Cobia Aquaculture Research Articles

Opportunities and challenges for cobia, Rachycentron canadum aquaculture in the United Arab Emirates

Among the many candidate local species identified for development of aquaculture in the United Arab Emirates (UAE), cobia (Rachycentron canadum) has the great potential for farming in floating cage systems. Successful spawning and rearing of larvae and juveniles was first achieved by the Aquaculture and Marine studies Center, Abu Al Abyad Island, Abu Dhabi in 2008. The first trial to grow cobia in near shore cages of 55 m³was done in 2009 when the stocked fish reached an average weight of 2.87 kg in 12 months rearing period. Subsequently two more attempts were carried out in larger 15 meter diameter (636 m³) cages in 2022, the results of which were not encouraging. There are many challenges for the development of cobia farming in UAE. This article highlights the current technological challenges, sustainability issues, marketing strategies and policy matters that confront the development of commercial cobia aquaculture in the UAE and offers some recommendations.

Effect of dietary carbohydrate level on growth, feed utilization, energy retention, body composition, and digestive and metabolic enzyme activities of juvenile cobia, Rachycentron canadum

Carnivorous fish, such as cobia Rachycentron canadum, tend not to have a specific requirement for dietary carbohydrates (CBH). However, if CBH is not provided in the diet, other energy-yielding nutrients, such as protein and lipids, are catabolized to produce energy. Therefore, knowing the optimum level of dietary CBH would be useful for cobia aquaculture. In the present study, four isonitrogenous and isolipidic diets were prepared to investigate the effects of dietary CBH level (4.8–22.5 %) on growth performance and body composition of, and feed utilization, by juvenile cobia (initially weighing 22.2 ± 0.27 g/fish). Each diet was given to triplicate groups of cobia for 8 weeks. Both the final body weight and specific growth rate increased with increasing dietary CBH levels. Feed intake decreased with increasing dietary CBH levels (P < 0.05), whereas, feed efficiency and the protein efficiency ratio increased (P < 0.05). As the level of dietary CBH increased, the condition factor, hepatosomatic index, viscerosomatic index, and intraperitoneal fat ratio generally increased (P < 0.05). The whole-body lipid content generally increased with increasing dietary CBH levels, with the lipid content of fish fed a 22.5 % dietary CBH diet being significantly higher than other treatments. Moisture content showed the reverse response to that of lipids. Body protein and ash contents were not significantly related to dietary CBH (P > 0.05). Activities of hepatic glucokinase increased with increasing dietary CBH levels, being significantly higher in fish fed a 22.5 % CBH diet compared with other groups (P < 0.05). In contrast, the activities of hepatic hexokinase and pyruvate kinase showed the opposite trend. The activities of intestinal amylase and trypsin were negatively related to dietary CBH levels. Thus, dietary CBH promoted the growth and feed utilization of cobia, although it also had negative effects, such as higher lipid deposition and higher body indices. Based on these results, we recommend that inclusion of CBH in the diet of cobia is beneficial, whereas, the optimal level of CBH should be carefully evaluated.

Influences of indigenous isolates Pantoea agglomerans RCS2 on growth, proximate analysis, haematological parameters, digestive enzyme activities, serum biochemical parameters, antioxidants activities, intestinal morphology, disease resistance, and molecular immune response in juvenile's cobia fish (Rachycentron canadum)

The fast expansion and high intensity of cobia culture or, better still, farming has resulted in diseases infestation and has been recognised as a significant evolving problem for cobia culture throughout its production cycle. This study explored the possible effects of dietary additives of indigenous Pantoea agglomerans RCS2 on growth, haematological parameters, biochemical blood indices, antioxidant enzyme activities, disease resistance, digestive enzyme activities, and molecular immune response in juvenile's cobia fish. After 70 days, the growth parameters (i.e., specific growth rate, weight gain, and final weight) and feed conversion ratio significantly improved (P < 0.05) compared to those fed diets without supplementation. Also, haematological parameters such as red blood cells, white blood cells, corpuscular haemoglobin concentration, mean corpuscular volume, haemoglobin, and Mean corpuscular haemoglobin were high significantly (P < 0.05) in supplemented groups. The serum blood biochemical indices aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, triglyceride, cholesterol, and glucose recorded no significant difference (P > 0.05) while globulin, total protein, and albumin were high significantly (P < 0.05) in supplemented groups as compared to the group without supplement. The current results displayed that the activities of superoxide dismutase, glutathione peroxidase, and catalase in the liver and head kidney were affected by dietary supplements of indigenous isolated microorganisms. An exceptionally low mortality rate was observed in the treatment groups than the group without supplemented diets when challenged with pathogenic bacteria. Similarly, light microscopy revealed an increase in the intestinal villus length in fish fed with the supplemented diet compared to those without supplements. In this study, the higher digestive enzyme activities show that supplemented bacteria isolates have impacted digestive enzyme secretion in juvenile cobia. Regarding the gene expression, Interleukin-1 Beta (IL-1β), Tumour necrosis factor α (TNFα), and Interleukin-8 (IL-8) were all up-regulated by indigenous isolates. The current results show that the dietary additive of indigenous P. agglomerans RCS2 could constitute a treasured nutritional approach in the path of a sustainable cobia aquaculture. The fish immune responses enhancement and the gut morphology are vital in enhancing growth, absorption of nutrients, and disease resistance; hence the results in the present study are essential outcomes for the development and competitive aquaculture sector.

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.

Evaluating a Suitable Aquaculture Site Selection Model for Cobia (Rachycentron canadum) during Extreme Events in the Inner Bay of the Penghu Islands, Taiwan

Despite numerous studies on the effect of a cold weather disaster on fisheries in 2008, no operational systems have been developed to monitor the threat of such an event to mariculturists in the Penghu Islands (PHI) region of Taiwan. The present study employed a suitable aquaculture site selection map of the inner bay of the PHI to reduce aquaculture losses and mortality rates of cobia (Rachycentron canadum) during extreme events. Daily marine environmental data, including sea surface temperature (SST), chlorophyll-a concentration (chl-a), and wind speed in the winter, were collected. An extreme event was defined as a period of over 11 days in a month of strong winds (&gt;6 m/s). Four parameters in the PHI inner bay, including SST, cold-water intrusion days, chl-a, and offshore distance to the PHI coastline, were used to evaluate suitable aquaculture sites for cobia culture. The results indicated that La Niña events could not be used as a factor to detect cold-water intrusion events and select suitable aquaculture sites in the PHI. The evaluated suitable aquaculture site selection map, obtained using an arithmetic mean model and a geometric mean model, revealed that the avoidance sites during extreme events were concentrated in the northern and northwestern PHI. Suitable areas were concentrated in the southeastern areas. We further suggested that commercial cobia aquaculture operations in the PHI inner bay could be moved to the suitable sites in southeastern PHI during extreme events.

Sediment Characteristics under and Around Cobia Cage Farms at Penghu, Taiwan, As Visualized By Redox Potential and Sulfide Content Profiles Using GIS as Documentation Tool

Redox potential is a frequently used measurement in studies under and around marine cage farms to assess the environmental status of marine aquaculture. This study presents an application of a geographic information system (GIS) to document sediment geochemical measures in cobia aquaculture in order to assess the condition of the benthic environment using the Chu-Wan marine fish farm as a case study. The objectives of the study was to combine GIS presentation with chemical measures as an important and innovative methodology in marine aquaculture environmental management. The results show a real distribution patterns for both redox potential and sulfide content in relation to position of the farm and the current pattern.

Analysis of sexually dimorphic growth in captive reared cobia (Rachycentron canadum) and the occurrence of intersex individuals

The growth of three cohorts of captive reared cobia, grown in a combination of flow-though and recirculating aquaculture systems, was progressively measured to determine the existence and extent of sexually dimorphic growth in cobia. Approximately 100 fish from each cohort were individually identified and regularly weighed until the average weight of the fish was approximately 5kg. The sex of individuals was determined through gonadal observations at the conclusion of each trial and the gender fitted retrospectively to the growth data set. Intersex gonads were observed in the first two cohorts of cobia, with 16.9% incidence in cohort 1 and 6.8% in cohort 2. Cobia is considered a gonochoristic species. This was the first reported observation of intersex gonads in cobia and the first reported occurrence of intersex gonads from a gonochoristic fish species from Australian waters. Only one fish out of the 182 examined in the third cohort was identified as intersex. There was no sexually dimorphic growth in cobia when there was a relatively high incidence of the intersex anomaly, as seen in the first two cohorts of fish. In the relative absence of the intersex condition, female cobia was significantly larger than males from 2kg onwards. The weight of female cobia was almost 30% more than that of males at 17months of age when average weight of the cohort was 4.6kg. It is likely that the first two cobia cohorts were exposed to endocrine disruption in some form, and the possible sources are discussed.Statement of relevanceThis study demonstrated that female cobia grow significantly faster than male fish and that investigations into monosex culture could lead to significant productivity gains for cobia aquaculture. It also demonstrated that cohorts containing intersex fish did not exhibit sexually dimorphic growth. It is likely that the reproductive anomaly is the result of disruption to the endocrine system.

Replacement of fish meal by a novel non-GM variety of soybean meal in cobia, Rachycentron canadum: Ingredient nutrient digestibility and growth performance

A constraint for the expansion of cobia aquaculture is the availability of high quality formulated diets which reduce or eliminate fish meal (FM) protein. Therefore, the nutritive value of a novel soybean cultivar, Navita™ (Navita, non-genetically modified and selectively bred soy), and regular, commodity soybean meal (SBM, de-hulled, defatted, roasted and solvent-extracted) was evaluated for cobia, Rachycentron canadum via separate digestibility and growth trials. In the first experiment Navita's apparent digestibility coefficients (ADC) were higher than those of SBM for nearly every nutrient evaluated. Crude protein ADCs were 82 and 69% for Navita and SBM, respectively. Apparent DC for amino acids ranged from 68 to 109% for Navita whereas, amino acid ADCs for SBM varied from 42 to 98%. The feeding trial utilized fish of a size that more closely resembles commercial cobia stocking (1.8kg), and was conducted over a 91-day period. Experimental diets (iso-nitrogenous and iso-energetic) were formulated such that 67% of the FM protein in the reference diet was replaced by either a combination of SBM+soy protein concentrate (SPC, Solae Profine®) labeled MXSB-diet, or by a combination of SPC+Navita; Navita-diet, hereafter. A fourth experimental diet had 80% of the FM protein replaced by a combination of Navita+SPC and was identified as Navita-high. No significant differences (P>0.05) were observed in fish fed the experimental diets for feed conversion ratio, protein efficiency ratio, feed efficiency, mean daily intake, gross protein intake, gross energy intake, visceral somatic index, muscle ratio, and hepatosomatic index. Fish fed the Navita-high diet had the lowest fish in:fish out ratio (FIFO) at 0.9±0.16. These results indicate that Navita meal can be incorporated at very high levels in the diet of marine carnivorous fish such as cobia with no detriment to performance, making it a prime candidate for FM replacement in aquafeeds.

Diet supplementation of Pediococcus pentosaceus in cobia (Rachycentron canadum) enhances growth rate, respiratory burst and resistance against photobacteriosis

Cobia (Rachycentron canadum) is an economically important fish species for aquaculture in tropical and sub-tropical areas. Cobia aquaculture industry has severely damaged due to photobacteriosis caused by Photobacterium damselae subsp. piscicida (Pdp), especially in Taiwan. Antibiotics and vaccines have been applied to control Pdp infection, but the efficacy has been inconsistent. One species of lactic acid bacteria, Pediococcus pentosaceus strain 4012 (LAB 4012), was isolated from the intestine of adult cobia, and its culture supernatant can effectively inhibit Pdp growth in vitro. The acidic pH derived from metabolic acids in LAB culture supernatant was demonstrated to be an important factor for the suppression. After a 2-week feeding of LAB 4012, the growth rate of the fed cobia was 12% higher than that of the non-fed group, and the relative percentage of survival (RPS) of the fed cobia was found to be 74.4 in Pdp immersion challenge. In addition, the respiratory burst (RB) of peripheral blood leukocytes (PBL) in the LAB 4012-fed group was significantly higher than that of the non-fed group. Although feeding LAB 4012 did not improve specific antibody response in cobia after immunization with Pdp vaccine, it still significantly raised the survival rate by 22% over that of the non-fed group after Pdp immersion challenge. Judging by the quick induction of high protection against Pdp infection and promotion of growth in larvae, LAB 4012 was considered to be a viable probiotic for cobia aquaculture.

Dietary taurine enhances growth and digestive enzyme activities in larval cobia

The establishment of a commercial cobia aquaculture is hampered by high mortality rates (>90%) during the larval rearing. Dietary taurine supplementation has been reported to greatly improve survival rates; however, nutritional role of taurine remains poorly understood in fish. The purpose of this trial was to study the effect of taurine supplementation on growth, amylase, lipase, trypsin, and pepsin-like activities during larval cobia development and weaning. Taurine was delivered using bioencapsulation techniques wherein rotifer and Artemia nauplii were co-enriched with 4gtaurineL−1d−1. At first feeding (3 dph), amylase and trypsin activities were detectable while lipase and pepsin-like activities were not. On a per-larvae basis and regardless of taurine supplementation, enzymatic onset commenced around 16 dph, except for pepsin. However, taurine-supplemented larvae had higher specific trypsin and amylase activities prior to 16 dph. Lipase specific activity was significantly increased only at 11 and 22 dph. Pepsin-like activity remained undetectable until 22 dph, at which point the specific activity was higher (P<0.05) in taurine-supplemented larvae. Overall, specific enzyme activities of control larvae were low during the first half of the larval period (3–16 dph) but increased during the second half (17–27 dph). Specific activities of taurine-supplemented larvae showed the opposite trend. Together with previous work, the present data strongly indicate that taurine is an essential nutrient for cobia larvae. Taurine supplementation does not affect the onset of total enzyme activities, but does increase specific amylase and trypsin activities in early larval stages. These heightened enzymatic activities may lead to enhanced nutrient availability, thus providing some explanation to the improved development, growth, and survival rates observed in taurine-supplemented larvae.

Chitinase and apparent digestibility of chitin in the digestive tract of juvenile cobia, Rachycentron canadum

A study was designed to determine the presence of chitinolytic enzymes in cobia. Additionally, the source of the chitinolytic enzymes (bacterial or endogenous) and apparent digestibility of chitinous waste meals were investigated to determine the viability of crustacean processing waste products in juvenile cobia diets. Antibiotics were used to eliminate potential chitinolytic gut flora and chitinolytic enzyme levels were compared to control fish fed an identical diet without antibiotic. Chitinase and chitobiase were measured in the stomach, pyloric caeca, and anterior intestine but were only detected in the stomach. Control stomach chitinase and chitobiase activities were 3075 ± 709 (mean ± SD) and 2076 ± 208 μg N-acetylglucosamine (NAG) g − 1 h − 1, respectively, and not significantly different from antibiotic treatments. This suggests substantial endogenous production and that the activity, if any, from chitinolytic bacteria is not significant. Additionally, high chitobiase levels indicate breakdown of chitin to potentially nutritive NAG. To determine the apparent digestibility coefficient (ADC) of shrimp processing waste meal (shrimp meal) and crab processing waste meal (crab meal) in vivo, diets containing a 70:30 mixture of a reference diet and test ingredient with the inclusion of the non-digestible marker yttrium oxide were fed. Chitin ADC for both crab (mean = 66.8 ± 4.5% SD) and shrimp (78.2 ± 8.0%) meal was high and not significantly different. Organic matter digestion was significantly higher in crab meal than either shrimp meal or the reference diet. However, crude protein, lipid, and gross energy digestion for crab and shrimp meal were not significantly different from the reference diet. Both enzymatic and in vivo results indicate the capability for juvenile cobia to digest chitin through strong endogenous chitinolytic enzymes. The addition of crustacean processing wastes in cobia diets has the potential to reduce the cost of feed production and increase the sustainability of cobia aquaculture by reducing inclusion rates of fish meal and other more expensive ingredients.

Geographic information system applied to measuring benthic environmental impact with chemical measures on mariculture at Penghu Islet in Taiwan

Cobia, Rachycentron canadum, is currently grown by marine aquaculture in Taiwan, particularly on Penghu Islet. Although the effect of marine aquaculture on the environment has been the subject of many studies, an understanding of its environmental impact has yet to be attained, and the continuing expansion of cage farming has caused noticeable ecological declines. Nevertheless, useful tools to measure this environmental degradation are scant. The results of this study suggest that the combination of a geographic information system (GIS) with redox potential and sulfide measurements can be used to definitively assess the condition of the benthic environment near cobia aquaculture sites and to help develop environmental monitoring programs. These applications could easily be adopted to assess multiple marine environmental conditions.

Intensive larval husbandry and fingerling production of cobia Rachycentron canadum

Methods and results of two larval rearing trials of cobia ( Rachycentron canadum) are presented. These trials were designed to test the efficacy of protocols developed over several years of research in cobia larviculture at the UMEH. The protocols incorporate the use of probiotics and prophylaxis, minimize microalgae use, and include commercially available ingredients for live feed enrichment. During the trials, fertilized eggs were stocked at 400/L and incubated in 1000-L cylinder-conical tanks with flow-through seawater at 500% daily exchange rate. Moderate aeration and pure oxygen were used to maintain dissolved oxygen concentrations above saturation (6.5 mg/L at 26 °C). Hatching occurred at 22–24 h post fertilization. Two day-post-hatch (dph) yolk-sac larvae were stocked in four 12,000-L cylinder-conical tanks at 5 and 10 larvae/L. Beginning on 3 dph, larvae were fed microalgae ( Isochyrsis galbana C-strain) at low concentrations (5–10,000 cell/ml) and enriched rotifers ( Brachionus plicatilis) at 3–5/mL through 9 dph. Beginning on 7 dph, enriched Artemia ( Artemia franciscana GSL Strain) nauplii were fed to larvae at 0.1–1/mL. Cobia larvae were reared at water temperatures ranging from 24.3 to 31.8 °C. Water quality parameters were within normal ranges for seawater: salinity 26–34 ppt, pH 7.92–8.16, and NH 3 < 0.18 mg/L. Vigorous aeration and supplemental oxygen were used at all times during both larval rearing trials to maintain adequate water movement and levels of dissolved oxygen (DO) (7.0–9.0 mg/L). Water was filtered down to 10 μm using standard sand filters filled with broken glass media and bag filters prior to entering the tanks. Daily water exchange rates in the tanks ranged from 100% at 3 dph to 500% from 17 dph onwards. Between 20 and 22 dph, all post-larvae were fully weaned onto dry starting diets. Survival rates of post-larvae measuring 1.5–2.0 cm SL and weighing 0.5 g at 20–22 dph were estimated to be ≥ 50%. Further mortality during the nursery stage to 3–5 cm and 1–3 g fingerlings prior to shipping at 27 dph brought the overall survival rate to an average of 25.7%. Survival rates of fingerlings cultured in tanks initially stocked at lower densities (5 larvae/L) was significantly higher ( P = 0.0078). From 15 dph, post-larvae and fingerlings were daily graded by size with large individuals singled out and stocked into another tank. These trials generated 125,328 fingerlings in four tanks in just two months, levels of production that could sustain a commercial operation and indicate that cobia aquaculture can be viable in the Americas.

Culture of cobia ( Rachycentron canadum): cryopreservation of sperm and induced spawning

Studies toward the development of cobia ( Rachycentron canadum) aquaculture were initiated. Methods of cryopreserving cobia sperm were compared and sperm motility was assessed after longterm frozen storage. Sperm stored in 10% dimethyl sulfoxide, 3 mM glucose, and 10% raw chicken egg yolk showed approximately 100% motility upon thawing after more than 1 year of storage at −80°C. Sperm motility declined after about 60 min at room temperature, but approximately 100% motility could be restored by addition of a few drops of 5 mM theophylline. Ripe, wild-caught female cobia were held in recirculating seawater systems and ovulation was induced by injection of human chorionic gonadotropin at a concentration of 275 IU/kg of body weight. Fertilization was attempted using the cryopreserved sperm. Although fertilization did not occur, we are optimistic that cobia aquaculture is feasible.