demonstrating financial risk for the production of live baits in the conditions proposed in this study.

The growth and biochemical profile of the red seaweed Gracilaria corticata var. cylindrica was evaluated after in vitro cultivation with effluent from a shrimp Litopenaeus vannamei farming pond. Seaweeds were cultivated for 21 days in sterilized seawater enriched with shrimp effluent with 5 different concentrations (0.1, 1, 10, 50, and 100 mL L−1). Fragments with 50 and 100 mL L−1 showed a higher significant growth rate of 3.53 ± 0.08% and 3.7 ± 0.55% respectively compared to sterilized seawater as control (2.5 ± 0.15%). Survival and regeneration of fragments were higher in the treatments 10, 50 and 100 mL L−1. A 100% survival was observed in 10 and 100 mL L−1, while 100-mL L−1 showed 100% regeneration in fragments. The number of branchlets developed per fragment was observed higher (2.33 ± 0.52) and (2.23 ± 0.05) in 50 and 100 mL L−1 respectively. A 50 mL L−1 showed the highest (124.45 ± 9.28 µg g−1) chlorophyll-a, and 100 mL L−1 showed the highest (54.5 ± 5.42 µg g−1) chlorophyll-b content. Agar yield (2.8 ± 0.32% FW), total sugar (72.6 ± 2.7%), and 3,6-anhydrogalactose (8.77 ± 0.63%) was observed highest in 100 mL L−1 treatment of shrimp effluent, while sulphate content (1.5 ± 0.8%) found higher in 50 mL L−1. Results showed that effluent treatments positively affected G. corticata var. cylindrica growth and biochemical composition, especially 50 and 100 mL L−1, which could be considered a good bio-stimulator for the making of the seedling. This work presents the potential use of effluents from shrimp cultivation as fertilizer, improving the growth and seedling production for sustainable cultivation of endemic red seaweed Gracilaria corticata var. cylindrica.

Changes in temperature cause various bodily reactions in fish, such as activating their stress response and producing heat shock proteins (HSPs). These HSPs are important for counteracting stress by supporting antioxidant systems and immune responses. In the present study, our aim was to investigate the efficiency of Tex-OE®, a compound derived from prickly pear fruit (Opuntia ficus-indica), in inducing HSP70 production for the purpose of protecting stellate sturgeon fry from thermal stress. The fry was exposed to Tex-OE® as an HSP inducer (HSPi) at a concentration of 100 mg L−1 for a duration of 4 h. Subsequently, they were subjected to two thermal stresses (22 °C and 26 °C) to assess the potential of Tex-OE®. The expression of HSP70 gene; the immune parameters (lysozyme, IgM, and C3); antioxidant enzymes (including SOD, CAT, and T-AOC); and cortisol levels were measured. The findings revealed that applying HSPi before subjecting fish fry to thermal stress increased HSP70 gene expression. In addition, fish that were pre-treated with Tex-OE® and subsequently exposed to temperature stress exhibited higher levels of antioxidant enzymes and immune parameters as well as a decrease in cortisol compared to fish that were only exposed to temperature stress. In conclusion, our findings highlight the efficacy of Tex-OE® as an HSP inducer capable of promoting HSP70 production in stellate sturgeon fry. The induction of HSP70 by Tex-OE® demonstrated promising stress protection against thermal stress by modulating the expression of HSP70, immune system parameters, antioxidant enzymes, and cortisol levels.

Fish transportation is a regular farming and experimental practice that mainly results in stress conditions that may extend to induce a high mortality rate. In the present experimental simulation, Oreochromis niloticus were transported for 2 h and maintained for another 6 h in transportation containers to assess the effect of tranquilization with tricaine methanesulfonate (MS-222) and/or the addition of iodine on mortality rate and restoring the normal physiological functions. Experimental fish were divided into four groups: group 1 (control) was transported in farm water without MS-222 or iodine, group (2) was transported in farm water supplemented with 40 mg/L of MS-222, fish in group (3) were transported in farm water supplemented with 40 mg/L of MS-222 + 10 ppm iodine, and fish in group (4) were transported in farm water containing 10 ppm iodine. Blood samples were collected for the determination of serum cortisol and glucose, while skin mucus was collected for assaying lysozyme, peroxidase and antibacterial activity; cumulative mortality rate; and food reflexes which were assessed at 0 h, 1 h, 6 h, 48 h, 7 days and 14 days post 2 h transportation. The results indicated that fish tranquilization with MS-222 and/or treatment with iodine mitigated the stress condition associated with transportation and accelerate restoration of the normal physiological and immunological status. So, it was recommended to use the MS-222 as a tranquillizer together with iodine as an antiseptic during transportation of O. niloticus.

Studies were conducted to explore the effect of cohort sampling and stocking density on the interactions between plasma growth hormone (GH), thyroid hormone and cortisol concentrations in rainbow trout. Depending on the experimental design, plasma GH concentrations were either suppressed, or elevated by sequential removal of cohorts from the holding aquarium. Since plasma cortisol concentrations consistently increased during cohort sampling, regardless of experimental design, it would appear that the apparent correlation (direct or inverse) is the result of concomitant changes, i.e. not necessarily a cause-effect relationship. Plasma GH concentrations of rainbow trout were not correlated with eviscerated body weight. Trout stocked at 150 kg m−3 exhibited a significantly lower mean growth rate, hepatosomatic index, hepatic lipid reserve, plasma triiodo-l-thyronine (T3) concentration andin vitro hepatic T3 production than trout stocked at 60 kg m−3. These observations are consistent with the former group being food deprived or ration restricted. Stocking density appeared to have no effect on plasma GH or cortisol concentrations, or on the pituitary-interrenal axis response to stressor challenge, or the thyroid tissue response to exogenous TSH challenge.

Adhesion of sperm to a glass surface can be manifested by the low percentage of motile spermatozoa and lower speed. This crucial factor could disprove the sperm quality prediction from computer-assisted sperm analysis (CASA) results. In our study, this was particularly observed when solution L was used. However, protein supplementation was effective in the reduction in sperm adhesion. We found that albumin increased the sperm motility at concentrations of 0.25 % in solution L and 0.5 % in solution P. Casein was effective in both solutions at 0.25 % concentration. However, in solution L, the motility was lower than that measured in solutions P and L with the supplementation of BSA at 0.25 and 0.5 %. BSA supplementation was especially beneficial in terms of higher speed values regardless of an activation solution. Casein used with solution P allows us to obtain similar results as in the samples activated with BSA supplementation. Casein supplementation to solution L did not increase CASA results to the level observed in the samples activated with BSA added to the solution L. Our data suggest that the selection of an activation solution is one of the most crucial steps in the experiments requiring CASA data. Depending on the composition, different protein supplements should be used to reduce adhesion of sperm to a glass surface. We recommend the use of BSA at the 0.5–1 % concentration because at this level we obtained the highest CASA parameters in both activation media.

A meta-analysis of published results was used to quantify differences in mortality and growth of freshwater fish larvae when live feed was replaced by compound diets at first feeding. A mean relative risk of 2.4560 (95% confidence interval = 2.0879–2.8891), calculated with 75 observations from 47 studies conducted with 27 freshwater fish species according to a random effects model, indicated that larvae fed on compound diets have a 2.5 times higher chance to die than those fed on live feed. Compared to Artemia nauplii as sole live feed, compound diets were more effective (causing a lower mortality) when replacing zooplankton other than Artemia nauplii. A mean effect size (Hedges’ d) of −3.1813 (95% confidence interval = −3.8099 to −2.5527), calculated (random effects model) from 51 values determined in 33 studies with 21 fish species, represents the size of the negative effect that compound diets would have on growth of larvae. Numerical differences obtained in this study could be use to monitor future development of larval diets.

To further enhance our understanding of hypoxia tolerance in the fish Phoxinus lagowskii, hypoxia-inducible-factor (HIF) genes were cloned to analyze their biological function during hypoxia exposure. The complete cDNAs of HIF-1α, HIF-2α, and HIF-3α were 2912, 3444, and 2228 bp in length, encoding 773, 829, and 641 amino acid residues, respectively. The HIF-1α and HIF-2α proteins contain HLH, PAS-A, PAS-B, PAC, N-TAD, and C-TAD domains, while HIF-3α has no C-TAD domain. A high number of serine residues in the oxygen-dependent degradation (ODD) domain are connected with hypoxia tolerance in fish. More than 40 serine residues were found in the ODD domain of HIF-α genes in P. lagowskii, suggesting that P. lagowskii has a high potential for hypoxia tolerance. The HIF-α genes were highly expressed in the heart, spleen, and liver of P. lagowskii, suggesting an important role for these genes in modulating the circulatory and metabolic responses to hypoxia. Relative long-term hypoxia exposure and recovery resulted in significantly increased transcript abundance for three genes in liver, gill, and spleen, but short-term exposure and recovery did not, which is indicative of a unique characteristic of hypoxia-tolerant fish. In addition, this study found for the first time that P. lagowskii upregulates HIF-3α within 24 h of liver hypoxia, confirming that HIF-3α plays an important role in liver homeostasis. Therefore, we performed fluorescence in situ hybridization on HIF-3α after inducing liver hypoxia. We also constructed an overexpression vector pcDNA3.1-HIF-3α and transfected it into CIK cells. The results showed that overexpression of HIF-3α significantly increased the expression of hypoxia-related genes such as P53, Glut1, VEGF, and VHL. Moreover, our results showed that enzymes of the defense and antioxidant mechanisms showed a noticeable increase in relatively long-term hypoxia to counteract the oxidative stress generated after re-oxygenation.