Larviculture of the Mahimahi Coryphaena hippurus in Hawaii, USA

The Mahimahi Coryphaena hippurus has excellent potential for aquaculture due to its fast growth, good food conversion ratio, high fecundity with natural captive spawns, and high price. Using current technology, three crops a year could yield 288,000 kg/ha of water/yr with a potential profit of US $1,280,000/ha water/yr.
Hatchery methods are now adequate for pilot-scale production, and two venture capital companies are pursuing this course. Significant improvement could be made in egg quality, plankton nutrition, plankton substitutes, disease control, reduced aggression, and weaning feeds. More research is needed to learn about digestive physiology, weaning behavior, and the effects of crowding on mahimahi health. Hatchery production is limited most often by the amount of grown out Artemia or yolk-sac mahi larvae provided for postlarval feeding. Problems that occur at the broodstock, hatching, first feeding, second feeding, third feeding, weaning, and early juvenile stages are discussed.
Using the current technology, the cost of post-hatchery mahimahi is 33 cents per fry. This cost could be reduced to 6 cents per fry by successfully (consistently) weaning postlarvae from live feeds by 25 days.     

Bizarre organism from the skin of mahi mahi, Coryphaena hippurus L. (Teleostei: Coryphaenidae)

Abstract. Superficial stellate cells of an unknown origin were detected on the epidermis of juvenile mahi mahi, Coryphaena hippurus L., up to 60 days of age. The cells occurred in large numbers, and were detected in both wild and cultured fish. International authorities were unable to identify the organism and there was no pathology associated with the presence of the cells on the skin. Because of the fine cytoplasmic interdigitations between the organism and the host cell, and the close ecological association with both wild and cultured juveniles examined, it was thought that the cells could possibly be highly modified skin cells. We report here that the spinous cells possess DNA sequences encoding 16S subunit ribosomal RNA genes distinct from those of mahi mahi, and also that restriction enzyme digests of genomic DNA from the spinous cells and from mahi mahi produced distinct patterns after electrophoretic separation. This suggests that the spinous cells are a bizarre commensal organism displaying a close physical and ecological association with the fish host.     

Enzymes Present in Pancreatic Extracts of the Dolphin Coryphaena hippurus

Pancreatic extract of adult dolphin Coryphaena hippurus was found to have a broad range of proteolytic activity with two peaks, one at pH 5–6 and another at pH 10, when casein was used as a substrate. Enzymes similar in activity to those of pepsin, trypsin, amylase, lipase and collagenase were detected in the extracts by the use of specific chromogenic substrates for each enzyme. The relationship between these enzyme activities, and the formulation of diets for culture of this species, is discussed.     

Reproductive biology of the dolphin fish Corphaena hippurus on the east coast of Taiwan

ABSTRACT: The dolphin fish, Corphaena hippurus Linnaeus, is one of the most important migratory fishes on the east coast of Taiwan. Present results are based on an investigation of 1439 specimens caught using long-line and driftnet, and set net collected monthly between September 1996 and September 1997. The sex ratio of female to male and female combined was 65%, demonstrating a female predominance. Oocytes became mature and transparent when they attained 1.0 mm in diameter. The total number of oocytes per ovary was estimated to range from 2.78 × 10⁵ to 23.48 × 10>⁵, but batch fecundity was noticeably lower than the total number of ovarian eggs, ranging 5.3–32.7% (average 30.1%), and the relative fecundity ranging 10–344/g bodyweight (mean 111/g bodyweight). Minimum body size at sexual maturity was estimated to be 51 cm for both sexes. Dolphin fish spawned throughout the year with reproductive activity peaking in February to March. It is suggested that the dolphin fish has an extended spawning season, during which it lays eggs almost continuously.     

Age, growth, and reproductive characteristics of dolphinfish Coryphaena hippurus in the waters off west Kyushu, northern East China Sea

The growth and reproductive characteristics of dolphinfish Coryphaena hippurus collected in the waters off western Kyushu from May 2008 to April 2011 were determined based on scale and otolith readings and gonad histological examinations, respectively. Based on annual increments in scales and daily increments in sagittal otoliths, the von Bertalanffy growth curves in male and females were determined as $ FL_{t} = 1049[1 - \exp \{ - 0.835(t + 6.975 \times 10^{ - 14} )\} ] $ and $ FL_{t} = 938[1 - \exp \{ - 1.029(t + 6.975 \times 10^{ - 14} )\} ] $ , respectively, where FL _t is the mean fork length (mm) at age t. The spawning period was found to last from June to August for dolphinfish, based on an examination of the monthly changes in the gonadosomatic index and histological observations. Therefore, based on the relationship between the fork length and the developmental stage of the testes or ovaries, male and female dolphinfish were found to reach sexual maturity by the following spawning season after hatching in the northern East China Sea.     

Evaluation of Live Feeds for Larval and Postlarval Mahimahi Coryphaena hippurus

Live hatchery feeds were assayed for fatty acids (FA), amino acids (AA), and their ability to support growth and survival of larval and postlarval mahimahi Coryphaena hippurus at two different hatchery stages. Euterpina acuritrons copepods (C), mahimahi yolk-sac larvae (YSL), Artemia parthenogenica brine shrimp nauplii (BSn), A. parthenogenica juveniles (BSj), and Brachionus plicatilis rotifers (R) were assayed, using several enrichment media. There was little difference in AAs among feeds.
Levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were about 10 times higher in YSL than in their feeds. This explains previous findings where first stage larval survival (0–9 days) was not affected by feed HUFA levels. Second stage survival was significantly higher when larvae were fed copepods. Enrichment with 100 ppm SuperSelco greatly improved the survival of larvae that were fed brine shrimp. The even higher omega-3 fatty acids found in copepods appear to be important for survival of larvae under more stressful conditions.
Brine shrimp juveniles enriched with SuperSelco are a good food for postlarval mahimahi. Yolksac larvae of mahimahi are an even better food, promoting faster growth at less cost, for large scale mahimahi aquaculturists. Different batches of yolksac mahimahi larvae varied by a factor of 10 in their concentration of DHA, but always had the highest level of DHA as much as 40% of total fatty acids (FAs). These "high HUFA" batches of YSL also had the highest levels of EPA and total fatty acids. The data suggest that climate and broodstock age may have considerable influence on larval nutrition.     

PRELIMINARY REPORT ON THE AQUACULTURAL DEVELOPMENT OF THE DOLPHIN FISH,Coryphaena hippurus (LINNAEUS)

First and second generation (F₁ and F₂), laboratory reared juvenile Coryphaena hippurus were used in preliminary growth studies. Fish were stocked in circular tanks and fed a diet of chopped herring and squid. Initial size and age of fish used in these studies were as follows: 61 mm TL, 1.6 g, and 45 days old for F₁ and 87 mm TL, 5.95 g, and 65 days old for F₂. Mean size at 130 days of age was 560 mm TL and 1,305 g for F₁ and 540 mm TL and 1,150 g for F₂. Food conversion ratios were 3.05 and 2.9 4 for F₁ and F₂ fish, respectively.     

Characterizing egg quality and larval performance from captive mahi‐mahi Coryphaena hippurus (Linnaeus, 1758) spawns over time

Mahi‐mahi Coryphaena hippurus is a promising species for aquaculture development and has been used as a model species for oil toxicology and physiology studies. This species has one of the fastest growth rates of any marine teleost and a unique reproductive biology due to its high spawning frequency and reproductive energy allocation. These characteristics lend the species to being an excellent model for understanding broodstock nutrition for other high energetic pelagic species. In this study, egg morphometrics and larval survival were tracked over a 10‐week period from the initial capture of wild mahi‐mahi broodstock. Larval quality from subsequent spawns collected over time was quantified using larval survival activity indices (SAIs) as a metric to assess egg quality. Larval SAIs were maintained and did not significantly decrease (p < .05) over the time course of this study. A multiple linear regression based on the elapsed time in captivity of the broodstock, egg diameter and larval SAI at 1 dph provided the most accurate prediction of larval SAI at 3 dph (R² = 0.996 p < .05). There were strong positive correlations with larval SAIs at 1 and 3 dph and the key nutrients: eicosapentaenoic acid (C20: 5n‐3, EPA) and related fatty acid ratios, vitamin E and nearly all amino acids under investigation. This study demonstrated that larval survival was maintained over time due to the supply of these key nutrients in the broodstock diet.     

Myoliquefaction post-mortem ('milky flesh') due to Kudoa thyrsites (Gilchrist) (Myxosporea: Multivalvulida) in mahi mahi, Coryphaena hippurus L.

Abstract. Myoliquefaction occurred post-mortem in wild and cultured mahi mahi, Coryphaena hippurus L., stored on ice, and the flesh disintegrated upon cooking. The condition was associated with multifocal infection of muscle with Kudoa thyrsites (Gilchrist). Histiolysis is presumably due to enzymes excreted by the parasite, including collagenases, as the collagen fibres of the intermyotomal connective tissues were ruptured and hypochromatic. Myofibre changes were limited to hyaline degeneration and loss of myofibrillar detail. Kudoa thyrsites occurs commonly in Australian populations of the type host species, Thyrsites atun (Euphrasen), which represent a partly sympatric reservoir of infection for C. hippurus. The successful culture of C. hippurus may require selection of disease-free sites or use of filtered water supplies.     

Atlantic salmon, Salmo salar L., feed in Scottish coastal waters

Abstract. The stomach contents of 256 Atlantic salmon, Salmo salar L., of fork lengths 53–66cm, caught in bag nets on the Scottish west coast near Ullapool, were examined between June 1983 and July 1986. A total of 61 fish contained fish in the stomach or had faecal pellets containing fish bones in the gut. All recognizable whole fish were sandeels, Ammodytes marinus Raitt, ranging in size from 4.5 to 15cm. No evidence for crustacean or other non-fish prey items was found. Results indicate that feeding salmon were caught up to a certain cut-off point in June or early July, after which all salmon sampled were not feeding. It is suggested that either there is a local feeding stock of salmon or that fish feed during migration from the Faroe Isles or other possible distant water origins.     

Immunohistochemical characterization of malignant lymphoma in northern pike, Esox lucius L., from Estonian Baltic waters

Abstract. Twenty malignant lymphomas of northern pike, Esox lucius L., from the Baltic coast of Estonia were investigated immunohistochemically using rabbit anti-human polyclonal antibodies against lysozyme (LYS), alpha-1-antichymotrypsin (ACT) and S-100 protein. Based on the strongly positive reactions to LYS, ACT and S-100 found in a great number of histiocytes, two of these tumours were classified as histocytic diffuse malignant lymphomas. Furthermore, the weaker positive reaction to these antibodies detected in some of the histocytes in 10 other cases of diffuse malignant lymphoma indicates their histocytoid-lymphocytic origin. In addition, the lack of reaction to all antibodies used found in the remaining eight tumours, as well as their general morphological structure, allowed their diagnosis as lymphocytic diffuse malignant lymphomas. Thus, the immunohistochemical reactions to LYS, ACT and S-100 served as a tool for precisely distinguishing between the different types of lymphomas as well as for better understanding their origin.     

Escaped farmed Atlantic salmon, Salmo salar L., feeding in Scottish coastal waters

Escaped reared salmon, Salmo salar L., were distinguished from wild salmon in the catch of a coastal salmon fishery on the west coast of Scotland. The stomach contents of 54 escaped fish were examined to determine their recent feeding history and 19 (35%) were found to contain food. The predominant prey were juvenile whiting, Merlangius merlangus (L.), unidentified Gadidae and sandeels (Ammodytidae), although other fish and invertebrates, mainly post-larval hermit crabs (Paguridae), were recorded. All these prey are pelagic or semi-pelagic. These observations demonstrate that escaped salmon feed on natural prey in coastal waters and extend our knowledge of the diet of salmon in their marine phase.     

Studies on the pathology of ulcerative dermal necrosis (UDN) in Swedish salmon, Salmo salar L., and sea trout, Salmo trutta L., populations

Abstract. Continuous visual observations of the signs of development of UDN in fish kept in aquaria were correlated with light microscopical, transmission and scanning electron microscopical results. The initial signs of the disease are circles of pathologically-changed epidermis. The tight junctions of the squamous cells within these mucus-free areas disintegrate resulting in the loss of the protective function of the zonula occludens. Subsequently, the intercellular spaces dilate and communicate with the exterior. Necrosis of the epidermal cells due to hydromineral disturbances occur simultaneously with fungal infections and marked responses of the melanophores. It is suggested that the fungal infections are triggered by metabolites of the necrotic epidermal cells. The epidermal cells are shed and the fungus determines the further course of the disease which terminates in large ulcers covered with fungal hyphae. No substantial evidence for the presence of a virus could be recorded at any stage of the disease. It is concluded that the disease is a squames and the fungus appears as an opportunist which causes the eventual death of the fish.     

Ultrastructural pathology of Baltic salmon, Salmo salar L., yolk sac fry with the M74 syndrome

The ultrastructural pathology in liver, brain, skeletal and cardiac muscle of Baltic salmon yolk sac fry with the M74 syndrome is described. In the clinical stage of disease, the main pathological findings in the liver were a depletion of glycogen, condensation of nuclear chromatin, hydropic degeneration of mitochondria and a dilation of the bile canaliculi. In the terminal stage, additional findings were lipid accumulation and myelin whorls in the cytoplasm. The rough endoplasmic reticulum (RER) was degranulated and vesiculated and in some individuals, it formed concentric membranous whorls. Mitochondria showed several additional lesions, such as matrix densities, pleomorphism and cristae abnormalities. Skeletal myocytes were degenerated, and intracellular lipid accumulation was seen in the myocardium. In the brain, an increased frequency of cells exhibiting pyknosis or karryorhexis was recorded. The cytoplasm of these cells formed an amorphous mass of moderate density. The evaluation of brain and skeletal muscle was complicated by sporadic occurrence of pathological findings in the reference material, i.e. clinically healthy Baltic salmon yolk sac fry. As these yolk sac fry are suspected to have a subclinical thiamine deficiency, reference material in future studies should include salmon yolk sac fry from Atlantic populations or originating from reared broodstock.     

Acute tolerance of juvenile Florida pompano, Trachinotus carolinus L., to ammonia and nitrite at various salinities

The acute tolerance of juvenile Florida pompano Trachinotus carolinus L. (mean weight±SE=8.1±0.5 g) to environmental unionized ammonia‐nitrogen (NH₃‐N) and nitrite‐nitrogen (NO₂‐N) at various salinities was determined via a series of static exposure trials. Median‐lethal concentrations (LC₅₀ values) of NH₃‐N and NO₂‐N at 24, 48, and 96 h of exposure were calculated at salinities of 6.3, 12.5 and 25.0 g L^?1 at 28 °C (pH=8.23–8.36). Tolerance of pompano to acute NH₃‐N exposure was not affected by salinity, with 24, 48 and 96 h LC₅₀ values ranging from 1.05 to 1.12, 1.00 to 1.08 and 0.95 to 1.01 mg NH₃‐N L^?1 respectively. Regarding NO₂‐N, tolerance of pompano to this environmental toxicant was compromised at reduced salinities. Median‐lethal concentrations of NO₂‐N to pompano at 24, 48 and 96 h of exposure ranged from 67.4 to 220.1, 56.9 to 140.7 and 16.7 to 34.2 mg NO₂‐N L^?1 respectively. The results of this study indicate that juvenile Florida pompano are relatively sensitive to acute NH₃‐N and NO₂‐N exposure, and in the case of the latter, especially at lower salinities.