Cobia Research Articles

A review on cobia, Rachycentron canadum, aquaculture

AbstractCobia, Rachycentron canadum, is an important species for aquaculture worldwide. Production technology from egg to market was established in the early 1990s and continues to be perfected to this day. This species exhibits extraordinary scope for growth and can reach between 4 and 8 kg in 1 year, with females growing almost twice as fast and large as males. Despite continuous progress in maturation, spawning, larval rearing, fingerling production, nutrition, health management, genetics, and growout technology, overall cobia aquaculture production worldwide has been slow in the last decade. One of the biggest challenges remains the development of practical commercial feeds that are ecologically and economically efficient for this species. Feed conversion ratios are still very high, ranging from 2.0 to 3.0:1. In addition to nutritional challenges, diseases such as Photobacterium, Amyloodinium ocellatus, and Brooklynella hostilis continue to impact cobia aquaculture production worldwide. Genetics and breeding programs for cobia are still at their infancy. We report on current status of cobia breeding efforts as well as on advances on developing female monosex populations to exploit the sexually dimorphic growth in this species. Nutrition, health, and genetics will be the greatest drivers to improve overall performance and increases in production of the cobia aquaculture industry.

Probiotic Potential of Indigenous (Bacillus sp. RCS1, Pantoea agglomerans RCS2, and Bacillus cereus strain RCS3) Isolated From Cobia Fish (Rachycentron canadum) and Their Antagonistic Effects on the Growth of Pathogenic Vibrio alginolyticus, Vibrio harveyi, Streptococcus iniae, and Streptococcus agalactiae

Large-scale fish farming faces many environmental stresses, which affect their immune systems, growth performance, and physiological homeostasis, resulting in increase in their susceptibility to infections. Some of the most common bacterial infections of cobia fish (Rachycentron canadum) include streptococcosis, vibriosis, furunculosis and mycobacteriosis, and pastelleurosis. Probiotics could be helpful in reducing or limiting the incidence of severe disease infections or outbreaks. Therefore, the present study aimed to isolate the indigenous bacterial species from healthy cobia fish and then selected 3 strains, including Bacillus sp. RCS1 (MW560712), Pantoea agglomerans RCS2 (MW560713), and Bacillus cereus RCS3 (MW560714) from the gut of juvenile’s cobia having advantageous assets or positive characteristics. Their analysis indicated the presence of similar biochemical profiles and all could effectively utilize carbon sources. The biosafety assessment did not show any pathological symptoms after 10 days of injecting the fish with isolated bacteria. The results showed that all the isolated bacteria in the present study had low auto-aggregation capacity within the first 3 h of incubation. The isolated bacteria showed strong tolerance when exposed to a range of pH. Although asymmetrically, a slow rise in the growth of isolated bacteria was observed within the pH range of 1–8 for RC1, 1–7 for RC2, and 1–6 for RC3. The antagonistic effects of isolated bacterial strains on the development of pathogens, including Vibrio alginolyticus, Vibrio harveyi, Streptococcus iniae, and Streptococcus agalactiae, were investigated using Luria-Bertani (LB) agar plates. All the isolated bacteria exhibited inhibitory effects against the pathogens, including V. alginolyticus, V. harveyi, S. iniae, and S. agalactiae. These isolated bacteria were characterized with a wide range of antagonistic activities, non-hemolytic activities, high survivability after heat-treatments and safety confidence, and antibiotic susceptibility. Generally, the characteristics displayed by these strains indicated that they could be used as potential probiotics in the aquaculture industry.

Different saturated and monounsaturated fatty acids levels in fish oil-free diets to cobia (Rachycentron canadum) juveniles: Effects in growth performance and lipid metabolism

This study aimed to investigate the influences of alternative lipid sources rich in saturated and monounsaturated fatty acids (SFA and MUFA) supplemented with long-chain polyunsaturated fatty acids (LC-PUFA) on production performance and lipid metabolism of Rachycentron canadum (cobia) juveniles. An 8-week feeding trial was carried out using four isoproteic and isolipidic diets as follows: FO-D (fish oil, as control diet), SFA-D (rich in SFA), MIX-D (same levels of SFA and MUFA), and MUFA-D (rich in MUFA). Experimental diets were supplemented with arachidonic acid (ARA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) (3, 5, and 10 g kg1, respectively). The growth performance, fatty acid (FA) profile of liver and muscle, hepatocyte morphology, and gene expression related to the FA synthesis and oxidation on the liver were examined. In general, production performance was not impaired in fish-fed FO-free diets, supporting the hypothesis that alternative lipid sources could be used in cobia's aquafeed formulations when the LC-PUFA are adequately supplemented. High dietary SFA levels were disproportionally deposited the liver and muscle. Contrariwise MUFA was mainly deposited in the liver and muscle, reflecting the dietary inclusion levels. The main FA influencing this pattern were 12:0 and 18:1n-9. The expression of fatty acid synthase (fas) was up-regulated in the FO-D group compared to SFA-D and MIX-D groups. There were no differences in the relative expressions of carnitine palmitoyltransferase 1 (cpt-1α) and lipase lipoprotein (lpl). The liver morphology results indicated that fish-fed SFA-D presented a smaller lipid vacuoles area than those fed other experimental diets. This study shows that SFA with shorter carbon chains such as 12:0 can be administered in cobia aquafeeds to stimulate these molecules' catabolism, providing energy for growth, and retaining LC-PUFAs in tissues, especially in the muscle, exhibiting a healthier fillet for consumers.

First report on genetic characterization, cell-surface properties and pathogenicity of Lactococcus garvieae, emerging pathogen isolated from cage-cultured cobia (Rachycentron canadum).

The diseased cage-cultured cobia (Rachycentron canadum) displayed clinical signs, haemorrhagic eyes, dorsal darkness and gross pathological lesions, enlargement of spleen and liver. Haemorrhages were found in brain, heart and liver with cumulative mortality rates ranging from 20% to 50%. Extensive congestion in the heart, liver, spleen, kidney and brain was observed histopathologically. Epicarditis and meningitis were also revealed in diseased cobia. All isolates recovered from the organs (liver, spleen, head kidney, posterior kidney, brain and muscle) of cobia were found to be gram-positive, non-motile, ovoid cocci, short-chain-forming (diplococci) and α-haemolytic. The API 32 strep system together with the polymerase chain reaction assay for species-specific primers (pLG1 and pLG2) and the internal transcribed spacer (ITS) region (G1 and L1 primers) confirmed all four selected isolates as Lactococcus garvieae. Partial 16S rDNA nucleotide sequence (~1,100bp) of one representative L.garvieae isolate AOD109191 (GenBank accession number, MW328528.1) shared 99.9% identities with the 16S rDNA nucleotide sequence of L.garvieae (GenBank accession numbers: MT604790.1). Transmission electron microscopy (TEM) evaluation of one representative L.garvieae isolate (AOD109191) and the results of multiplex PCR did not reveal the presence of the capsular gene cluster (CGC), thus categorizing the isolate as the KG+ phenotype. Capsule staining and TEM observations confirmed the presence of a hyaluronic acid-like capsule, a possible virulence factor in KG+ phenotype L.garvieae isolates. The pathogenic potential of the representative isolate (AOD109191) was assessed through intraperitoneal injection challenges in cobia. The gross lesions and histopathological changes found in experimentally infected cobia were similar to those seen in naturally infected fish. This is the first report that confirms L.garvieae-induced 'warm water lactococcsis' can cause outbreaks of diseases in cage-cultured cobia.

Effects of hypoxia-reoxygenation conditions on serum chemistry indicators and gill and liver tissues of cobia (Rachycentron canadum)

Cobia (Rachycentron canadum) is an important cultured marine fish species in southern China. It is characterized by fast growth. Due to the effects of climate change on water oxygen levels and seawater temperatures, the understanding of the influence of environmental changes on cobia culture has become important. In this study, to explore the stress and adaptability of cobia under hypoxia-reoxygenation conditions, the fish were exposed to an oxygen-deficient environment with dissolved oxygen (DO) level of 2.64 ± 0.25 mg/L. Serum liver function target, lipid metabolism-related enzymes and the serum antioxidant capability were detected in cobia under acute hypoxic stress after which fish returned to normal DO level (6.34 ± 0.15 mg/L) at 8, 24 and 48 h. Conventional paraffin sectioning and hematoxylin and eosin (H-E) staining were used to observe gill and liver tissues of cobia by electron microscopy. After hypoxic stress, the activities of alkaline phosphatase (ALP), total protein (TP), albumin (ALB), triglyceride (TG), total cholesterol (TC) and superoxide dismutase (SOD) in cobia decreased. Under acute hypoxic stress, the gill patches of the fish were contracted and slightly curved. Liver disorder and vacuoles appeared between liver tissues. After reoxygenation, SOD and catalase (CAT) were recovered to the level of the control group with time, and all peaks appeared. The gill and liver of fish were also recovered with time. The results showed that hypoxic stress could cause oxidative damage to cobia.

Morphometry in Coronary Arteries of Beijupira (Rachycentron canadum) Fish with Tunics Hyperplasia

Tunics hyperplasia of blood vessels can be quantified by a range of techniques that relate to modifications of area or thickness on histological sections. We studied hyperplasia of tunics of coronary arteries in a fish species, Rachycentron canadum for establishing the relationship between tunics and luminal obstruction by morphometry. The morphometric analysis was performed on 158 arterial vessels of 40 fish samples. The histological slides of cardiac and vascular tissue were stained using hematoxylin and eosin and observed under an optical microscope. The data relating to the proportion of the lumen area compared to the area of the tunic media were analyzed according to Beta regression models. The lumen proportion showed a decreasing relationship with weight and length of the analyzed animals. A linear relationship was not observed between lumen proportion and areas and/or radius of arterial tunics. It is concluded that the increase in weight gain contributes to a reduction of lumen area, leading to arterial obstruction without increasing or decreasing relationship between the proportion of vascular lumen and the thickness of arterial tunics. The set of abnormalities described are likely to be attributed to nutritional factors during the fish cultivation.

Feeding habits and growth characteristics of cobia (Rachycentron canadum) larval and juvenile stages

The feeding habits and growth of larvae and juveniles under artificial culture conditions were examined using the ecological method of simple random sampling to better understand the feeding characteristic of cobia (Rachycentron canadum) during the early development stage. The results showed that cobia larvae had a good foraging capability. After three days of the hatch (DAH), the larvae began feeding, and the feeding incidence was 70%. Feeding incidence was 100% in the case of juveniles. Feed intake of larvae and juveniles increases with increased body mass and could be expressed using the binomial equation (R2 = 0.9188). The digestive tract fullness coefficient of 3–24-day-old larvae and juveniles fluctuated from 0.1% to 1.0%. The larvae and juveniles of cobia were satiated within 1 h. The digestion time of larvae to rotifers and copepods was between 0.5 and 1.5 h and 0.5–2 h, respectively, while that of juveniles was 1–3 h. The daily feeding rates of larvae and juveniles were 61.38% (5-day-old), 54.18% (10-day-old), and 24.85% (24-day-old), and could be used as a reference for the daily feeding (%) of both larval and juvenile stages of cobia. The feeding patterns of larvae and juveniles showed a circadian rhythm, suggesting that they were fed during the day. The average daily growth rate of full-length larvae and juveniles aged 3 to 24 days was 35.90%, with an average daily weight gain rate of 56.97%. The relationship among total length, body mass, and age were expressed using a quadratic equation of one variable (R2 > 0.90) and a power function (R2 > 0.90) for the regression equation of body mass and full length. This study provides useful insights on the early development stage, and a reference for large-scale production of cobia larvae and juveniles.

Identification and characterization of miRNAs and target genes response to hypoosmotic adaption in the cobia, Rachycentron canadum

Environmental salinity is a major factor influencing growth and development, reproduction, and physiology in fish. Recently, miRNAs have been confirmed to play an important role in regulating organismal adaptation in salinity challenge. Since the genomic studies on cobia (Rachycentron canadum) are limited, the miRNA transcriptome of R. canadum is important to investigate the salinity adaptation. In this study, the miRNA transcriptome analysis of the gills in R. canadum was performed under conditions of normal salinity (30‰) and low salinity (10‰). In total, 409 known miRNAs and 139 novel miRNAs were identified, with 56 DEMs (differentially expressed miRNAs). There were 64,983 target genes predicted based on the R. canadum transcriptome, in which 43,283 target genes were attributed to DEMs. The GO annotation and KEGG pathway analysis of target genes indicated that metabolic pathways and signal transduction were the most strongly affected pathways in R. canadum to tackle low-salinity stress, and R. canadum maintains osmotic homoeostasis and energy balance by regulating miRNAs in metabolism, ion channels, and transporters to adapt to low salinity. Overall, this study provides valuable genomic resources to further understanding the fundamental mechanisms of miRNA regulation in marine teleost response to hypoosmotic stress adaption.

Electronic sensory assessment of bread enriched with cobia (Rachycentron canadum)

AbstractThe aim was to evaluate the sensory quality by electronic nose (EN) and tongue (ET) of bread added by cobia minced protein in differents times of storage. Two samples were elaborated: (a) control (FF—traditional bread); (b) added by 10% Cobia minced protein (FPN). The two samples of bread were analyzed from time “zero” (1 hr after being baked) to time “five” (120 hr). A Portable EN (PEN2) composed of 10 sensors was used. Operating conditions: flow rate 300 ml/min, injection time 60 min, flush time 180 min. To ET (Taste‐Sensing System SA402B) 5 sensors were used. All samples were analyzed twice and the average was analyzed by Principal Component Analysis, showing the relationship among the samples and the variables. The greatest differences between the odors were observed after 120 hr of storage. In the first 48 h, the EN was unable to differentiate the samples. The biggest differences of taste were observed at t0. In the other evaluation times, the samples reduced their differences. The use of electronic sensory methods showed promising. Confer greater specificity in the determination of odors and taste of products. Therefore, these tools can be used to improve the sensory characteristics of the new products, as enriched foods.Practical ApplicationsBread is a basic food of the world population, but it does not present a big quantity/quality protein content. Using fish protein concentrate in bread improves the nutritional quality of this product, however, in function of the physico‐chemical composition, fish and derivates may present a strong characteristic odor/taste, rejected by a large part of the population. The sensory characteristics of a product are determining factors for the choice and purchase by the consumers. Maintaining a permanent panel of trained evaluators takes high time and continuous costs, and is not entirely accurate. The use of technologies used by the electronic nose and tongue can assist in a greater standardization of food, especially when it involves the development of new products, ingredients, or differentiated raw ingredients, as made in this study.

Effects of Electronarcosis on Frozen Fillets Quality of Cobia (Rachycentron canadum)

ABSTRACT The objective of this study was to evaluate the influence of three different electronarcosis voltages (50, 100, and 150 V) on the physical and chemical parameters of cobia (Rachycentron canadum) fillets during storage for 180 days (−18°C). After electronarcosis, fish were slaughtered by gill cutting and filleted. Then, the fillets were frozen until analyses (–80°C for 20 min, followed by −18°C for up to 180 days) carried out on samples every 60 days. In general, fillet cooking loss was lower in fish corresponding to day 180, and fillets from fish desensitized with 50 V electronarcosis presented significantly higher cooking loss. In fish corresponding to day 180, drip loss was the lowest in fillets from cobia desensitized with 50 V. The levels of thiobarbituric acid-reactive substances (TBARS) were significantly higher in fish corresponding to day 120. The color parameters increased in fish corresponding to day 180 in fillets from group exposed to 50 and 100 V. Denaturation of actin increased with storage in fillets obtained from fish desensitized with 150 V. In conclusion, cobia fillets can be preserved by freezing for 180 days when electronarcosis is applied at 50 or 100 V as a desensitization method for slaughtering.

Changes in the PI3K/Akt/TOR signalling pathway after methionine treatment in the primary muscle cells of cobia ( rachycentron canadum )

Methionine (Met) plays important roles in protein synthesis and in diverse cellular processes in eukaryotes. In the present study, primary muscle cells of cobia fish Rachycentron canadum were isolated and treated with Met at different concentrations (0.5, 1, 2, 5 or 10 mM) for 24 h in culture media. The results show that the 5 mM Met group had the highest cell viability and total protein content. The phosphorylation levels of phosphoinositide 3-kinase (PI3K) p85 on Tyr458 and of protein kinase B (Akt) on Ser371 were significantly affected by the Met concentration during incubation. Cells incubated with 5 or 10 mM Met showed higher mRNA levels of the target rapamycin (TOR) and higher phosphorylation levels of TOR on Ser2448. Cells incubated with 5 mM Met had the highest phosphorylation levels of ribosomal p70-S6 kinase (S6K1) on Ser371 and of 4E-binding protein 1 (4E-BP1) on Thr37/46. Cells incubated with PI3K and TOR inhibitors showed that LY294002 and rapamycin significantly inhibited the phosphorylation of Akt on Ser371 and of TOR on Ser2448 respectively. These results indicate that Met concentration affects cell viability and is associated with changes in the PI3K/Akt/TOR pathway.

Effects of hypoxia stress on the intestinal microflora of juvenile of cobia (Rachycentron canadum)

Hypoxia is one of the most frequently arising stressors in aquaculture. Hypoxia causes huge financial losses and degradation of resources. However, the response of cobia (Rachycentron canadum) to hypoxia stress is not completely understood. In this study, the effects of hypoxia on the intestinal microflora of juvenile cobia were investigated. The diversity and structure of microflora after 4 weeks of hypoxia stress were analyzed using high-throughput sequencing technology. A total of 210 fish were divided into two treatment groups, namely, hypoxic stress and normoxic control groups, with 3 replicates per group and 35 fish per replicate. The results showed that the richness and diversity of intestinal microflora increased significantly first and subsequently decreased significantly after invitation of the hypoxia stress (P < 0.05). Principal coordinate analysis (PCoA) showed that hypoxia changed the structure of the intestinal microflora. At the phylum level, Proteobacteria, Firmicutes, Spirochaetes, Tenericutes, and Bacteroidetes were the dominant bacteria. Compared to the control groups, the relative abundance of Proteobacteria increased significantly (P < 0.05) in H7, H14, and H28 groups, which was opposite to that of Tenericutes. The abundances of Firmicutes and Tenericutes both increased significantly (P < 0.05) in the H14 group. At the genus level, the relative abundance of Photobacterium increased significantly (P < 0.05) in the H7, H14, and H28 groups, while that of Brevinema decreased significantly (P < 0.05) in the H1 and H7 groups. Mycoplasma decreased significantly (P < 0.05) at all the time points of hypoxia, while Methylobacterium decreased significantly (P < 0.05) in the H7 and H28 groups. In addition, linear discriminant analysis (LDA) effect size (LefSe) analysis results indicated that hypoxia caused a significant increase in the relative abundance of Actinomyces, Pseudoalteromonas, Staphylococcus, γ-Proteobacteria, Vibrionaceae, and Pseudomonadales, which were the biomarkers of the hypoxia group. These results provide an understanding of the effects of hypoxia stress on the intestinal microflora of juvenile cobia.

Regional-scale variability in the movement ecology of marine fishes revealed by an integrative acoustic tracking network

Marine fish movement plays a critical role in ecosystem functioning and is increasingly studied with acoustic telemetry. Traditionally, this research has focused on single species and small spatial scales. However, integrated tracking networks, such as the Integrated Tracking of Aquatic Animals in the Gulf of Mexico (iTAG) network, are building the capacity to monitor multiple species over larger spatial scales. We conducted a synthesis of passive acoustic monitoring data for 29 species (889 transmitters), ranging from large top predators to small consumers, monitored along the west coast of Florida, USA, over 3 yr (2016-2018). Space use was highly variable, with some groups using all monitored areas and others using only the area where they were tagged. The most extensive space use was found for Atlantic tarpon Megalops atlanticus and bull sharks Carcharhinus leucas. Individual detection patterns clustered into 4 groups, ranging from occasionally detected long-distance movers to frequently detected juvenile or adult residents. Synchronized, alongshore, long-distance movements were found for Atlantic tarpon, cobia Rachycentron canadum, and several elasmobranch species. These movements were predominantly northbound in spring and southbound in fall. Detections of top predators were highest in summer, except for nearshore Tampa Bay where the most detections occurred in fall, coinciding with large red drum Sciaenops ocellatus spawning aggregations. We discuss the future of collaborative telemetry research, including current limitations and potential solutions to maximize its impact for understanding movement ecology, conducting ecosystem monitoring, and supporting fisheries management.

First report of intersex in Cobia, Rachycentron canadum reared in Gulf of Mannar, India—A case study

The present study reports the first incidence of intersex in Cobia, Rachycentron canadum maintained at sea cages in the Gulf of Mannar, India. During the 10 year study period (2010–2019), at total of 815 broodstock (386 wild captured and 429 captive raised) were maintained under captivity in sea cages in the Gulf of Mannar, India for the purpose of seed production. Of which, 318 male and 252 female broods’ gonads were examined post-mortem following a natural death. Only one male fish was found with a visible gonadal anomaly. Microscopic analysis of gonad revealed the presence of both the characteristic female and male tissues in testes of a single specimen (testis-ova). Only the abnormal nodular portion contained primary oocytes, whereas the central testicular tissue contained spermatocytes and spermatids in the seminiferous lobules. This is the first reported intersex of cobia from the Gulf of Mannar, India. It could be interpreted as low-level rare incidence of natural aberration.

Records of new and rare alien fish in North African waters: the burrowing goby Trypauchen vagina (Bloch and Schneider, 1801) and the bartail flathead Platycephalus indicus (Linnaeus, 1758) in Egypt and the cobia Rachycentron canadum (Linnaeus, 1766) in Libya

Records of new and rare alien fish in North African waters: the burrowing goby Trypauchen vagina (Bloch and Schneider, 1801) and the bartail flathead Platycephalus indicus (Linnaeus, 1758) in Egypt and the cobia Rachycentron canadum (Linnaeus, 1766) in Libya

A new cobia (Teleostei, Rachycentridae) species from the Miocene St. Marys Formation along Calvert Cliffs, Maryland, USA

AbstractThe highly fossiliferous St. Marys Formation is exposed along Calvert Cliffs, Maryland, and comprises one of the best available records of late Miocene life in the northeastern United States. Rachycentron stremphaencus new species, a cobia from the late Miocene (Tortonian) of the St. Marys Formation is described herein on the basis of a single three-dimensional neurocranium. This fossil represents the earliest known occurrence of neurocranial remains of the genus Rachycentron in the record. Rachycentron stremphaencus differs from Rachycentron canadum (Linnaeus, 1766) in many ways. The most obvious include a different ornamentation of the outer surface of the cranial bones; a notably pronounced lateral ridge resulting in a considerable gradient from the dorsal-medial exposure of the frontal to its lateralmost supraorbital margin; the size, shape, and position of the sphenotic that is located in the posterior half of the neurocranium and its lateralmost edge being adjacent to the anteriormost extent of the wedge-shaped trough in the dorsal surface of the skull formed by the lateral and medial ridges; the two contralateral medial ridges forming a proportionately much wider trough on either side of the supraoccipital; the epioccipitals not reaching the rear edge of the neurocranium; and the lack of a conspicuous posterolateral prong of the intercalar.UUID: http://zoobank.org/c8523bb4-2de2-4318-9a37-027f463a0441

Analysis of the chemical properties of salted cobia (Rachycentron canadum)

Abstract Aquaculture of cobia (Rachycentron canadum) is still incipient in Brazil, as well as the sale of its meat. However, there is a market demand for this product in the state of Rio de Janeiro. The salting process for the meat of cultivated cobia is a way of preserving and marketing the product for the growers. Thus, the present study aimed to assess the chemical properties of salted cobia meat. Market-sized cobia grown in net-tanks located in Baia de Ilha Grande, Angra dos Reis, Rio de Janeiro, Brazil were used. The fish were eviscerated (gutted), beheaded and lightly flattened. The fillets “charutos” were then subjected to brine salting for 6 days, immersed in saturated brine at refrigeration temperature. After the preparation of the product, analyzes of percent composition, chloride content and lipid profile were performed. The product had high concentrations of protein (20.16%), lipids (19.88%) and 6.56% of total chloride. Lipid profile assessment showed significant percentages of palmitic (6.66%) and oleic (4.99%) acids. Therefore, it is concluded that the salted meat of cobia has good nutritional quality, and the product is a source of palmitic and oleic acids that help preventing cardiovascular diseases and lowering cholesterol levels.

Extractability and physicochemical properties of cobia ( Rachycentron canadum ) skin collagen as influenced by lactic acid concentration

The present research aims to elucidate the effect of lactic acid concentration on the extractability and physicochemical properties of cobia (Rachycentron canadum) skin collagen. The cobia skin acid-soluble collagen (ASC) was isolated using different concentrations of lactic acid (0.5 M and 1.0 M) and characterized on its extractability and physicochemical properties. The extract using 0.5 M lactic acid gives a higher yield compared to using 1.0 M lactic acid. The moisture, protein, fat, and ash content of cobia skin ASC extracted using 0.5 M was higher than extracted using1.0 M lactic acid. The functional group present in both extracts was amide A, amide I, and amide III. Both extracts at different lactic acid concentrations showed decreasing on relative viscosity with temperature increased. Thus, different extractability and physicochemical properties of cobia skin ASC extracts exhibits based on the lactic acid concentration and it would produce collagen with multi potential application. Practical applications The best way to minimize the environmental contaminations from fish processing industrial waste and provide the economic value to waste materials is collagen production. Collagen prepared from fish skin can utilize in various purposes as biopolymer. Extraction of collagen from a chemical method by utilizing organic acid like acetic acid, chloroacetic acid, citric acid, lactic acid, or inorganic acid like hydrochloric acid is more suitable due to low-cost effective which compared to enzyme like pepsin. The present study focused on the utilization of lactic acid at different concentration produces collagen with multipotential application with extractability and physicochemical properties.

Biochemical composition and activities of digestive and antioxidant enzymes during the egg and yolk‐sac larval development of the cobia ( Rachycentron canadum )

Cobia Rachycentron canadum is an economically important fish and is cultured throughout southern China and other part of the world. However, the knowledge of metabolism and nutritional requirements of cobia embryos remains limited. This study investigated changes of the biochemical composition, as well as the activities of related digestive and antioxidant enzymes during the development of both eggs and yolk-sac larvae of the cobia (Rachycentron canadum). The results showed that egg mass at the fertilized stage increased gradually to the blastula stage and showed a significant increase at the segmentation stage and a significant decrease at the larval period. The main components of embryos and larvae were carbohydrates, lipids and proteins. Protein and lipid contents decreased at the blastula stage, increased significantly at the segmentation stage and then decreased thereafter. Carbohydrate contents decreased significantly during the development. Enzymatic activities showed a progressive increase from the embryo to the yolk-sac larval stage. The activities of pepsin and trypsin increased significantly during the development. Amylase activity remained low before the blastula stage and increased rapidly thereafter. Lipase showed an ‘increase–stable–increase’ tendency. Changes of digestive enzyme activities indicated the dynamics of the biochemical composition. Activities of glutathione peroxidase, catalase and superoxide dismutase significantly increased during embryonic and yolk-sac stages, and malondialdehyde contents followed the same trend. The results of the current research provide vital information to enhance yolk exploitation with a specific focus on organogenesis. Moreover, considerable knowledge on the embryonic development of the cobia is presented.

A scalable, satellite-transmitted data product for monitoring high-activity events in mobile aquatic animals

A growing number of studies are using accelerometers to examine activity level patterns in aquatic animals. However, given the amount of data generated from accelerometers, most of these studies use loggers that archive acceleration data, thus requiring physical recovery of the loggers or acoustic transmission from within a receiver array to obtain the data. These limitations have restricted the duration of tracking (ranging from hours to days) and/or type of species studied (e.g., relatively sessile species or those returning to predictable areas). To address these logistical challenges, we present and test a satellite-transmitted metric for the remote monitoring of changes in activity, measured via a pop-off satellite archival tag (PSAT) with an integrated accelerometer. Along with depth, temperature, and irradiance for geolocation, the PSAT transmits activity data as a time-series (ATS) with a user-programmable resolution. ATS is a count of high-activity events, relative to overall activity/mobility during a summary period. An algorithm is used to identify the high-activity events from accelerometer data and reports the data as a count per time-series interval. Summary statistics describing the data used to identify high-activity events accompany the activity time-series. In this study, we first tested the ATS activity metric through simulating PSAT output from accelerometer data logger archives, comparing ATS to vectorial dynamic body acceleration. Next, we deployed PSATs with ATS under captive conditions with cobia (Rachycentron canadum). Lastly, we deployed seven pop-off satellite archival tags (PSATs) able to collect and transmit ATS in the wild on adult sandbar sharks (Carcharhinus plumbeus). In the captive trials, we identified both resting and non-resting behavior for species and used logistic regression to compare ATS values with observed activity levels. In captive cobia, ATS was a significant predictor of observed activity levels. For 30-day wild deployments on sandbar sharks, satellites received 57.4–73.2% of the transmitted activity data. Of these ATS datapoints, between 21.9 and 41.2% of records had a concurrent set of temperature, depth, and light measurements. These results suggest that ATS is a practical metric for remotely monitoring and transmitting relative high-activity data in large-bodied aquatic species with variable activity levels, under changing environmental conditions, and across broad spatiotemporal scales.