Cloning and characterization of <Emphasis Type="Italic">Bax1</Emphasis> and <Emphasis Type="Italic">Bax2</Emphasis> genes of <Emphasis Type="Italic">Ctenopharyngodon idellus</Emphasis> and evaluation of transcript expression in response to grass carp reovirus infection

Multidomain proapoptotic Bcl-2-associated X (Bax) protein is an essential effector responsible for mitochondrial outer membrane permeabilization, resulting in cell death via apoptosis. In this study, two Bax genes of grass carp (Ctenopharyngodon idellus), designated as CiBax1 and CiBax2, were isolated and analyzed. The obtained CiBax1 cDNA is 2058 bp long, with a 579 bp open reading frame (ORF) coding a protein of 192 amino acid residues. The full-length cDNA of CiBax2 is 1161 bp, with a 618 bp ORF coding 205 amino acids. Both CiBax1 and CiBax2 are typical members of Bcl-2 family containing conserved Bcl and C-terminal domains, and they share conserved synteny with zebrafish Bax genes despite the grass carp Bax mapping to different linkage groups. Phylogenetic analysis showed that CiBax1 was clustered with Bax from most teleost fish, and CiBax2 was close to Bax2 from teleost fish but far separated from that of Salmo salar. Quantitative real-time PCR analysis revealed broad expression of CiBax1 and CiBax2 in tissues from healthy grass carp, but the relative expression level differed. The mRNA expression of CiBax1 and CiBax2 was both upregulated significantly and peaked in all examined tissues at days 5 or 6 post-infection with grass carp reovirus. Subcellular localization indicated that CiBax1 protein was localized in both nucleus and cytosol, while CiBax2 protein only in cytosol. Moreover, CiBax2, but not CiBax1 was colocalized with mitochondrion under normal condition. Taken together, the findings would be helpful for further understanding of the function of Bax in teleost fish.     

Development of a simple and rapid monoclonal antibody-based flow through immunogold assay (FIA) for detection of <Emphasis Type="Italic">Aeromonas hydrophila</Emphasis>

In this study, we developed a simple, low-cost, and rapid flow through immunogold assay (FIA) for detection of Aeromonas hydrophila in fish tissues and validated. The developed assay relied on colloidal gold conjugated highly specific monoclonal antibody (B8E3) against 20 kDa protein of A. hydrophila. The assay can be completed within 5 min including antigen (sample) preparation and exhibited no cross-reaction with other major aquatic pathogens such as Vibrio anguillarum, V. parahaemolyticus, V. harveyi, white spot syndrome virus (WSSV), and Aphanomyces invadans. A wider range of Aeromonas species were tested including A. caviae, A. dhakensis, A. sobria, A. veronii, A. culicicola, A. sharmana, and A. schubertii and no cross-reactivity could be observed. The developed technique FIA could detect 10³ CFU/ml of aeromonad cells. In addition, the FIA is as sensitive as the first-step polymerase chain reaction (PCR) and 1000 times sensitive than the immunodot blot method. The validation study revealed the accuracy of FIA by comparing with the standard first-step PCR. The proposed FIA is low-cost, easy-to-use, and compatible for field-level analysis of A. hydrophila in fish tissues. Our developed FIA could successfully detect A. hydrophila at early stage of the infection and could be easily availed by farmers, fish producers, non-technicians, and technicians in the aquaculture industry.     

The effects of starvation on fast-start escape and constant acceleration swimming performance in rose bitterling (<Emphasis Type="Italic">Rhodeus ocellatus</Emphasis>) at two acclimation temperatures

To investigate the effects of starvation and acclimation temperature on the escape ability of juvenile rose bitterling (Rhodeus ocellatus), we measured the fast-start escape and constant acceleration swimming performance of fish fasted for 0 (control), 1 and 2 weeks and half-lethal periods (6 or 4 weeks) at two temperatures (15 and 25 °C). Fish acclimated at a high temperature exhibited shorter response latency (R), higher maximum linear velocity (V _max) and longer escape distance during escape movement (D _120ms) than those at the low temperature. Starvation resulted in a significant decrease in V _max and D _120ms at either low or high temperature and a significant increase in R at only the high temperature in the half-lethal period groups (P < 0.05). The relationship between V _max (Y, m s^?1) and starvation time (X, week) was Y ₁₅ = ?0.062X + 1.568 (r = ?0.665, n = 36, P < 0.001) at low temperature and Y ₂₅ = ?0.091X + 1.755 (r = ?0.391, n = 40, P = 0.013) at high temperature. The relationship between U _cat (Y, cm s^?1) and starvation time (X, week) was Y ₁₅ = ?1.649X + 55.418 (r = ?0.398, n = 34, P = 0.020) at low temperature and Y ₂₅ = ?4.917X + 62.916 (r = ?0.793, n = 33, P < 0.001) at high temperature. The slopes of equations showed a significant difference between low and high temperature (F _1,63 = 9.688, P = 0.003), which may be due to the different energy substrate utilization when faced with food deprivation at different temperatures.     

Monitoring of <Emphasis Type="Italic">Francisella noatunensis</Emphasis> subsp. <Emphasis Type="Italic">orientalis</Emphasis> in farmed Nile tilapia (<Emphasis Type="Italic">Oreochromis niloticus</Emphasis>) in Brazil

Francisella noatunensis orientalis is a bacterium that causes emerging bacteriosis in Nile tilapia (Oreochromis niloticus) in many parts of the world, including Brazil. It is a non-motile, Gram-negative, strictly aerobic, facultative intracellular coccobacillus. This species of bacteria is responsible for low to high mortality in fish farms, causing economic losses for fish farmers. This study aimed to detect the presence of F. noatunensis orientalis using qPCR (real-time polymerase chain reaction) and to describe lesions caused by the bacterium in O. niloticus in Brazilian aquaculture. For this purpose, 360 fish from six fish farms (30 per farm) were sampled at two time points (n = 180 per sampling). Necropsies and histopathology were performed for lesion observation, in addition to qPCR and sequencing for detection and identification of Francisella species. Environmental data were collected using a multiparameter sonde YSI EXO2. All measured limnological variables were within the optimum range for cultivation of Nile tilapia. The major lesions present were melanization of the skin, splenomegaly, granulomas, and inflammatory cell responses. The prevalence of francisellosis varied from 0 to 86.66% between time periods and fish farms analyzed, and an outbreak was observed during the second sampling period. This study describes the prevalence of francisellosis in O. niloticus and reports that the lesions found are not exclusively associated with this bacterial disease.     

Toxicological and hematological effect of <Emphasis Type="Italic">Terminalia arjuna</Emphasis> bark extract on a freshwater catfish, <Emphasis Type="Italic">Heteropneustes fossilis</Emphasis>

Increasing demand for eco-friendly botanical piscicides and pesticides as replacements for harmful synthetic chemicals has led to investigation of new sources of plant materials. Stem bark of Terminalia arjuna, which has been used as a popular folk medicine since ancient time, was examined for its piscicidal activity. This study aims to determine toxicity of ethanol extract of T. arjuna bark on fresh water stinging catfish (Heteropneustes fossilis), along with evaluation of changes in hematological parameters of the fishes exposed to a lethal concentration. The percent mortality of fishes varied significantly in response to concentrations of the extract and exposure times (between exposure time F = 36.57, p < 0.001; between concentrations F = 39.93, p < 0.001). The lethal concentrations (LC₅₀) of ethanol extract were found to be 12.7, 8.94, 5.63 and 4.71 mg/l for 24, 48, 72 and 96 h, respectively. During acute toxicity test, blood samples of treatment fishes showed significant decreases in the red blood cells count, hematocrit content, hemoglobin concentration, mean corpuscular hemoglobin concentration and plasma protein level when compared to those of the control group, while there were significant increases in the mean corpuscular volume, mean corpuscular hemoglobin, white blood cells count and plasma glucose concentration. These results suggest that T. arjuna bark extract could be considered as a potent piscicide due to its toxic effect on fish, particularly fish hematology.     

Alternative microalgal diets for cultivation of the fairy shrimp <Emphasis Type="Italic">Branchinella thailandensis</Emphasis> (Branchiopoda: Anostraca)

Fairy shrimp is known as a nutritional food for fish and crustaceans in aquaculture. In most hatcheries, the microalga Chlorella sp. appears to be the most common, suitable, and nutritious food to feed fairy shrimp. In this study, we attempted to determine other alternative algal diets for cultivation of fairy shrimp Branchinella thailandensis. Seven experimental diets including three treatments of dried Spirulina sp. at 0.75 (S1), 1.5 (S2), and 3.0 mg dry weight individual^?1 (S3); three treatments of Chlorococcum humicola at 5 × 10⁵ (Ch1), 1 × 10⁶ (Ch2), and 2 × 10⁶ cells mL^?1 (Ch3); and a control diet (Chlorella vulgaris at 1 × 10⁶ cells mL^?1) were fed to 5-day-old shrimp for 15 days. Evaluation of growth performance, egg production, survival percentage, and nutritional and carotenoid content of the experimental fairy shrimp revealed that Ch3 is the most suitable algal diet. Our results suggest that C. humicola is the best alternative food source for the cultivation of B. thailandensis. In addition, dried Spirulina powder is also a good choice when live algae are not available and can be used as an alternative feed in fairy shrimp cultures.     

Pre-sedation and transport of <Emphasis Type="Italic">Rhamdia quelen</Emphasis> in water containing essential oil of <Emphasis Type="Italic">Lippia alba</Emphasis>: metabolic and physiological responses

The effects of transporting silver catfish (Rhamdia quelen) for 6 h in plastic bags containing 0 (control), 30 or 40 µL/L of essential oil (EO) from Lippia alba leaves were investigated. Prior to transport, the fish in the two experimental groups were sedated with 200 µL/L of EO for 3 min. After transport, dissolved oxygen, carbon dioxide, alkalinity, water hardness, pH, temperature and un-ionized ammonia levels in the transport water did not differ significantly among the groups. However, total ammonia nitrogen levels and net Na⁺, Cl^? and K⁺ effluxes were significantly lower in the groups transported with EO of L. alba than those in the control group. PvO₂, PvCO₂ and HCO₃ ^? were higher after transporting fish in 40 µL/L of EO of L. alba, but there were no significant differences between groups regarding blood pH or hematocrit. Cortisol levels were significantly higher in fish transported in 30 µL/L of EO of L. alba compared to those of the control group. The metabolic parameters (glycogen, lactate, total amino acid, total ammonia and total protein) showed different responses after adding EO to the transport water. In conclusion, while the EO of L. alba is recommended for fish transport in the conditions tested in the present study because it was effective in reducing waterborne total ammonia levels and net ion loss, the higher hepatic oxidative stress in this species with the same EO concentrations reported by a previous study led us to conclude that the 10–20 µL/L concentration range of EO and lack of pre-sedation before transport are more effective.     

A convenient and nondestructive method using bio-impedance analysis to determine fish freshness during ice storage

Fish freshness can be assessed through K values, but this method has a number of limitations, including a complex procedure and destructive sampling. With the aim to develop a convenient method of assessing fish freshness, we measured the changes in K values (up to 40%) and bio-impedance (Z value; frequency 2, 5, 20, 50, 100 kHz) of ordinary muscle in fish of eight marine species, all caught in the East China Sea, during ice storage and examined their relationships. The results indicated that the K value in all fishes increased linearly with storage time, while their Z value decreased only after 24 h of storage. Moreover, after 24 h of storage and at K values of < 40%, impedance ratios at 2–100 kHz (C value, C?=?Z_{2 kHz}/Z_{100 kHz}) were significantly correlated (p ?<?0.05) with both storage time and K values in all fishes. These findings suggest that the bio-impedance ratio effectively reflects the change in ATP-related compounds of fish and that a convenient, nondestructive method using the C value can be used instead of the complicated K value measurement to assess the freshness of marine fishes after 24 h of ice storage.     

Cloning,characterization, and molecular expression of gonadotropin receptors in European hake (<Emphasis Type="Italic">Merluccius merluccius</Emphasis>), a multiple-spawning species

Teleosts have many spawning strategies and the hormonal control of gametogenesis is not well defined among the species or even, between sexes. To increase the knowledge of gonadotropin hormones, we studied the trend by gene expression of gonadotropin receptors in the follicles and testis at different maturity stages in the European hake (Merluccius merluccius), a multiple-spawning species. With this aim, fshr and lhr were sequenced, characterized, and their gene expression was quantified in oocytes and in testes at different maturity stages. The deduced amino acid sequences were used to phylogenetic studies and evidenced that both receptors are phylogenetically closed to other gadoid species. The gene expression of both receptors was poorly expressed in primary follicles, increased in vitellogenic follicles and to later decrease in hydrated oocytes. In testis, highest levels of lhr were detected during spermiation, while levels of fshr were constant. For the first time, a histological analysis was performed in European hake testes showing an unrestricted lobular testis. To better elucidate the mechanisms involved in the oogenesis of the European hake, the expression of estrogen receptor and cyp19a was also investigated displaying high levels in all classes of follicles. All these data allow to increase the knowledge on reproductive physiology of an important socioeconomical species and it seeks to shed more light on the role of the receptors here studied during gametogenesis of multiple-spawning fish.     

Characterization,specificity and sensibility of produced anti-<Emphasis Type="Italic">Rhamdia quelen</Emphasis> vitellogenin in Brazilian fish species

Endocrine-disrupting chemicals (EDCs) are widespread used and can interfere on hormone regulation with adverse consequences for both biota and human. Vitellogenin (vtg) is a yolk precursor protein synthesized by the liver in response to estrogen. In order to characterize the vtg of tropical fish Rhamdia quelen and establish a molecular biomarker, adult male individuals were exposed to 17-β-estradiol (E₂) for vtg induction and anti-R. quelen vtg polyclonal antibodies production. Vitellogenic female fish were used as positive control group. E₂-induced vtg was characterized as a glycolipophosphoprotein of high molecular mass with peptide mass fingerprint very similar in E₂-exposed male and vitellogenic female fish. A polyclonal serum containing anti-R. quelen vtg antibodies was produced and showed high specificity and sensibility to detect the vtg of three fish species: R. quelen, Piaractus mesopotamicus and Prochilodus lineatus. Wildlife and laboratory studies reported that EDCs released into the environment may alter the levels of plasma vtg in male fish, making this protein a valuable biomarker of xenoestrogens exposure. Then, we propose the use of anti-R. quelen vtg as a tool for biomonitoring studies and water quality assessment in Brazil and South American countries where the three fish species occur.     

Effects of dietary <Emphasis Type="Italic">myo</Emphasis>-inositol on growth,chemical composition and plasma chemistry of Amur sturgeon <Emphasis Type="Italic">Acipenser schrenckii</Emphasis>

The present study was conducted to demonstrate the dietary myo-inositol requirement and its effects on the growth, proximate composition and blood chemistry of Amur sturgeon (Acipenser schrenckii). Triplicate groups of 30 fish (initial weight 11.90?±?0.12 g) were fed different diets containing graded levels of myo-inositol (28.75, 127.83, 343.83, 565.81, 738.15 and 936.28 mg kg^?1) until satiation for 56 days. The fish were weighed after a 24-h fast, and six fish were used for whole body composition analysis. Further, the liver and muscle were sampled from another six fish for lipid analysis. The blood and liver were sampled from the remaining six fish for haematology and fatty acid analysis. The weight gain of fish increased with myo-inositol content, from the 28.75- to 343.83-mg kg^?1 myo-inositol treatment groups, and then stabilised. The liver lipid content and hepatosomatic index decreased significantly from 21.91 to 19.14% and from 3.20 to 2.76% with increased dietary myo-inositol supplementation, respectively. The whole body lipid content generally decreased from 6.33 to 5.55%. The content of liver-saturated fatty acids decreased significantly (28.13%) in the 936.28-mg kg^?1 treatment group. The content of plasma non-esterified fatty acids increased with the increase in dietary myo-inositol supplementation from 0.77 to 1.17 mmol L^?1, whereas the content of triglycerides significantly decreased from 4.62 to 3.28 mmol L^?1. In conclusion, the optimum myo-inositol requirement was found to be 336.1 mg kg^?1, based on weight gain in a two-slope quadratic broken-line model.     

Molecular evolution of myoglobin in the Tibetan Plateau endemic schizothoracine fish (<Emphasis Type="Italic">Cyprinidae</Emphasis>, <Emphasis Type="Italic">Teleostei</Emphasis>) and tissue-specific expression changes under hypoxia

Myoglobin (Mb) is an oxygen-binding hemoprotein that was once thought to be exclusively expressed in oxidative myocytes of skeletal and cardiac muscle where it serves in oxygen storage and facilitates intracellular oxygen diffusion. In this study, we cloned the coding sequence of the Mb gene from four species, representing three groups, of the schizothoracine fish endemic to the Qinghai-Tibetan Plateau (QTP), then conducted molecular evolution analyses. We also investigated tissue expression patterns of Mb and the expression response to moderate and severe hypoxia at the mRNA and protein levels in a representative of the highly specialized schizothoracine fish species, Schizopygopsis pylzovi. Molecular evolution analyses showed that Mb from the highly specialized schizothoracine fish have undergone positive selection and one positively selected residue (81L) was identified, which is located in the F helix, close to or in contact with the heme. We present tentative evidence that the Mb duplication event occurred in the ancestor of the schizothoracine and Cyprininae fish (common carp and goldfish), and that the Mb2 paralog was subsequently lost in the schizothoracine fish. In S. pylzovi, Mb mRNA is expressed in various tissues with the exception of the intestine and gill, but all such tissues, including the liver, muscle, kidney, brain, eye, and skin, expressed very low levels of Mb mRNA (<?8.0%) relative to that of the heart. The trace levels of Mb expression in non-muscle tissues are perhaps the major reason why non-muscle Mb remained undiscovered for so long. The expression response of the Mb gene to hypoxia at the mRNA and protein levels was strikingly different in S. pylzovi compared to that found in the common carp, medaka, zebrafish, and goldfish, suggesting that the hypoxia response of Mb in fish may be species and tissue-specific. Notably, severe hypoxia induced significant expression of Mb at the mRNA and protein levels in the S. pylzovi heart, which suggests Mb has a major role in the supply of oxygen to the heart of Tibetan Plateau fish.     

Molecular cloning and expression analysis of <Emphasis Type="Italic">Megalobrama amblycephala</Emphasis> transferrin gene and effects of exposure to iron and infection with <Emphasis Type="Italic">Aeromonas hydrophila</Emphasis>

Transferrin (Tf) plays an important function in iron homeostasis and metabolism of organisms. In this study, we identified and characterized the Tf gene in Megalobrama amblycephala and evaluated its expression in basal conditions as well as after iron overload and experimental infection with Aeromonas hydrophila. Furthermore, we studied the iron binding properties of recombinant Tf. The full-length M. amblycephala Tf complementary DNA (cDNA) (GenBank accession no.: KX698308) of 2245 bp was cloned and contained a 1953 bp open reading frame (ORF) encoding 650 amino acid residues and flanked by a 68 bp 5′ and a 204 bp 3′ untranslated regions (UTR). Predicted conservative structure illustrated that M. amblycephala Tf consisted of two conservative Tf domains. Amino acid sequence alignment revealed that M. amblycephala Tf had high similarity with that of cyprinids deposited in Genbank, and phylogenetic analysis showed that M. amblycephala Tf clustered with Ctenopharyngodon idella and Hypophthalmichthys molitrix. Tissue expression pattern analyses demonstrated that the liver was the main Tf mRNA expressing organ, being significantly higher than other tissues (p < 0.05). In the liver, Tf mRNA expression in fish artificially injected with the pathogenic bacteria A. hydrophila was significantly upregulated, reaching a peak at 12 h post injection (hpi) and then decreasing afterward. The expression in FeCl₃-injected fish showed a similar tendency, but reached a peak at 8 hpi. Meanwhile, fish serum iron significantly decreased following A. hydrophila injection, but increased to peak at 4 hpi and then decreased in FeCl₃-injected fish. The recombinant M. amblycephala Tf showed iron binding capacity using CAS analysis. These results are helpful to understand the structure and regulation of expression of Tf, as well as the specific function of Tf for both immune responses and iron homeostasis.     

Environmental factors on virulence of <Emphasis Type="Italic">Aeromonas hydrophila</Emphasis>

Aeromonas hydrophila are known for being opportunistic pathogens, harboring various virulence factors and triggering lesions and death in fish. The disease caused by bacteria can make fish inappropriate for human consumption, besides representing a risk to public health. The pathogenesis can be influenced by environmental variables, affecting fish productivity and mortality. The present study aimed to determine whether A. hydrophila harbor the virulence genes aerolysin, hydrolipase, elastase, lipase, cytotonic enterotoxin (ast), lateral flagellum (laf), and polar flagellum (fla) and to evaluate the influence of environmental variables on in vitro growth, in vivo virulence and expression of some of these genes. Polymerase chain reaction (PCR)-based screening for the presence of these virulence genes was performed on 35 isolates. Six isolates containing different profiles of virulence genes were tested for in vitro growth under different conditions of pH, temperature, and ammonia and for in vivo virulence under these same environmental conditions. RT-qPCR was used to quantify the expression of aerolysin, lipase, and fla genes. All the tested environmental factors influenced the growth of A. hydrophila, while pH and ammonia concentrations influenced the bacterial virulence. The expression of the fla gene increased when bacteria were grown in higher ammonia concentration. The mortality established by Aeromonas is influenced by several environmental factors pinpointing the importance of its control in fish farming to avoid higher economic loses associated to bacterial disease outbreaks.     

Morphology,sex steroid level and gene expression analysis in gonadal sex reversal of triploid female (XXX) rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>)

In non-mammalian vertebrates, estrogens and expressions of cyp19a1 and foxl2 play critical roles in maintaining ovary differentiation and development, while dmrt1 and sox9 are male-specific genes in testicular differentiation and are highly conserved. In order to deeply understand the morphological change, sex steroids level and molecular mechanism of triploid female gonadal reversal in rainbow trout, we studied the ovary morphology, tendency of estradiol-17β (E2) and testosterone (T) levels and the relative expressions of dmrt1, cyp19a1, sox9 and foxl2 in juvenile and adult fish. Our results demonstrated that the development of triploid female gonads in rainbow trout went through arrested development, oocytes dedifferentiation, ovary reconstruction and sex reversal finally. During early gonadal development (154–334 days post-fertilization), the expressions of foxl2 and cyp19a1 increased linearly, while expressions of dmrt1 and sox9 were extremely suppressed, and E2 level was higher, while T level was lower. During the mid-to-late period of triploid female gonadal development (574–964 days post-fertilization), the expressions of dmrt1 and sox9 remained high and were very close to the quantity of diploid male genes, and T levels were even reaching diploid male plasma concentrations, while expressions of cyp19a1 and foxl2 were decreased, leading to decrease in E2 level. We realized that the development model of rainbow trout triploid female gonads was extremely rare, and the regulatory mechanism was very special. Genes involved in gonadal development and endogenous estrogens are pivotal factors in fish natural sex reversal.     

Dietary supplementation of yeast (<Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>) improves growth,stress tolerance,and disease resistance in juvenile Nile tilapia (<Emphasis Type="Italic">Oreochromis niloticus</Emphasis>)

The yeast Saccharomyces cerevisiae is one of the commonest probiotics incorporated in aquafeeds. An 84-day feeding trial was conducted to evaluate the effects of varying dietary inclusions of S. cerevisiae, 0% (control), 3% (YF3), 5% (YF5), and 7% (YF7), on growth, stress tolerance, and disease resistance in juvenile (body mass ~?21 g) Nile tilapia (Oreochromis niloticus). Fish were randomly distributed in groups of 20 into 12 1-m³ hapas and fed isoenergetic (~?17 kJ g^?1 gross energy) and isonitrogenous (~?300 g kg^?1 crude protein) diets at 3% of their bulk weight daily. Specific growth rates were significantly higher for the yeast-fed fish (0.77–0.78% day^?1) than for the control fish (0.60% day^?1) and resulted in significantly higher mean final weights for the yeast-treated groups. Protein and lipid retention efficiencies were also significantly higher in the yeast-fed fish than in the control group. In subsequent stress challenge trials, the yeast-fed fish had greater tolerance to acute heat as well as hypoxia exposure than the control fish. Survival rates of the yeast-treated groups following sudden exposure to elevated water temperature (40 °C) ranged from 82.5 to 100% compared to 15% for the control. Mean survival rates following a 24-h hypoxia exposure were also generally significantly higher for the yeast-fed fish. The probiotic groups recorded a relative percent survival (RPS) of 75% after a 14-day Aeromonas hydrophila infection challenge. The results of this study indicate that S. cerevisiae as an additive in Nile tilapia diets has beneficial impacts on growth, stress tolerance, and disease resistance.     

Microalga <Emphasis Type="Italic">Isochrysis galbana</Emphasis> in feed for <Emphasis Type="Italic">Trachinotus ovatus</Emphasis>: effect on growth performance and fatty acid composition of fish fillet and liver

Seeking alternatives to the depleting fish oil are crucial for marine fish aquaculture, which is currently dependent on fish oil as the primary source of n-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFAs). Five isonitrogenous (46% crude protein) and isolipidic (16% crude lipid) feed diets (FO, ISO2.9, ISO4.8, ISO6.7, ISO8.6) were formulated by partially replacing fish oil with microalgae Isochrysis galbana. These diets were fed to triplicate tanks of Trachinotus ovatus (mean initial weight 1.92 g) for 80 days. This work demonstrates that a moderate inclusion (around 4.5–5.0 wt%, equivalent to the replacement of 24–26 wt% fish oil) of I. galbana biomass in fish diet improves fish growth performance, lipid deposition and enhances total n-3 fatty acids, DHA, and EPA contents in neutral and polar lipids (PLs) of fish muscle and liver of T. ovatus. The results disclosed in this study suggest that I. galbana microalgae represents a potential high-quality substitute for fish-based ingredients in aquaculture feeds, which can be a promising sustainable solution to resolve the depleting fish oil resource in a cost-effective manner.