Osteological development of Dentex dentex (Osteichthyes: Sparidae): dorsal, anal, paired fins and squamation

The osteological development of dorsal, anal and paired fins and the squamation in common dentex, Dentexdentex (Linnaeus, 1758), was studied under extensive larval rearing conditions. The ontogeny of the fins was determined in three stages: (1) the yolk-sac and the early larval stage (up to 6.7 mm in vivo total length, TL), in which the majority of the elements of the pectoral fins and the predorsals, dorsal and anal proximal pterygiophores formed; (2) the late larval stage (up to 11.6 mm TL), in which the majority of the pectoral lepidotrichia, the lower extrascapulae, all the elements of the pelvic fins, as well as the lepidotrichia, spines and the distal radials of the rest fins developed; and (3) the metamorphosis stage (up to 24.0 mm TL), when the upper extrascapulae formed and the pectoral lepidotrichia attained their full count. The ontogeny of squamation was carried out during the metamorphosis stage; it started at 13.4 mm TL with laterally symmetric points on the middle of each side of the body, followed by one ventral centre (15.6 mm TL) which was located anterior to the pelvic fins, and two bilateral pairs of centres which appeared on the head (17.8 and 21.2 mm TL). The results are discussed from a functional viewpoint and in comparison with the fin and scale ontogeny of other teleosts. Received: 1 March 2000 / Accepted: 20 September 2000     

Sexual maturity and hermaphroditism of the red porgy Pagrus pagrus (Teleostei: Sparidae)

Gonadal changes related to sexual maturity were examined by histology in reared populations of the red porgy Pagrus pagrus L., aged 0.5 to 6.5 years. More than 50% of red porgies were mature at the age of 4 years although some individuals were already mature at the age of 3, as indicated by changes in the gonadosomatic index, plasma levels of vitellogenin, 17β-estradiol and testosterone in females and males. Sex frequency distribution analysis in relation to the age and histological analysis of the gonads indicated the presence of males originated from the sex change of adult functional females. P. pagrus is a protogynous species. Some females had not changed sex up to the age of 6.5 years. Received: 16 July 1998 / Accepted: 29 April 1999     

Seasonal cycle of gonadal development and serum levels of vitellogenin of the red porgy, Pagrus pagrus (Teleostei: Sparidae)

Histological examination of gonads of female and male red porgy, Pagrus pagrus, reared in captivity, was carried out in order to describe the main gonadal changes related to gametogenesis and the seasonal changes of environmental factors. The gonadosomatic index (GSI) and the concentration of serum vitellogenin (VTG) were also determined. The frequency distribution of gonad development stages and the GSI and vitellogenin concentration during the annual cycle indicated the separation of the female and male reproductive cycles into three main periods. The autumn period when gametogenesis begins (October-November), the period of exogenous vitellogenesis (December-March) or spermiation (December-March), and the spawning season (March-May). The spawning period coincided with an increase in temperature (15-19°C) and daylength. Serum levels of vitellogenin rose significantly in January, reached a peak at the beginning of the spawning period (March, 405.5 µg ml^-1) and remained high until the end of the spawning period (May).     

Connectivity between marine reserves and exploited areas in the philopatric reef fish Chrysoblephus laticeps (Teleostei: Sparidae)

‘No-take’ marine protected areas (MPAs) are successful in protecting populations of many exploited fish species, but it is often unclear whether networks of MPAs are adequately spaced to ensure connectivity among reserves, and whether there is spillover into adjacent exploited areas. Such issues are particularly important in species with low dispersal potential, many of which exist as genetically distinct regional stocks. The roman, Chrysoblephus laticeps, is an overexploited, commercially important sparid endemic to South Africa. Post-recruits display resident behavior and occupy small home ranges, making C. laticeps a suitable model species to study genetic structure in marine teleosts with potentially low dispersal ability. We used multilocus data from two types of highly variable genetic markers (mitochondrial DNA control region and seven microsatellite markers) to clarify patterns of genetic connectivity and population structure in C. laticeps using samples from two MPAs and several moderately or severely exploited regions. Despite using analytical tools that are sensitive to detect even subtle genetic structure, we found that this species exists as a single, well-mixed stock throughout its core distribution. The high levels of connectivity identified among sites support the findings of previous studies that have indicated that inshore MPAs are an adequate tool for managing overexploited temperate reef fishes. Even though dispersal of adult C. laticeps out of MPAs is limited, the fact that the large adults in these reserves produce exponentially more offspring than their smaller counterparts in exploited areas makes MPAs a rich source of recruits. We nonetheless caution against concluding that the lack of structure identified in C. laticeps and several other southern African teleosts can be considered to be representative of marine teleosts in this region in general. Many such species are represented in more than one marine biogeographic province and may be comprised of regionally adapted stocks that require individual management.     

Development of the skull in Dentex dentex (Osteichthyes: Sparidae)

The development of the skull skeleton in common dentex, Dentex dentex (Linnaeus, 1758), was studied under extensive rearing conditions. Skull ontogeny started after hatching and went through three stages: (a) the yolk-sac (during the phase of no growth) and the early larval stage (up to 6.9 mm in vivo total length, TL) in which the majority of the skull elements formed; (b) the late larval stage (up to 11.3 mm TL) in which the basisphenoid, infraorbital 1, parethmoids, nasals, ethmoids, pleurosphenoids, opisthotics and orbitosphenoids developed; and (c) the metamorphosis stage (up to 24.0 mm TL) during which the remaining infraorbitals formed, the cartilaginous areas of the neu- roskull regressed and the sclerotics started to ossify. Teeth first appeared at 5.2 mm TL, and gill filaments formed between 5.7 and 6.9 mm TL. The results are discussed in view of the ontogeny of functions and in comparison with the skull ontogeny of other teleosts. Received: 1 July 1998 / Accepted: 1 September 1999     

Feeding macroecology of territorial damselfishes (Perciformes: Pomacentridae)

The present study provides the first analysis of the feeding macroecology of territorial damselfishes (Perciformes: Pomacentridae), a circumtropical family whose feeding and behavioral activities are important in structuring tropical and subtropical reef benthic communities. The analyses were conducted from data collected by the authors and from the literature. A strong positive correlation was observed between bite rates and sea surface temperature (SST) for the genus Stegastes. A negative correlation was found between bite rates and mean body size for the genera Stegastes and Pomacentrus, but this relationship was not significant when all territorial pomacentrids were analyzed together. A negative correlation between body size and SST was observed for the whole group and for the genera Stegastes, and Pomacentrus. No relationship was found between territory size and feeding rates. Principal Components Analysis showed that differences in feeding rates accounted for most of the variability in the data. It also suggested that body size may be important in characterizing the different genera. In general, tropical species are smaller and have higher bite rates than subtropical ones. This study extended the validity of Bergmann’s rule, which states that larger species or larger individuals within species occur towards higher latitudes and/or lower temperatures, for an important group of reef fishes. The identification of large-scale, robust ecological patterns in the feeding ecology of pomacentrid fishes may establish a foundation for predicting large-scale changes in reef fish assemblages with expected future changes in global SST.     

Ontogeny and allometric plasticity of Dentex dentex (Osteichthyes: Sparidae) in rearing conditions

The ontogeny of Dentex dentex (Linnaeus, 1758) was studied comparatively under extensive and semi-extensive rearing conditions. The exotrophic phase was divided into three distinct developmental stages (a) larval, from feeding onset up to 10 mm total length (TL); (b) metamorphosis, from 10 mm TL up to 24 mm TL; and (c) further juveniles. The majority of all ontogenic changes was expressed during the larval stage and integrated during the metamorphosis stage. The juvenile stage was characterized by developmental stability. The normal development of D. dentex was seriously affected by the rearing conditions applied during the early exotrophic phase. The two differently reared populations followed similar developmental patterns of general morphology, pigmentation and behaviour, but they presented high developmental plasticity where allometric growth was concerned. Rearing conditions influenced both the boundaries of the sequential stages (in 50% of the morphometric ratios) and the allometry coefficient of each morphometric character in the various developmental stages (in 80% of the characters). The results are discussed with respect to the ontogeny of the functional morphology under both ecological and aquaculture considerations. Received: 1 August 1998 / Accepted: 1 September 1999     

Lipid storage and composition in tropical surgeonfishes (Teleostei: Acanthuridae)

The lipid composition of tropical marine reef fishes is poorly known, despite their use as food by local human populations and recent interest in health-related benefits of fish lipids. We examined the composition of lipids from epaxial muscle, liver, and two storage sites [mesenteries surrounding the gut (intraperitoneal fat, IPFs) and retroperitoneal fat bodies (FBs) posterior to the peritoneal cavity] in three species of surgeonfishes from Ishigaki Island, Japan: Naso lituratus (Bloch and Schneider, 1801), Acanthurus lineatus (Linnaeus, 1758), and A. bariene (Lesson, 1830). Triacylglycerols dominated all samples of neutral lipid and constituted ≥ 99% of FBs and IPFs. Polar lipids generally contained large fractions of phosphatidylethanolamine and phosphatidylcholine. Quantified fatty acids ranged in length from C₁₄ to C₂₄. C₁₆ fatty acids prevailed (>35% of neutral fatty acids, >23% of polar fatty acids), although C₁₈ (>16 and >14%, respectively) and C₂₀ acids (>8 and >19%, respectively) were also common. Saturated fatty acids, dominated by palmitic acid (16:0), comprised 38.7 to 50.7% of acids from neutral lipids and 30.8 to 41.1% from polar lipids. The most common monounsaturated acids were 18:1n9 and 20:1n9. Polyunsaturated acids were prevalent in polar lipids (especially 20:4n6, 20:5n3, 22:2n3, 22:5n3, 22:5n6 and 22:6n3). Common polyunsaturated acids of neutral lipids were 18:2n6, 18:4n3, several n-3 and n-6 C₂₀ acids, 22:2n3 and 22:5n3. IPF and FB were almost identical across species, and lipids of fat bodies (IPFs, FBs) were more similar to those of muscle than those of liver for all three species. The FBs appear to constitute an accessory storage site, which overcomes constraints on lipid storage imposed by a small, inflexible abdominal cavity that contains both viscera and consistently voluminous gut contents. Fatty acid signatures indicate that largely overlooked epiphytic or epilithic diatoms contribute significantly to lipid acquisition. The combination of large quantities of both saturated and n-3 and other polyunsaturated fatty acids in surgeonfishes, in contrast to low saturates and high polyunsaturated acids in lipids of commercially important cool-water fishes, suggests that a study of dietary effects of fish lipids on human inhabitants of the tropics may be instructive insofar as human health and nutrition are concerned. Received: 16 March 1998 / Accepted: 6 August 1998     

Polymorphism in gigantobacterial symbionts in the guts of surgeonfish (Acanthuridae: Teleostei)

The morphology and partial cytology of a group of bacteria-related organisms from the guts of surgeonfish are described. These gigantobacteria symbionts are encountered in the guts of various species of this fish family throughout the Indo-Pacific region and the Red Sea. They have been tentatively grouped and placed in a “family”, Epulopiscidae, according to the first species described, Epulopiscium fishelsoni Montgomery and Pollak, 1988. In addition to a morphological comparison between the various forms from different species of surgeonfish, suggestions are presented with regard to their possible morphological diversification during evolutionary and host-species specificity. Received: 10 June 1998 / Accepted: 29 October 1998     

Histology and ultrastructure of the skin of Lepadichthys lineatus (Gobiesocidae: Teleostei)

The skin of the Red Sea clingfish Lepadichthys lineatus Briggs, 1966, which lives on shallow-water crinoids, consists of a continuous layer of giant mucus-producing cells. Upon stimulation, these cells are able, in seconds, to envelope the fish entirely with a thick layer of their secretion. The cells are 75 to 290 high, and are enveloped by septa of compressed epithelium. They rest on a strong collagenous layer, and extend to the skin surface, where they open. The nuclei of the giant cells are large, and irregularly shaped; their cytoplasm has a very extensive endoplasmic reticulum and undergoes deep structural changes during maturation. Their ability to produce large amounts of mucus seems to be an adaptive device to protect the fish from contact with the rough surface of the crinoid host.     

Genetic divergence and phylogenetic inferences in five species of Mugilidae (Pisces: Perciformes)

Allozyme electrophoresis was used to compare the genetic divergence of global populations of Mugil cephalus Linnaeus, 1758 and two congeneric [M.␣curema Cuvier & Valenciennes, 1836; M. gyrans (Jordan & Gilbert, 1885)] and two more distantly related [Liza ramada (Risso, 1826); Xenomugil thoburni (Jordan & Starks, 1896)] species on the basis of 18 enzyme loci. The amount of genetic divergence among the species examined is in agreement with their present systematic status, the differences being larger among non-congeneric species than among species of the same genus. Intraspecific genetic distances in M. cephalus (average Nei's D= 0.154), although higher than those reported for conspecific populations of fish, appear to be small when compared to the interspecific values among mugilid species (0.821 ≤ Nei's D ≤ 1.744). Phylogenetic trees obtained by genetic distance methods and discrete character parsimony analysis were of similar topology, except for the relationships within the genus Mugil and for the arrangement of M. cephalus populations. Received: 7 April 1997 / Accepted: 4 February 1998     

Feeding of laboratory-reared larvae of the sea bream Archosargus rhomboidalis (Sparidae)

Feeding by larvae of the sea bream Archosargus rhomboidalis (Linnaeus) was investigated from late September, 1972 to early May, 1973 using laboratory-reared larvae. Fertilized eggs were collected from plankton tows in Biscayne Bay, and the larvae were reared on zooplankton also collected in plankton nets. Techniques were developed to estimate feeding rate, food selection, gross growth efficiency, and daily ration. Daily estimates of these were obtained through 16 days after hatching at rearing temperatures of 23°, 26°, and 29°C. Feeding rate increased exponentially as the larvae grew, and increased as temperature was raised. At 23°C larvae began feeding on Day 3, at 26° and 29°C larvae began feeding on Day 2. Feeding rates at initiation of feeding and on Day 16 were, respectively: 23°C, 7.16 food organisms per larva per hour (flh) and 53.78 flh; 26°C, 7.90 flh and 168.80 flh; 29°C, 17.62 flh and 142.07 flh. Sea bream larvae selected food organisms by size. At initiation of feeding they selected organisms less than 100 m in width. As larvae grew they selected larger organisms and rejected smaller ones. The major food (more than85% of the organisms ingested) was copepod nauplii, copepodites, and copepod adults. Minor food items were barnacle nauplii, tintinnids, invertebrate eggs, and polychaete larvae. Mean values for gross growth efficiency of sea bream larvae ranged from 30.6% at 23°C to 23.9% at 29°C. Mean values for daily ration, expressed as a percentage of larval weight, ranged from 84% at 23°C to 151% at 29°C and tended to decline as the larvae grew.This paper is a contribution from the Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida, USA     

Social organization and sexual pattern in the Mediterranean parrotfish Sparisoma cretense (Teleostei: Scaridae)

We examined the social organization and reproductive pattern of a population of Sparisoma cretense L. at Lampedusa Island (Italy). During the breeding season (July to September) individuals occur either in territorial or in non-territorial groups, which quantitatively differ with respect to use of space, sex-ratio and sexual activity. Territorial groups consist of one male plus one to three females, whereas in non-territorial groups as many as 54 fish share a common area. Among non-territorial groups, variations, in both sex-ratio and behavior, suggest they could represent either feeding aggregations or reproductive aggregations. Spawning, always in pairs, occurs daily in a short period of time before dusk and has been observed only in territorial groups. Group spawning has never been observed, but another alternative mating tactic, streaking on pair spawning, was recorded. In the non-breeding season fish do not aggregate in organized social units. Histological examination of gonads showed that adults are larger than 12 cm total length. Females have an asynchronous ovary, typical of species spawning several times during the breeding season. Males show secondary testes, indicating that their gonads develop ovaries as juveniles, which are later redifferentiated into functional testes. Histological and demographic data seem to indicate that, as in other species of this genus, prematurational sex-change occurs. The sexual pattern appears to be essentially gonochoristic, but the potential for sex-change is not excluded. Received: 5 January 1999 / Accepted: 22 June 1999     

Population size and mortality of juveniles of the marine teleost Rhabdosargus holubi (Pisces: Sparidae) in a closed estuary

The populations of juvenile Rhabdosargus holubi (Steindachner) present in a South-east African estuary which was closed off from the sea in 1971 and 1972 were estimated using mark-recapture techniques. The estuary opened to the sea in August, 1971, and did not close again until January, 1972, by which time a different population of R. hulubi had established itself. The Petersen method and a multiple markrecapture method gave comparable population estimates. Catch per unit effort data supported the trends shown by the population estimates. At the beginning of 1971, the population was about 55,000 but, at the end of 7 months, had declined to 11,000, the monthly mortality varying between 9 and 49%. Mortality was insignificant in 1972, when a different population of approximately 12,000 individuals was present. Evidence is presented to show that the decline in numbers in 1971 was possibly due to bird predation, and was densitydependent.     

Twilight migrations and foraging activities of the copper sweeper Pempheris schomburgki (Teleostei: Pempheridae)

During 1976 and 1977, movements and foraging activities of Pempheris schomburgki were studied on the shallow coral reefs of northeastern St. Croix, U.S. Virgin Islands. P. schomburgki emerge from daytime refuges on the backreef at about local sunset. Fifteen to 20 min after sunset, local milling groups move beyond the confines of the reef and assemble into larger groups. Twenty-five to 30 min after sunset they move in several waves along complex routes through the reef to forereef feeding grounds. Migrations of up to 1 km occur along the forereef. The reverse sequence occurs in the morning, but is earlier with respect to ambient light levels. The principal stages of these activities appear to be triggered by a combination of absolute light level, rate of change of light and state of adaptation of the eye. Migrating aggregations gradually split up into small, well-dispersed feeding groups, relatively evenly spaced along the forereef. Few individuals feed on the backreef. The principal available food consists of meroplanktonic crustaceans not available during the daytime. P. schomburgki mainly select the larger-sized individuals (mean length 5 to 6 mm), although some particles less than 1 mm are taken. These events probably represent adaptations to optimize diurnal sheltering sites, feeding grounds and the avoidance of predator activity.     

Seasonality in gonads,fat deposits and condition of tropical surgeonfishes (Teleostei: Acanthuridae)

Lipids are stored in mesenteries surrouding the gut and in paired, retroperitoneal fat bodies dorsal to the anal fin in at least 24 surgeonfishes representing 5 genera (Acanthurus, Ctenochaetus, Naso, Prionurus, Zebrasoma) from Western Mexico, Hawaii, French Polynesia, Great Barrier Reef and the Red Sea. In A. nigrofuscus from the Red Sea and C. striatus from French Polynesia, fat stores and condition index (K=100 W/L ³) increased during cool seasons, several months before gonads developed, and declined with the onset of gonadal development. Fat bodies and mesenteric fat deposits developed in all sizes of A. nigrofuscus and C. striatus, and condition paralleled seasonal changes in fat deposits. Gonads of A. nigrofuscus developed in specimens of 76 to 159 mm standard length (SL), while they developed in C. striatus only at lengths>170 mm total length (TL) for females and 195 mm TL for males. Mesenteric fats and fat bodies exhibited similar changes in size, and did not differ in occurrence of major groups of lipids or their relative prevalence. The relative proportions of the major lipid classes differed, however, between these storage sites and other tissues. Muscle, liver and gonads contained less triacylglycerol relative to cholesterol and polar lipid than did mesenteric or fat body lipids. Energy and nutrients acquired during cool saasons with short feeding days appear to support reproductive events during warm seasons, when feeding during longer days fails to meet demands. Fat stores and condition continue to decline beyond the reproductive season until winter.     

Genetic variation in seven goby species (Perciformes: Gobiidae) assessed by electrophoresis and taxonomic inference

Data on the electrophoretic patterns of 20 enzyme loci were used to investigate relationships among seven Mediterranean goby species. The study evidenced different levels of genetic variability among the species. On the whole, the degrees of genetic differentiation were consistent with the current taxonomic recognition of species and genera. Phenetic and phylogenetic analyses agreed in clustering the samples in three groups, i.e. the Gobius (including Zosterisessor ophiocephalus), the Lesueurigobius species and Pomatoschiarua minutus. The taxa analysed probably evolved following the complex geological and climatic events that have been affecting the Mediterranean basin ever since the Miocene. Received: 20 June 1998 / Accepted: 5 February 1999     

Identification of tenuis of four French Polynesian Carapini (Carapidae: Teleostei)

Four species of adult Carapini (Carapidae) occur on Polynesian coral reefs: Encheliophis gracilis, Carapus boraborensis, C. homei and C. mourlani. Samples collected in Rangiroa and Moorea allowed us to obtain different tenuis (larvae) during their settlement phases or directly inside their hosts. These were separated into four lots on the basis of a combination of pigmentation, meristic, morphological, dental and otolith (sagittae) features. Comparison of these characters with those of the adults allows, for the first time, taxonomic identification of these tenuis-stage larvae.     

New expansions in old clades: population genetics and phylogeny of Gnatholepis species (Teleostei: Gobioidei) in the Pacific

Species of the reef goby genus Gnatholepis exhibit enormous geographic ranges with little evidence of population segregation detectable based on mitochondrial DNA. To determine if genetic differentiation is evident with more rapidly evolving markers, seven microsatellite loci were screened from the species Gnatholepis anjerensis and G. scapulostigma and population segregation was tested among fish from across the South Pacific. Both AMOVA and pairwise F _ST analyses showed that, in concordance with previous mitochondrial results, most genetic variance occurs within individual populations, as population differentiation is evident only over the largest distances (>3,700 km). This result is contrasted with previous studies demonstrating that despite their relatively long larval periods, some gobiid fishes exhibit population differentiation on small (<100 km) geographic scales. Coalescence analysis showed that current Pacific populations of these species originated in the Pleistocene, presumably related to sea level fluctuations associated with episodes of glaciation. However, rate analysis based on a phylogeny of Gnatholepis species indicates that the species themselves are much older, consistent with a complex history of rapid, short-term population contractions and expansions, with corresponding rapid dispersal.     

A new fat body associated with the gonad of surgeonfishes (Acanthuridae: Teleostei)

Adults of nine species of surgeonfishes (Acanthuridae) from the Red Sea, Israel and the Eastern Tropical Pacific off Mexico possess previously undescribed fat bodies associated with both male and female gonads. These structures are unique in that they are external to the abdominal cavity, are composed almost entirely of highly-saturated triacylglycerols, and appear to have close circulatory connection with the gonads. In all species except one, the fat bodies rest in triangular pockets between the trunk musculature and skin, which extend posteriorly just above the anal fin base. The composition, arrangement and dynamics of the fat bodies suggest that they support the active gonad during a spawning season that lasts, in one species, from May to September.