Marine Carnivorous Fish Research Articles

Impact of the diet in the gut microbiota after an inter-species microbial transplantation in fish

Inter-species microbial transplantations offer the possibility of transferring species-specific microbes and their associated functionality. As a conceptual approach, an intestinal microbiota transplant (IMT) between two marine carnivorous fish species that thrive in different environmental conditions was conducted: from donor Atlantic salmon (Salmo salar) to recipient gilthead seabream (Sparus aurata), after obliterating its basal microbiota with an antibiotic treatment. To confirm that the gut microbiota was able to recover after antibiotics without the influence of the diet, a group of gilthead seabream not submitted to the IMT was kept fasted as an internal control. To assess the effect of the diet after the IMT, two groups of gilthead seabream were respectively fed with their typical diet and with Atlantic salmon diet. At 36 days post-IMT, the gut of the individuals fed with their typical diet was dominated by the feed-associated bacteria, while those fed with the salmon diet had developed a unique microbiota from the convergence of the diet, donor, and recipient microbiota. These results suggested that an intestinal microbiota transplantation may be effective if the basal microbiota from the gut is first cleared and a targeted dietary modification is provided to maintain and enrich the novel bacteria species over time.

Daidzein improved glucose homeostasis via PI3K/AKT and modulated the communities of gut microbiota in turbot (Scophthalmus maximus L.)

The glucose intolerance of fish limits its carbohydrate utilization. It is of practical significance to improve the glucose tolerance of fish, especially carnivorous fish in aquaculture. Daidzein, one of the most abundant soy isoflavones in legumes, has been proved to have positive effects on glucose homeostasis. In present study, the effects of daidzein on glucose tolerance and hepatic glucose metabolism were investigated in marine carnivorous fish turbot (Scophthalmus maximus L.). The results of oral glucose tolerance test found that oral administration of daidzein improved the glucose tolerance of turbot and promoted the insulin secretion in the serum of turbot. In vitro, daidzein promoted glucose consumption, suppressed hepatic glucose production and improved insulin sensitivity in primary hepatocytes. Then, both in vivo and in vitro studies found that daidzein activated phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway. While blocking PI3K/AKT signaling pathway with PI3K inhibitor, the beneficial effects of daidzein on hepatic glucose metabolism in primary hepatocytes were abolished. Besides, oral administration of daidzein significantly altered the microbiota profiles, which increased the abundance of Bacteroidota, decreased the ratio of Firmicutes/Bacteroidota and the abundance of potential pathogen such as Ralstonia and Pseudomonas. In conclusion, daidzein improved glucose homeostasis via PI3K/AKT signaling pathway, and the intestinal microbiota might also be involved in this process.

Dietary glutamine enhances growth performance and gut integrity of Totoaba macdonaldi juveniles fed low fishmeal diets but has limited synergetic effects in combination with a prebiotic

Fishmeal (FM) replacement using cost-effective blends of complementary ingredients is commonly used in carnivorous marine fish diets for economic and sustainable purposes. The use of functional compounds such as prebiotics or functional ingredients is a nutritional strategy in low FM diets to maximize growth and feed utilization, as well as reducing enteropathies caused by plant proteins, in particular soybean meal (SBM) that can induce enteritis in Totoaba macdonaldi juveniles. Therefore, this study was conducted to evaluate the effects of glutamine (Gln) and agavin (AGA) as a novel prebiotic or a combination of both on growth parameters, digestive capacity, whole-body proximate composition, gut health, and sustainable and economic indexes in totoaba juvenile fed low FM (17%) diet for 56 days. Juvenile totoaba with an initial weight of 168 ± 4 g were fed one of four isoproteic and isolipidic diets formulated with poultry by-product meal and FM in a 2:1 ratio and 24% of SBM. For the control basal diet (SBM), no Gln or AGA was added. The other three experimental diets consisted of the basal diet with either 1.5% glutamine (GLN), 1% prebiotic agavin (AGA), or 1.5% glutamine and 1% agavin (Gln + AGA) supplementation. Fish fed the Gln diet significantly improved growth, feed utilization and increased trypsin, total alkaline proteases, and L-aminopeptidase activities. Additionally, an enhanced brush border height (BBH) in the distal intestine was observed in the Gln group, suggesting improved intestinal health compared to the rest of the treatments. However, no significant synergistic effect was observed in fed fish the Gln + AGA diet. Interestingly, no signs of enteritis among the fish fed the four experimental diets was observed. These results suggest that fish with an initial size of 168 g are less susceptible to the adverse effects of SBM compared to previous studies. The inclusion of 1.5% dietary glutamine is recommended in totoaba diets with low FM containing 24% of SBM. Since the fish fed the diet supplemented with glutamine + agavin resulted in intermediate values for the parameters evaluated, it is recommended to evaluate different levels of agavin in combination with glutamine or perform longer bioassays using immunological or environmental challenges to aid in elucidating potential benefits of these functional compounds and their synergistic effects.

A comparative study of dietary lipid sources on growth performance, body composition, fillet quality, and nutrient retention in juvenile yellow drum (Nibea albiflora)

Vegetable oils (VOs) are promising alternatives for fish oil (FO) in the aquafeed industry. However, high dietary VOs lead to undesirable effects on fish growth performance and health, but little information is known about VOs on fillet quality and nutrient retention. This study compared the impacts of different VOs on fish growth performance, fillet quality, and nutrient retention in juvenile yellow drums (Nibea albiflora). The FO group was used as the control (containing 6% FO), and the other four diets had the same lipid content with 5% FO was substituted by different VOs(soybean oil [SO], linseed oil [LO] rapeseed oil [RO], and palm oil [PO]). Juvenile fish (initial body weight of 5.55 ± 0.02 g) were fed the respective diets for 56 days. Results indicated the replacement of FO by VOs was feasible without affecting the growth performance, body composition, or serum biochemicals. The SO diet significantly increased fillet yield and fillet calcium (Ca) and phosphorus (P) element contents. The PO diet reduced water-holding capacity, and altered fillet texture, but significantly increased fillet n-3 LC-PUFAs retention. This could be attributed to the preferential oxidation of SFAs therefore selectively retained DHA in the fillet. Fillet transcriptome sequencing analysis revealed that compared with the FO group, the upregulated mRNA levels of lipid transport-related genes were found in the SO (fabp4, and cd36) and PO (fabp4, cd36, lcat, acbp, and cav1)groups, whereas lipid synthesis-related (acss, elovl4, acsbg, acsl, and elovl1) and lipolysis-related genes (mgll, hsl, acaa1, abhd5, decr1, acad9, pparα, and cpt1) expression were upregulated in the RO and PO groups, respectively. Weighted gene co-expression network analysis clustered two coexpression modules. One module was significantly and positively correlated with fillet yield (P = 0.01, R = 0.64) and Ca element retention (P = 0.05, R = 0.51), and contained genes related to fillet development (eno3 and tnnt3) and Ca regulation (dhrs7c, mcam, and ocam). The other module included genes related to lipid metabolism (elovl1, scd, tecr, fbn1, thbs1, and mdh1), which was associated with fillet n-3 LC-PUFAs retention. Collectively, these findings demonstrated that SO, LO, RO, and PO can be utilized as alternative lipid sources for FO. Based on transcriptome analysis results, genes related to fillet development, Ca regulation, and lipid metabolism were highlighted. These findings help to understand the relationship between dietary lipid sources and fillet nutrient retention in marine carnivorous fish species.

Determination of dietary essential fatty acids in a deep-sea fish, the splendid alfonsino Beryx splendens: functional characterization of enzymes involved in long-chain polyunsaturated fatty acid biosynthesis

The splendid alfonsino Beryx splendens is a commercially important deep-sea fish in East Asian countries. Because the wild stock of this species has been declining, there is an urgent need to develop aquaculture systems. In the present study, we investigated the long-chain polyunsaturated fatty acid (LC-PUFA) requirements of B. splendens, which are known as essential dietary components in many carnivorous marine fish species. The fatty acid profiles of the muscles, liver, and stomach contents of B. splendens suggested that it acquires substantial levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from its natural diet. The functional characterization of a fatty acid desaturase (Fads2) and three elongases (Elovl5, Elovl4a, and Elovl4b) from B. splendens confirmed their enzymatic capabilities in LC-PUFA biosynthesis. Fads2 showed Δ6 and Δ8 bifunctional desaturase activities. Elovl5 showed preferential elongase activities toward C18 and C20 PUFA substrates, whereas Elovl4a and Elovl4b showed activities toward various C18-22 substrates. Given that Fads2 showed no Δ5 desaturase activity and no other fads-like sequence was found in the B. splendens genome, EPA and arachidonic acid cannot be synthesized from C18 precursors; hence, they can be categorized as dietary essential fatty acids in B. splendens. EPA can be converted into DHA in B. splendens via the so-called Sprecher pathway. However, given that fads2 is only expressed in the brain, it is unlikely that the capacity of B. splendens to biosynthesize DHA from EPA can fulfill its physiological requirements. These results will be useful to researchers developing B. splendens aquaculture methods.

Nutrient digestibility and enzyme activity of microbial floc, Tetraselmis chuii, and Spirulina platensis fed on Juvenile Cobia (Rachycentron canadum)

Cobia is a relatively new species of marine carnivorous fish with high aquaculture potential because of its fast growth (4-6 kg in a year) and ability to adapt and reproduce in the cultivation environment. This study aims to evaluate the nutrient digestibility and enzyme activity of cobia juveniles fed pelleted feed with microbial floc meal (MF), microalga Tetraselmis chuii (MT) meal, and microalga Spirulina platensis (MS) meal. Fish were fed pellets twice a day at satiation. The results showed that MS feed had higher and significantly different (p<0.05) of protein digestibility, enzyme activity, amylase and lipase, glycogen and lipid in the liver of juvenile cobia than MF feed. These two raw materials generally had no negative effect on cobia juvenile growth. Conversely, the value of nutrient digestibility and enzyme activity of MT feed could not be determined because the fish did not consume the feed.

Survival Rate Lemon Fish (Rachycentron canadum) Larvae in Lampung Marine Aquaculture Center

Cobia fish (Rachycentron canadum) is one of the marine carnivorous fish that is relatively new and has the potential to be cultuvited. This study aims to determine the effectiveness of larval rearing and nursery cobia fish found in the Center for Marine Aquaculture (BBPBL) Lampung. Held 20 January to 19 February 2021. The mature fish were mated in a 2x2x1 m concrete tank filled with 4,000 L of water. The eggs produced were harvested using an egg collector, counted and hatched in a 0.8x0.6x0.5 m aquarium. After hatching, the larvae were moved into nursery tanks with a density of 5-7 fish/liter. Larvae were reared until they were 25 days old and fed naturally with Branchionus sp, Nannochloropsis sp, and artemia. The larvae were then counted, weighed, measured, graded and their growth analyzed. The results of this study showed that not all of these cobia eggs were fertilized by male cobia sperm at the time of spawning. Spawning was carried out on January 16, 2022. Total eggs was 648,000, total fertilized eggs was 480,000 and fertilization rate was 74.04 %. The results of the initial larval count were 75,000, 17,040 were harvested with a survival rate of 22.72%. Water quality (pH, DO, temperature, salinity, nitrite and ammonia) during the research was still normal.

The Effects of Dietary Cottonseed Oil on Growth Performance of Juvenile Red Drum (Sciaenops ocellatus L.) and Hybrid Striped Bass (Morone chrysops × M. saxatilis S.)

Various cottonseed products containing higher levels of protein and lipid than traditional cottonseed meal have been evaluated in recent years with several carnivorous marine fish species. In previous studies in this laboratory, distinct differences in the acceptability of diets containing those cottonseed products were noted for red drum and hybrid striped bass. Therefore, the present study consisted of two concurrent feeding trials in which the effects of increasing levels of dietary cottonseed oil were evaluated with both juvenile red drum and hybrid striped bass. Three experimental diets were formulated to contain either 0, 2, or 4% of cottonseed oil in place of menhaden fish oil. All diets were formulated to contain approximately 9% lipid, with that of the basal diet (0% cottonseed lipid) primarily contributed by menhaden fishmeal and menhaden oil. In concurrent trials, each diet was fed twice a day to triplicate groups of juvenile red drum and hybrid striped bass initially averaging 1.86 g/fish and 1.41 g/fish, respectively, for 6 weeks. Results of the feeding trial showed that there were no significant differences among red drum fed the different dietary treatments based on growth parameters (weight gain and feed efficiency) or whole-body proximate composition. On the contrary, hybrid striped bass showed significant ( P ≤ 0.05 ) differences in responses to the dietary treatments with weight gain decreasing as the inclusion levels of cottonseed oil increased while their hepatosomatic index significantly increased. Thus, results of this study showed distinctly different responses of red drum and hybrid striped bass to increasing levels of dietary cottonseed oil, with hybrid striped bass being much more sensitive than red drum in terms of reduced weight gain and altered body condition which appeared to be related to reduce diet palatability from cottonseed oil.

A comparison of regression models for defining EPA + DHA requirements using the gilthead seabream (Sparus aurata) as a model species

Carnivorous marine fish species such as gilthead seabream (Sparus aurata) require dietary eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids for optimal growth and wellbeing. The rapid growth of global aquaculture, along with increased proportions of dietary oil to increase growth rate of farmed fish, has meant that the supply of marine oils used in aquafeeds has become limited. The shortfall has been satisfied by using vegetable oils that lack EPA and DHA and, therefore, EFA (essential fatty acid) requirements of juvenile marine fish require reassessment. A dietary trial was carried out with gilthead seabream (~25 g) that were fed diets with six EPA + DHA levels ranging from 0.2% - 3.2% diet as fed. For each pellet size, the biometric data (weight gain, daily growth index and feed conversion ratio) were analysed by four different regression strategies, namely split linear, quadratic, the Gompertz function, and the four-parameter logistic function. Over the whole experimental period (two pellet sizes) data suggested the current published requirement (1% of diet) was low and should be increased to at least 1.2%. However, when the first pellet size for fish of 25–80 g was considered, the apparent requirement was at least 1.4% of diet. This demonstrated in a single trial that EFA requirement was a function of fish mass, decreasing as the fish grows. If FCR is considered, the requirement may be as high as 2%. The suitability of different regression models varied, as the data for the first pellet was best fit by curves but, over both pellet sizes, the split linear fit the data best. For asymptotic models (Gompertz and four-parameter logistic functions), a novel way of defining the requirement was presented, the “elbow” calculation as a method to bisect an asymptotic function. Therefore, using the raw data, we illustrate how a range of regression approaches could be explored when determining nutrient requirement estimates as no single model was an ideal fit for all response curves.

Long-Chain Polyunsaturated Fatty Acids n-3 (n-3 LC-PUFA) as Phospholipids or Triglycerides Influence on Epinephelus marginatus Juvenile Fatty Acid Profile and Liver Morphophysiology.

Simple SummaryFish feeding is responsible for almost 60% of the total cost of marine fish production, so nutritional studies are always in demand. Dusky grouper is a promising species for aquaculture, but studies of the species’ nutrition are still lacking. The present study investigated the effects of fatty acids, provided as different lipid classes in four different diets, for Epinephelus marginatus fingerlings and evaluated their physiological and morphological responses in order to provide new insights about grouper nutrition. The fatty acids, provided as different lipid classes, modified the physiological and morphological responses of E. marginatus, showing that the inclusion of these lipids as different classes should be considered in order to obtain better results in terms of fish fillet quality. These results provided valuable insights into the nutrition and physiology of dusky groupers, helping to pave the way for the establishment of this fish species as a produced species worldwide.Phospholipids (PL) are membrane components composed of fatty acids (FA), while triglycerides (TG) are a main source of energy and essential FA. Polyunsaturated FA (PUFA), such as docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA), are essential for marine carnivorous fish; thus, an 8-week experiment was performed to evaluate the influence of DHA and EPA, provided as PL and TG, on the morphophysiology of Epinephelus marginatus juveniles. A basal diet was manufactured, and DHA and EPA in PL form (PL1—low amount PL2—high amount) and TG form (TG1—low amount; TG2—high amount) were added. Dusky grouper juveniles were equally distributed in 12 tanks of 20 animals each, and liver and muscle were sampled for metabolic analysis. The total hepatic lipids in PL1 and PL2 were higher when compared to the initial, TG1 and TG2 groups. Total lipids in muscle were higher in PL2 and TG1 than PL1 and TG2, respectively. Diets rich in DHA and EPA in PL and TG resulted in higher deposition of these FA in the muscle polar fraction. However, fish fed diets containing lower amounts of DHA and EPA in PL and TG stored those in the muscle neutral fraction and liver, centralizing the storage of DHA and EPA.

Distribution of Anisakidae Family Infected Marine Fish in Indonesia

Background: Family of Anisakidae is one of the zoonotic helminth parasitics. The distribution of the family Anisakidae is extensive. It needs to be known because the diversity of parasites can provide information about the distribution area and impact of the parasites of the family Anisakidae in Indonesia. This review article summarises the distribution of parasites from the family Anisakidae that infects marine fish and the factors that influence Indonesia. Methods: This research is qualitative research through literature study as the main object. The data from the literature study results are presented in tables and figures then explained descriptively. Results: The distribution of Anisakidae in Indonesia is found in four genera, namely the genus Anisakis, Pseudoterranova, Terranova and Contracaecum, which are mostly found from the carnivorous marine fish of the family Balistidae, Carangidae, Epinephelidae, Lutjanidae, Priacanthidae, and Scombridae Conclusions: Four genera of endoparasitic worms from the Anisakidae family were reported to infect Indonesian marine fish, including Anisakis, Pseudoterranova, Terranova and Contracaecum. Temperature, salinity, hosts' presence, and anthropogenic factors are biotic and abiotic factors that can affect the distribution of Anisakidae. The information on this literature study results is hoped to be used as the basis for developing research in fish parasitology in particular and increasing public awareness of fish processing in general.

Dietary polystyrene nanoplastics exposure alters liver lipid metabolism and muscle nutritional quality in carnivorous marine fish large yellow croaker (Larimichthys crocea)

Nanoplastics (NPs) cause various adverse effects on marine fish. However, effects of dietary NPs exposure on liver lipid metabolism and muscle nutritional quality of carnivorous marine fish are not fully understood. In this study, a 21-day feeding test was conducted to simulate the food chain transfer of polystyrene nanoplastics (PS NPs) and then evaluate effects of different dietary PS NPs levels on the survival, growth performance, liver lipid metabolism, and muscle nutritional quality of large yellow croaker Larimichthys crocea. Results indicated that the survival and growth of large yellow croaker decreased with the increase of PS NPs levels. Moreover, PS NPs induced excessive liver lipid accumulation by down-regulating the expression of lipolysis-related genes and inhibiting the AMPK-PPARα signaling pathway. In vitro, PS NPs could be accumulated in hepatocytes, reduce cell viability, and disrupt lipid metabolism of hepatocytes. Also, we found for the first time that PS NPs altered fatty acid composition and texture of fish muscle by enhancing oxidative stress and disrupting lipid metabolism. Overall, this study indicated that PS NPs induced liver lipid deposition by inhibiting lipolysis, and demonstrated that PS NPs altered the nutritional quality of fish, which might cause potential health effects for human consumers.

Evaluation of different dietary n ‐3 lc‐pufa on the growth, intestinal health and microbiota profile of golden pompano ( Trachinotus ovatus )

The omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA), such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), are essential fatty acids for marine fish. This study aimed to evaluate different dietary n-3 LC-PUFA on the growth, intestinal health and microbiome in carnivorous marine fish Trachinotus ovatus. Three diets, respectively, supplemented with fish oil, EPA-enriched oil and DHA-enriched oil were fed juvenile T. ovatus for 10 weeks. The results showed that the three groups showed no difference in the growth, histology and digestive enzyme activities of anterior intestine. Moreover, the intestinal ACP and ALP activities and tnfɑ mRNA level were increased in the EPA-enriched group, whereas the serum diamine oxidase activity and intestinal lysozyme activity and malondialdehyde content were decreased in both EPA- and DHA-enriched groups. Meanwhile, these two diets also down-regulated the mRNA expression of Mucin 2, Mucin 13, hes1-b, Krueppel-like factor 4 and Occludin, and up-regulated the zonula occludens-1 mRNA levels in intestine. Moreover, the two groups significantly decreased the intestinal Vibrio abundance and increased the probiotic proportions, especially in the EPA-enriched group. These results indicate dietary n-3 LC-PUFA would facilitate normal intestinal function and probiotics profiles of T. ovatus, and the EPA-enriched group appears to be more positive.

Characterization of digestive enzymes during early ontogeny of white Snook (Centropomus viridis).

The white snook (Centropomus viridis) is a species with great aquaculture potential, therefore, the present study aims two objectives; 1) to characterize digestive enzymatic activity during larval development and; 2) characterize the diversity and functionality of digestive enzymes in an early juvenile stage of C. viridis. On first feeding, larvae were 2.75 ± 0.09 mm total length and grew to 24.35 ± 4.35 mm after 42 days. The specific activity of acid proteases was detected with low activity from day 1 (Days after hatching, DAH) to day 21, and increased at 23 DAH, reaching maximum activity at 40 DAH. Meanwhile, digestive enzymatic activity of alkaline proteases was observed from hatching to day 40. From hatching until 40 DAH, the presence of alkaline proteases, trypsin, chymotrypsin, leucine aminopeptidase, α-amylase and lipase were detected with different activity patterns. Total and specific activity of digestive enzymes on juveniles showed higher activity of acid than alkaline proteases, while α-amylase had a higher activity than lipases. The maximum activity of acid proteases was observed at 40 °C and at pH 2.0, while digestive alkaline proteases showed maximum activity at 60 °C. α-amylases and lipases showed their maximum activities at 50 °C. The maximum alkaline protease and α-amylase activities were found at pH 7 to 9. The enzymatic activity of juvenile's acid proteases was highly inhibited by Pepstatin A (96%), however the activity of alkaline proteases incubated with PHEN, TLCK, SBTI, PMFS, and OVO showed reductions of 51.29, 30.16, 27.98, 27.26, and 24.68% respectively. Lipase activity was totally inhibited with Ebelactone B, and highly inhibited by Ebelactone A, Orlistat, 1% SDS, and PMFS (96.12, 77.16, 64.22, and 51.29%, respectively). Seven bands (102.6, 65.7, 58.9, 40.6, 27.4, 21.5, and 15.8 kDa) resolved by protein electrophoresis were detected with alkaline protease activity, identified as serine proteases and metalloproteases, and three bands (57, 43.9, and 32.6 kDa) with lipase-like activity were also identified. These results show that C. viridis ontogeny entails an indirect development of its digestive system with a functional stomach on day 23, and characterized by increases in pepsin activity. Indeed, white snook ontogeny shows a similar developmental trajectory to other carnivorous marine fish, showing a diversity of alkaline proteases that work in a wide range of pH and temperatures. Thus, the identification of these enzymes provides advantages to formulate white snook aqua-feeds.

ITRAQ-based quantitative phosphoproteomics provides insights into the metabolic and physiological responses of a carnivorous marine fish (Nibea albiflora) fed a linseed oil-rich diet

The limited production of fish oil (FO) cannot meet the increasing demand of the aqua-feed industry. Accordingly, the replacement of FO with sustainable alternatives such as vegetable oils has become imperative. Linseed oil (LO), which has an abundance of α-linolenic acid (ALA), is a promising FO alternative. Nevertheless, high dietary LO inclusion generally causes abnormal hepatic lipid accumulation and growth retardation across carnivorous marine fish species. Previous studies have attempted to elucidate the mechanisms with regard to gene and protein levels; however, little is known about posttranslational modifications. In the present study, iTRAQ phosphoproteomics was conducted to investigate the metabolic and physiological responses of the yellow drum (Nibea albiflora) fed an LO-rich or FO-rich diet. Identification and analyses of differentially abundant phosphorylated proteins in hepatic tissue were conducted with parallel reaction monitoring (PRM) verification in reference to the genome sequences of the yellow drum. Among the specific peptides that passed the threshold, 203 hyperphosphorylated and 182 hypophosphorylated peptides were identified. Several functional categories and pathways were associated with these proteins that were mostly related to lipid, amino acid, and carbohydrate metabolism. In particular, the AMP-activated protein kinase (AMPK) pathway, mechanistic target of rapamycin (mTOR) pathway, and citrate (TCA) cycle are discussed. Statement of significanceDietary LO caused abnormal hepatic lipid accumulation and retarded growth performance. The abnormal hepatic lipid accumulation in the fish fed the LO-rich diet might have arisen from AMPK signaling pathway-mediated de novo synthesis of fatty acids and the synthesis of phospholipids. An mTOR signaling pathway-mediated reduction in ribosome protein synthesis could have been a factor in the growth retardation. Changes in UPS and autophagy proteins phosphorylation and aminotransferase activity levels were related to the flux of amino acids into the TCA cycle for ATP production. The results of PRM were highly correlated with the phosphoproteomics results. These findings will contribute to a better understanding of the mechanisms of abnormal hepatic lipid accumulation and retarded growth performance in carnivorous marine fish fed linseed oil-rich diets.

Effects of complete replacement of fish oil with plant oil mixtures and algal meal on growth performance and fatty acid composition in juvenile yellowtail Seriola quinqueradiata

Docosahexaenoic acid (DHA) is an essential fatty acid for marine carnivorous fish. Algal meal (AM), available as a new dietary DHA source, could completely replace dietary fish oil (FO). In this study, dietary FO was replaced with plant oil mixtures and AM in juvenile yellowtail Seriola quinqueradiata to investigate its effects on growth performance and fatty acid composition. The FO control diet was prepared with only pollack liver oil as the lipid source. For the non-FO diets, pollack liver oil was completely replaced with mixtures of canola oil and palm oil, with AM supplementation at 0% (AM0), 1% (AM1), 2% (AM2), 3% (AM3), and 4% (AM4). After completion of the 8-week feeding trial, the AM2 group showed significantly higher values for final body weight and feed efficiency than the AM0 group. No significant differences were observed in the other parameters of growth performance. Whole-body fatty acid composition reflected the dietary fatty acid composition in all dietary groups. These findings demonstrate that AM is useful as a DHA source in yellowtail aquaculture, thus contributing to a reduction in the use of FO in fish diets.

Housefly (Musca domestica) Larvae Preparations after Removing the Hydrophobic Fraction Are Effective Alternatives to Fish Meal in Aquaculture Feed for Red Seabream (Pagrus major)

Insects are an attractive alternative to fish meal (FM) as a sustainable protein source in aquaculture feed that does not negatively impact the marine ecosystem. Despite housefly (Musca domestica) larvae having adequacy of amino acid profiles, they have sometimes been reported to be inferior to FM, especially for marine carnivorous fish species. Here, we report that the removal of the hydrophobic fractions from housefly larvae enables significant replacement of FM in the diet of the red seabream (Pagrus major). In a feeding trial, housefly (HF) larvae that had the hydrophobic fraction removed as a complete substitution for 70% FM produced satisfactory growth. However, HF larvae that were supplemented with the hydrophobic fraction resulted in significant growth reduction. Growth recovery was incomplete by supplementation of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) to undefatted HF larvae, being equivalent to that of fatty acid content with a control diet. Moreover, fish with a dietary intake of catechol identified from the hydrophobic fraction of the HF showed growth reduction and morphological alterations in the intestine. Our findings indicate that the hydrophobic fraction from HF larvae contains a negative factor for fish growth and eliminating the fraction from HF larvae is thought to be an important process for sustainable aquaculture.

Effects of dietary lipid sources on the intestinal microbiome and health of golden pompano (Trachinotus ovatus)

Replacement of fish oil (FO) with vegetable oils (VO) in diets is economically desirable for the sustainable development of the aquaculture industry. However, inflammation provoked by FO replacement limited its widely application in fish industry. In order to understand the mechanism of VO-induced inflammation, this study investigated the impact of different dietary vegetable oils on the intestinal health and microbiome in carnivorous marine fish golden pompano (Trachinotus ovatus). Three diets supplemented with fish oil (FO, rich in long-chain polyunsaturated fatty acids), soybean oil (SO, rich in 18:2n-6) and linseed oil (LO, rich in 18:3n-3), respectively, were fed on juvenile golden pompano for 8 weeks, and the intestinal histology, digestive enzymes activities, immunity and antioxidant indices as well as intestinal microbiome were determined. The results showed that dietary SO significantly impaired intestinal health, and decreased the number and height of intestinal folds, and muscle thickness, as well as the zonula occludens-1 (zo-1) mRNA expression in intestine. Moreover, the two dietary VO significantly decreased the amylase and lipase activities in intestine, and reduced the trypsin activity in the dietary SO group. Furthermore, the two VO diets increased intestinal acid phosphatase (ACP) activity, while intestinal lysozyme (LZM) activity and serum diamine oxidase (DAO) activity in the SO group were also significantly increased (P < 0.05). Analysis of the intestinal microbiota showed that the two VO diets significantly increased the abundance of intestinal potentially pathogenic bacteria (Mycoplasma and Vibrio) and decreased proportions of intestinal probiotics (Bacillus and Lactococcus), especially in the dietary SO group. These results indicate that complete replacement of FO with VO in diets would induce intestinal inflammation and impair intestinal function, which might be due to changes in intestinal microbiota profiles, and that dietary SO would have a more negative effect compared to dietary LO on intestinal health in T. ovatus.

Effects of replacing fish oil with wheat germ oil on growth, fat deposition, serum biochemical indices and lipid metabolic enzyme of juvenile hybrid grouper (Epinephelus fuscoguttatus♀ × Epinephelus lanceolatus♂)

Fish oil was one of most important feed ingredients for carnivorous marine fish species, but the production might not cover all the necessary quantity for aquaculture. Meanwhile wheat germ oil could be a potential alternative for fish oil in aquatic feed. Hence, a 70 day feeding trial was conducted to investigate the effects of dietary fish oil replaced by wheat germ oil (WGO) on the growth, lipid and fatty acids deposition, and lipid metabolic enzymes activities of juvenile hybrid grouper (initial weight 55.31 ± 0.68 g), E. fuscoguttatus♀ × E. lanceolatus♂. Six isonitrogenous and isoenergetic experimental diets were formulated with 0%, 20%, 40%, 60%, 80% and 100% replacement of fish oil by WGO. Survival rate, weight gain rate, specific growth rate, and feed conversion ratio were similar among fish fed with different diets. Viserosomatic index and mesenteric fat ratio were significantly increased by dietary WGO. No significant differences were observed in the compositions of whole body, muscle and liver. C18: 3n-3 and C18:2n-6 contents in tissues were significantly increased, but EPA and DHA were significantly decreased by dietary WGO. No significant differences were found on the activities of hepatopancreas lipoprotein lipase, hepatic lipase and fatty acid synthase, while the activity of intestinal lipase was decreased. Total cholesterol, high density lipoprotein cholesterol, and low density lipoprotein cholesterol in plasma were not affected, but triglyceride was increased by dietary WGO. It can be concluded from the results that about 71.8% dietary fish oil can be replaced by WGO in diets with 50% crude protein and 12% crude lipid for subadult hybrid grouper, and fatty acids deposition and biosynthesis of this species was quite different from that of other fish species.

Molecular cloning and functional characterization of elongase (elovl5) and fatty acyl desaturase (fads2) in sciaenid, Nibea diacanthus (Lacepède, 1802)

In the present paper, we investigated the molecular cloning and functional characterization of elongase of very long chain fatty acid (elovl) and fatty acyl desaturase (fads) genes in a marine teleost, Nibea diacanthus. The elongase cDNA sequence encoded a polypeptide of 294 amino acids exhibiting Elovl5 activity, which effectively elongated both C18 (18:2n−6, 18:3n−3 and 18:3n−6) and C20 (20:4n−6 and 20:5n−3) polyunsaturated fatty acids. The desaturase cDNA sequence specified a polypeptide of 445 amino acids indicating Δ6 desaturation activity, which coul converted C18:2n−6 and C18:3n−3 to C18:3n−6 and C18:4n−3, respectively. Tissue distribution analysis by quantitative real-time PCR revealed that the elovl5 was primarily expressed in intestine and liver, while the fads2 was mainly expressed in liver and brain. These results increase our knowledge of the ability of endogenous highly unsaturated fatty acids (HUFA) biosynthesis in marine carnivorous fish.