Seriola
Seriola is a genus of ray-finned fishes in the family Carangidae, commonly known as amberjacks, consisting of approximately nine extant species that inhabit temperate and subtropical marine waters globally.[1][2] These species are characterized by an elongate, fusiform, and compressed body form, with the upper jaw extending posteriorly to beneath the pupil, 11 to 16 gill rakers in adults, and a dorsal fin featuring seven to eight spines followed by soft rays.[2] Amberjacks are pelagic predators, primarily feeding on other fishes, and several species achieve large sizes, with the greater amberjack (S. dumerili) reaching up to 1.7 meters in length.[3][4] Notable species include the yellowtail amberjack (S. lalandi), valued in recreational fisheries and aquaculture for its fast growth and high market value, and the Japanese amberjack (S. quinqueradiata), which dominates marine finfish farming in Japan, accounting for over half of production in the early 2000s.[5][6] The genus holds economic significance in commercial fisheries, sport fishing, and expanding aquaculture efforts, particularly for species like S. lalandi and S. rivoliana, though challenges such as disease susceptibility and environmental impacts from farming persist.[7][8]Taxonomy and Classification
Etymology and History
The genus Seriola was established in 1816 by French zoologist Georges Cuvier in his classification of fishes, with the greater amberjack (Seriola dumerili) designated as the type species based on prior descriptions of Mediterranean specimens.[9][10] The type species had been initially described as Caranx dumerili by Antoine Risso in 1810 from Ligurian Sea catches, reflecting early reliance on regional fishery observations for taxonomic material.[3] The name Seriola derives from the Latin seriola, a diminutive of seria denoting a small earthenware jar or pot, though the precise rationale for applying this term to the fish remains undocumented in primary sources and may relate to vernacular Italian designations for amberjack-like species in Mediterranean markets.[11][12] Nineteenth-century expansions in global exploration prompted additions to the genus, including Seriola lalandi described by Achille Valenciennes in Cuvier and Valenciennes' 1833 work from Indo-Pacific and Atlantic specimens, with classifications refined through comparative morphology such as dorsal fin structure and squamation patterns.[12] These developments drew on specimens from transoceanic fisheries, underscoring how empirical data from commercial catches in subtropical waters shaped early delineations of Seriola's circumglobal scope prior to molecular analyses.[10]Phylogenetic Position
Seriola is classified within the family Carangidae, order Carangiformes, and subfamily Caranginae, distinguished morphologically by traits such as bifurcated dorsal fins (the first with 7–8 spines, the second with 1 spine and 20–30 rays), an anal fin with 2 detached spines followed by 1 spine and 17–25 rays, and a swim bladder that is elongated and partially detached posteriorly from the abdominal wall, adaptations linked to pelagic lifestyles.[13] These synapomorphies align Seriola with other carangines, supporting its position via comparative anatomy of jaw, fin, and vertebral structures that facilitate high-speed cruising and schooling.[14] Molecular evidence from mitochondrial cytochrome b (Cytb) and nuclear recombination activating gene 1 (RAG1) and rhodopsin (Rhod) sequences establishes the monophyly of Seriola as a robust clade within Carangidae, with Bayesian and maximum likelihood analyses yielding posterior probabilities and bootstrap supports exceeding 95% for internal nodes.[15] Phylogenetic reconstructions place Seriola sister to genera like Caranx and Trachinotus, diverging near the base of Caranginae during the Paleogene, with estimated crown-group diversification around 55 million years ago based on calibrated molecular clocks cross-validated against fossil calibrations.[16] Mitochondrial genome comparisons further corroborate this, showing genetic distances of 10–15% between Seriola and outgroup carangids, though some mitogenomic datasets indicate paraphyly when excluding nuclear loci, highlighting the need for multi-gene approaches to resolve incomplete lineage sorting.[17] Fossil records provide empirical calibration, with Seriola prisca from the Eocene Monte Bolca deposits (circa 50 million years ago) exhibiting vertebral and fin morphologies nearly identical to modern species, suggesting minimal morphological stasis since the early Paleogene radiation of carangids post-Cretaceous-Paleogene extinction.[18] Challenges to genus-level monophyly are limited, but species complexes like Seriola lalandi reveal cryptic lineages diverged over 2 million years ago via genomic SNPs and mtDNA, potentially driven by vicariance across ocean basins rather than hybridization, as evidenced by low inter-lineage gene flow.[19] These findings prioritize sequence divergence and fossil congruence over prior morphological ambiguities in hybrid zones.[20] ![Fossil specimen of Seriola prisca from Monte Bolca][center]Physical Characteristics
Morphology and Anatomy
Species of the genus Seriola possess an elongated fusiform body, moderately deep and laterally compressed, facilitating rapid locomotion in open water.[21] The dorsal profile is gently convex, while the ventral profile is more straight, with the body tapering to a slender caudal peduncle supporting a deeply forked caudal fin.[22] Scales are small and cycloid, covering the body except for a naked area anteriorly, and the lateral line is single, arching gently downward toward the caudal peduncle without scutes or keels.[23] [24] Fin configurations include two distinct dorsal fins: the first comprising 5-8 weak spines, often low or embedded in adults, and the second consisting of one spine followed by 27-40 soft rays; the anal fin features 2-3 detached spines anteriorly, followed by one spine and 19-33 soft rays, with both second dorsal and anal fins exhibiting a low anterior lobe in some species.[25] [26] Pectoral fins are shorter than the head length, and pelvic fins are positioned thoracic, with the fin rays aiding in maneuvering.[27] Coloration typically features olivaceous to bluish-grey dorsum transitioning to silvery-white ventrally, with dusky fins and, in adults of certain species like S. lalandi, a prominent amber or yellow stripe extending along the lateral line toward the caudal region.[28] [29] Sensory structures include a well-developed lateral line system for detecting hydrodynamic cues and relatively large eyes suited to low-light pelagic conditions.[24] Internally, Seriola species possess a physostomous swim bladder for buoyancy regulation, susceptible to barotrauma upon rapid decompression due to gas expansion.[30] The gill arches support rakers numbering 11-24, with higher counts in juveniles decreasing ontogenetically, functioning to strain ingested prey particles during active predation rather than true filter-feeding.[31] [32]Size, Growth, and Sexual Dimorphism
Species of the genus Seriola exhibit considerable variation in maximum size, with total lengths typically ranging from 1.5 to 2.5 meters and weights exceeding 40–100 kg in larger species. For instance, the greater amberjack (S. dumerili) attains a maximum total length of 190 cm and weights up to 80 kg, while the yellowtail kingfish (S. lalandi) can reach 2.5 m and 96.8 kg.[33][34] These maxima are documented from fishery captures and reflect asymptotic sizes in wild populations, influenced by environmental factors and species-specific genetics. Growth in Seriola is rapid, particularly during juvenile stages, with specific growth rates of approximately 7–8% per day observed in cultured S. rivoliana larvae and early juveniles.[35] In aquaculture settings, juveniles of species like S. lalandi and S. quinqueradiata demonstrate weight gains aligning with 1–2 kg per month under optimal conditions, driven by high-protein diets and controlled salinity.[36][37] Allometric patterns predominate, where length increases exponentially relative to age in early phases, transitioning to slower somatic growth; otolith analysis confirms this via annulus counts, linking incremental growth zones to seasonal deposition.[35][38] Sexual dimorphism in Seriola is subtle, with most species lacking pronounced external morphological differences, necessitating genetic or gonadal methods for sex identification.[39] However, in S. dumerili, females achieve larger sizes at given ages compared to males, indicating potential growth rate disparities post-maturity.[40] Age determination primarily relies on otolith microstructure, revealing lifespans of 7–12 years across species, with S. lalandi estimates reaching up to 8 years via ring counts, though wild captures suggest variability up to 12 years.[38][34] These estimates derive from validated otolith readings calibrated against known-age aquaculture cohorts, providing robust proxies for wild growth trajectories.[41]Distribution and Habitat
Global Range
Species of the genus Seriola inhabit subtropical and tropical waters across all major ocean basins, with core distributions spanning approximately 40°N to 40°S latitude based on verified capture records from ichthyological databases.[28][12] In the Atlantic Ocean, S. dumerili predominates, occurring from Nova Scotia, Canada (around 45°N) southward to Brazil (approximately 30°S), including the Gulf of Mexico and Caribbean Sea, with occasional vagrant records in temperate European waters documented via strandings.[28][3] The Indo-Pacific hosts multiple species with overlapping yet distinct ranges: S. quinqueradiata is confined to the northwest Pacific from the eastern Korean Peninsula and Japan to the Hawaiian Islands (roughly 25°N to 45°N), reflecting regional endemism supported by spawning patterns along the East China Sea continental shelf.[42] In contrast, S. dumerili extends across the Indo-West Pacific from South Africa and the Persian Gulf eastward to southern Japan, Hawaii, and New Caledonia (spanning about 35°S to 30°N).[28] S. lalandi occupies southern subtropical zones, including disjunct populations off South Africa, Australia, New Zealand, and Pacific islands like Easter and Pitcairn (down to 40°S), with genetic analyses indicating clustering that challenges full conspecificity across hemispheres.[12] In the eastern Pacific, S. dorsalis ranges from southern California (around 35°N) to Baja California Sur, Mexico (extending to 25°N), with juveniles occasionally stranding northward into temperate British Columbia waters during El Niño events.[43] Overall, while empirical occurrence data confirm these basin-specific patterns, modeled predictions of range expansion due to warming trends remain speculative without sustained observational validation.[43]Ecological Preferences
Species of the genus Seriola inhabit pelagic to epi-benthic reef-associated niches, with habitat selection primarily driven by temperature and salinity as revealed through trawl surveys and acoustic data in subtropical to temperate waters. These fishes prefer sea surface and bottom temperatures of 18–28 °C, with juveniles exhibiting optimal growth at approximately 26 °C and adults tolerating broader ranges up to 29.6 °C in observed distributions.[29][44][45] Salinities between 30 and 36 ppt align with their marine adaptations, supporting osmoregulation and growth while excluding hypo-osmotic stress below 25–29 ppt, as confirmed in tolerance experiments mirroring natural coastal conditions. Juveniles preferentially utilize nearshore nurseries, including Sargassum flotsam and low-relief coastal structures, which provide shelter and initial foraging grounds before offshore transitions.[46][47][48] Associations with oceanic currents and upwelling regions enhance prey aggregation, with stable isotope analysis (δ¹³C and δ¹⁵N) of muscle tissue indicating trophic reliance on nutrient-driven pelagic chains in these dynamic features.[49][50] Vertical habitat use spans surface waters to depths of 200 m or more, enabling exploitation of stratified prey distributions, in contrast to more bottom-oriented demersal carangids; archival tagging records depths varying seasonally with light and temperature cues.[51][52][29]Biology and Ecology
Reproduction and Development
Seriola species are gonochoristic, with distinct male and female individuals and no hermaphroditism, differing from protogynous forms in other Carangidae genera.[53]Reproduction occurs via batch spawning in warm seasons, primarily from May to July in Mediterranean populations when water temperatures range from 20–24 °C.[33] Females may release up to 30 batches per season.[33]
Fecundity correlates positively with female body size, as evidenced by gonadal analyses; larger females (14.6–27.2 kg) show batch fecundities of approximately 420,000 eggs kg⁻¹ body weight, versus 32,000 eggs kg⁻¹ in smaller ones. Total egg production per female reaches 4–9 million in Mediterranean stocks and 15–50 million in Atlantic ones, based on hydrated oocyte counts from wild samples.[33]
Eggs measure about 1.1 mm in diameter, are pelagic, and exhibit positive buoyancy due to oil globules, enabling drift in surface waters.[33]
Hatching occurs 30–34 hours post-fertilization at 23.5 °C, yielding larvae of 2.9 mm total length (TL).[54] Larvae maintain a planktonic existence, feeding exogenously from day 2, with swim bladder inflation by 120 hours post-hatch.[54] Metamorphosis, marked by fin ray formation and body shape stabilization, completes around 8 mm TL.[54] In mesocosm rearing, the larval phase extends to 40 days, reaching 40 mm TL, though wild durations may vary with environmental factors.[54]
Diet, Feeding, and Trophic Role
Species of the genus Seriola exhibit a carnivorous diet, primarily consisting of teleost fishes, cephalopods, and crustaceans, as determined through stomach content analyses across multiple populations.[55][56] In the Mediterranean, greater amberjack (S. dumerili) stomachs contained an average of two prey items per non-empty stomach, with teleosts dominating (e.g., clupeids and carangids), followed by cephalopods like octopods and squids, and crustaceans such as decapod shrimps.[57] Opportunistic predation is evident, with prey selection influenced by availability in pelagic and benthic habitats, though fish comprise over 70% of dietary volume in adults.[58] Juvenile Seriola shift toward smaller prey, including zooplankton and larval fishes, before transitioning to piscivory; young-of-the-year S. dumerili along Sicilian coasts consumed mysids, copepods, and small teleosts, reflecting ontogenetic changes in gape size and habitat use.[59] Stable isotope analyses (δ¹³C and δ¹⁵N) confirm this progression, with δ¹⁵N values increasing with size, indicating a move up the food web.[50] Seriola occupy a mean trophic level of approximately 4.0–4.5, positioning them as mid-to-upper level predators in pelagic ecosystems that exert top-down control on prey populations like schooling fishes and invertebrates.[42][60] For S. quinqueradiata, this level is estimated at 4.0 ± 0.65 based on food item composition, while juveniles of S. dumerili average 4.06 ± 0.80, underscoring their role in regulating lower trophic dynamics without dominating as apex predators.[61][62] Foraging involves ram ventilation, where forward swimming forces water over the gills and through the buccal cavity, supplemented by occasional ram suspension feeding for evasive or small prey; field videotapes of S. dumerili document open-mouth cruising at speeds enabling prey capture without suction, integrating locomotion with ventilation efficiency.[63] This strategy supports sustained predation in open water, with stomach fullness peaking post-dawn in some studies, aligning with diel prey availability.[64]Behavior and Migration
Juveniles of Seriola species, particularly S. quinqueradiata, form schools where aggressive interactions establish dominance hierarchies, with dominant individuals comprising 10-20% of the group and exhibiting higher frequencies of agonistic behaviors such as chasing and biting.[65] [66] In contrast, adults are typically solitary or occur in smaller aggregations, as evidenced by tagging studies showing dispersed movements during non-spawning periods.[52] Telemetry data from archival tags reveal diurnal vertical migrations in immature and adult Seriola, with individuals often occupying shallower depths (10-50 m) during the day and descending to 100-200 m at night, influenced by water temperature gradients and prey availability.[67] [52] These patterns include periodic dives and bursts of swimming activity, recorded in Sagami Bay for S. quinqueradiata juveniles, aligning with opportunistic foraging in the water column.[67] Spawning migrations have been tracked via tagging in multiple species; for S. quinqueradiata in the Japan Sea, adults undertake southward horizontal displacements from October to December, covering distances up to several hundred kilometers toward warmer southern waters.[68] [69] Similarly, S. dumerili in the East China Sea exhibits directed movements to putative spawning grounds extending north-south over 300 km, with tagged fish aggregating at depths of 50-150 m during peak spawning seasons from April to July, correlating with elevated sea surface temperatures above 24°C.[70] [71] These migrations are verified by pop-up archival tags recovering position data via light-based geolocation, demonstrating fidelity to coastal shelf edges rather than open-ocean trenches.[70]Predators, Parasites, and Diseases
Juvenile Seriola species serve as prey for larger pelagic predators, including yellowfin tuna (Thunnus albacares) and various shark species, which target schools in open waters.[72][73] Seabirds prey on smaller juveniles near the surface, while marine mammals such as California sea lions (Zalophus californianus) occasionally consume individuals in coastal regions.[74] These interactions reflect the genus's position in mid-trophic marine food webs, with predation intensity highest on early life stages due to schooling behavior and smaller body sizes.[72] Wild Seriola hosts a diversity of metazoan parasites, with monogeneans such as Benedenia seriolae and Zeuxapta seriolae commonly infesting gills and skin; surveys of S. lalandi in New Zealand identified 43 taxa, including these species with site-specific intensities up to moderate levels without reported mass mortality.[75][76] Nematodes, including Philometroides seriolae and Ophidascaris melanocephala, occur in internal tissues and ovaries, with records from S. dumerili in the eastern Atlantic showing prevalence tied to host size and migration patterns.[77][78] Myxosporeans like Unicapsula seriolae and Kudoa spp. form intramuscular cysts, observed in Japanese Seriola spp. with quantitative burdens linked to post-infection tolerance rather than acute pathology in wild hosts.[79][80] Parasite dynamics in wild Seriola demonstrate host tolerance, as S. dumerili exhibits lower susceptibility to myxosporean infections like Kudoa amamiensis compared to congeners, based on epizootiological field data from natural populations.[80] Blood flukes (Paradeontacylix spp.) parasitize vascular systems, with seven species specific to Seriola, though prevalence remains low in surveyed wild stocks without evident population-level impacts.[81] Bacterial diseases such as vibriosis, caused by Vibrio spp., occur sporadically in dense wild aggregations, correlating with environmental stressors like temperature fluctuations rather than endemic threats.[82] Empirical surveys indicate these infections rarely escalate to epizootics in open-ocean stocks, reflecting adaptive immune responses and low pathogen virulence in natural settings.[83]Species
Extant Species
The genus Seriola encompasses nine valid extant species, as recognized by FishBase, a comprehensive database of fish taxonomy drawing from peer-reviewed literature and expert validations.[43] These species are primarily distinguished by meristic counts (e.g., dorsal-fin spines ranging from 7–8, soft rays 18–22; anal-fin rays 15–19), body proportions, maximum attainable size, and geographic distribution, with genetic analyses providing additional resolution in cases of morphological similarity.[43]| Scientific name | Common name | Maximum length | Distribution | Diagnostic notes |
|---|---|---|---|---|
| Seriola carpenteri Mather, 1971 | Guinean amberjack | 72.5 cm TL | Eastern Atlantic | Smaller size; 8 dorsal spines, 19–20 dorsal soft rays; restricted range off West Africa.[84] |
| Seriola dumerili (Risso, 1810) | Greater amberjack | 190 cm TL | Circumglobal tropics | Large body; 7–8 dorsal spines, 18–20 soft rays; prominent anterior dorsal fin.[28] |
| Seriola fasciata (Bloch, 1793) | Lesser amberjack | 67.5 cm FL | Western Atlantic | Moderate size; 7–8 dorsal spines; juveniles with prominent dark bands.[85] |
| Seriola hippos Günther, 1876 | Samson fish | 150 cm TL | Indo-Pacific | Robust form; 8 dorsal spines; greenish hue with yellow stripe.[86] |
| Seriola lalandi Valenciennes, 1833 | Yellowtail amberjack | 250 cm TL | Circumglobal subtropics | Elongated yellow tail stripe; lacks scutella on caudal peduncle; 8 dorsal spines, 19–21 soft rays.[12] |
| Seriola peruana Steindachner, 1881 | Fortune jack | 57 cm FL | Eastern Pacific | Smallest in genus; 7 dorsal spines; off Peru and Chile.[87] |
| Seriola quinqueradiata Temminck & Schlegel, 1845 | Japanese amberjack | 150 cm TL | Northwest Pacific | Five dorsal fin elements prominent; 8 spines, 19–20 rays; temperate waters.[88] |
| Seriola rivoliana Valenciennes, 1833 | Longfin yellowtail | 160 cm FL | Circumglobal Indo-West + eastern Atlantic | Elongated pectoral fins; 7–8 dorsal spines; tropical reefs.[89] |
| Seriola zonata (Mitchill, 1815) | Banded rudderfish | 75 cm TL | Western Atlantic | Juveniles with 5–7 dark bands; 8 dorsal spines; associates with large hosts.[90] |