Morphological ontogeny of the gonad of three plectropomid species through sex differentiation and transition

The gonadal ontogeny through sex differentiation and transition of three protogynous coral trout species, Plectropomus leopardus , P. maculatus and P. laevis was described, based on anatomical and germinal differences along the length of the reproductive tract. Gonads of immature and mature females, sex changing individuals (transitionals) and males were examined. Specific anatomical features that were compared between sexual phases included the presence and structure of sperm sinuses, gonadal musculature and germinal cell types. All three coral trout species first differentiated as an immature female. The sexual pattern of P. leopardus and P. maculatus was concluded to be diandric protogynous hermaphroditism (males were derived from the juvenile phase as well as through sex change of mature females). Plectropomus laevis was found to be monandric as males were only derived through sex change in mature females. Structural changes did not occur concomitantly with the germinal changes associated with sex change in these Plectropomus species, which is atypical for protogynous species described to date. Precursory sperm sinuses in the dorso-medial region of the gonad were present, although non-functional, in a proportion of immature and mature females of all three species. These proportions, however, varied between species depending on the sexual pattern. The structural and germinal changes observed were hypothesized as anatomical adaptations that aid in minimizing time spent in the (non-reproductive) sexual transition phase and maximizing flexibility in male development in the diandric species.     

Auditory and olfactory abilities of larvae of the Indo-Pacific coral trout Plectropomus leopardus (Lacepède) at settlement

Auditory and olfactory abilities of settlement-stage larvae of the coral trout Plectropomus leopardus (Pisces: Serranidae) were tested electrophysiologically to determine if these senses are sufficiently developed to aid larvae in detection of settlement habitats on coral reefs. Plectropomus leopardus larvae detected sounds from 100 to 2000 Hz with hearing most sensitive at the frequencies of 100, 200 and 600 Hz. The olfactory response of P. leopardus was similar for the two amino acids tested and for the water conditioned by conspecifics. Auditory and olfactory abilities of P. leopardus are well developed at settlement-stage, and apparently sufficient to detect auditory and olfactory cues from reefs.     

Contrasting patterns of genetic structure in two species of the coral trout Plectropomus (Serranidae) from east and west Australia: introgressive hybridisation or ancestral polymorphisms

Inter-specific genetic relationships among regional populations of two species of grouper (Plectropomus maculatus and Plectropomus leopardus) were examined using mitochondrial and nuclear markers. mtDNA revealed contrasting regional inter-specific patterns whilst nuclear markers revealed contrasting patterns among markers, irrespective of region. In eastern Australia (EA) the species form a single mtDNA lineage, but the two species are reciprocally monophyletic in Western Australia (WA). This supports previous evidence for hybridisation between these species on the east coast. WA P. leopardus forms a sister relationship with the EA P. leopardus-maculatus clade while WA P. maculatus is more basal and sister to the P. leopardus lineages, indicating mtDNA does not suffer from incomplete lineage sorting for these species. In contrast, one of three nuclear markers (locus 7-90TG) differentiated the species into two reciprocally monophyletic clades, with no evidence of hybridisation or ancestral polymorphism. The remaining two nuclear markers (2-22 and ETS-2) did not separate these two species, while distinguishing other plectropomid species, suggesting incomplete lineage sorting at these nuclear loci. These results together with coalescence analyses suggest that P. leopardus females have hybridised historically with P. maculatus males and that P. maculatus mitochondria were displaced through introgressive hybridisation and fixation in the P. maculatus founder population on the Great Barrier Reef. The contrasting regional patterns of mtDNA structure may be attributed to Quaternary sea-level changes and shelf width differences driving different reef configurations on each coast. These reef configurations have provided opportunities for local scale interaction and reproduction among species on the narrower EA continental shelves, but not on the broader WA continental shelves.     

Comparative demography of commercially important species of coral grouper,Plectropomus leopardus and P. laevis,from Australia's great barrier reef and Coral Sea marine parks

Understanding the spatial and environmental variation in demographic processes of fisheries target species, such as coral grouper (Genus: Plectropomus), is important for establishing effective management and conservation strategies. Herein we compare the demography of Plectropomus leopardus and P. laevis between Australia's Great Barrier Reef Marine Park (GBRMP), which has been subject to sustained and extensive fishing pressure, and the oceanic atolls of Australia's Coral Sea Marine Park (CSMP), where there is very limited fishing for reef fishes. Coral grouper length-at-age data from contemporary and historical otolith collections across 9.4 degrees of latitude showed little difference in lifetime growth between GBRMP and CSMP regions. Plectropomus laevis populations in GBRMP reefs had significantly higher rates of total mortality than populations in the CSMP. Mean maximum lengths and mean maximum ages of P. laevis were also smaller in the GBRMP than in the CSMP, even when considering populations sampled within GBRMP no-take marine reserves (NTMRs). Plectropomus leopardus, individuals were on average smaller on fished reefs than NTMRs in the GBRMP, but all other aspects of demography were broadly similar between regions despite the negligible levels of fishing pressure in the CSMP. Similarities between regions in growth profiles and length-at-age comparisons of P. laevis and P. leopardus suggest that the environmental differences between the CSMP and the GBRMP may not have significant impacts on lifetime growth. Our results show that fishing may have influenced the demography of coral grouper on the GBR, particularly for the slower growing and longer lived species, P. laevis.     

Field and experimental studies of hybridization between coral trouts, Plectropomus leopardus and Plectropomus maculatus(Serranidae), on the Great Barrier Reef, Australia

Spawning aggregations of closely‐related coral trouts, Plectropomus leopardus and Plectropomus maculatus , were found to overlap in time and space on the Great Barrier Reef, thus providing opportunities for accidental hybridization by juxtaposition of heterospecific gametes. The relative abundance and mating strategy of coral trouts also favoured hybridization, since mates could be either rare in some habitats or monopolized by dominant fishes. In the latter case, sneak spawning may have occurred, even when behavioural barriers to reproduction ( e.g . assortative mating) were operational. When heterospecific gametes were experimentally mixed, fertilization occurred and hybrid larvae developed. It was concluded that there was considerable opportunity for natural hybridization between coral trouts of the genus Plectropomus .     

Classic approach revitalizes genomics: Complete characterization of a candidate gene for thermal adaptation in two coral reef fishes

Lactate dehydrogenase-B (ldh-b) encodes a metabolic enzyme (LDH-B) which plays an important role in maintaining aerobic performance and in thermal acclimation and/or adaptation of fish. As the first step in understanding the effect this enzyme has on the ability of tropical coral reef fishes to cope with thermal stress, we characterized both coding and non-coding regions of ldh-b in two congeneric perciformes, Plectropomus leopardus and Plectropomus laevis. Ldh-b was 4666 and 4539bp in length in P. leopardus and P. laevis, respectively, with coding regions comprising 1005bp in both species. We report a high level of sequence homology between the coding regions of ldh-b in these two species, with 98.1% identity of nucleotides corresponding to 100% amino acid identity between the deduced protein sequences. Comparison between non-coding (intron) regions of both species revealed the presence of several indels, despite the high level of homology observed (95.9% identity of intron nucleotides). Potential regulatory motifs and elements, including twenty-six simple sequence repeat motifs (mono-, di-, tri- and tetranucleotide) and twenty-three putative microRNA elements are identified within the introns of both species, further supporting recent demonstrations that such short motifs and elements exhibit widespread positioning throughout non-coding regions of the genome. This novel characterization of ldh-b in these two coral reef fishes allows for a wide range of future studies (e.g. analytical comparisons of ldh-b and LDH-B among different fish genera from different thermal environments and habitats).     

Reproduction of the inshore coral trout Plectropomus maculates (Perciformes: Serranidae) from the Central Great Barrier Reef, Australia

The reproductive biology of the serranid fish Plectropomus maculatus sampled from inshore waters of the Central Great Barrier Reef was studied based on histological analyses of gonad material. This species was shown to be a monandric protogynous hermaphrodite. The process of sex change foliowed the spawning period observed during September through November. Plectropomus: maculatus showed multiple spawning during this period. Sex change followed the usual protogynous mode with degeneration of ovarian germinal tissue accompanied by proliferation of male germinal tissue in the gonad. The sex structure of the sampled population was analysed based on age and size information. The size and age of first reproduction for females was 30.0cm s. L. and 2 years of age. The size and age of sex-transition was 35.4 cm s. L. and 4.4 years of age. The sex/size and sex/age relationships indicated that sex-change can occur over a broad range of sizes and ages. The sizes and age distributions of males and females P. maculates overlapped over 38% of the length range and over 42% of the maximum age observed.     

Physiological stress responses of two species of coral trout (Plectropomus leopardus and Plectropomus maculatus)

The physiological responses of two species of coral trout (Plectropomus maculatus and Plectropomus leopardus) to capture, shallow water and low salinity stressors were investigated. The responses of P. maculatus and P. leopardus to capture stress were characterised by rapid and transient increases in glucose, haemoglobin, haematocrit and lactate, as well as an equally dramatic but delayed increase in cortisol levels that persisted for at least 72 h. The magnitude and duration of the response to capture stress was very similar in both species. In contrast, the levels of cortisol, glucose, lactate, haemoglobin and haematocrit were generally elevated sooner and to higher levels in P. maculatus than in P. leopardus after exposure to shallow water stress. Coral trout exposed to reduced salinity showed minimal changes in cortisol, glucose, lactate, haemoglobin and haematocrit, but such changes were not characteristic of a non-specific response to stress. Thus, the physiological stress responses of coral trouts are species-specific and dependent on the nature of the stressor. This observation probably reflects different cortical processes in the brains of P. maculatus and P. leopardus-a result that may be related to the differential variability of the respective environments in which the two species habit.     

Diplectanids (Monogenea) parasitic on the gills of the coralgroupers Plectropomus laevis and P. leopardus (Perciformes, Serranidae) off New Caledonia, with the description of five new species and the erection of Echinoplectanum n. g.

Echinoplectanum n. g. is erected for diplectanids which have a male copulatory organ comprising a tubular sclerotised penis with a muscular reservoir at its proximal extremity and an protrusible cirrus, often with spiny ridges, at its distal extremity, and a female copulatory organ comprising a sclerotised vaginal sac, often with two thin tubes. All species have similar squamodiscs made of rows of rodlets, with the central rows forming closed circles, and haptoral parts with a similar shape but different measurements; they are distinguished on the basis of the size and morphology of the male copulatory organ and sclerotised vagina. Five new species are included in Echinoplectanum and are all parasites of coralgroupers, Plectropomus spp., off New Caledonia, South Pacific. Two are from P. laevis (Lacépède): E. laeve n. sp. (type-species) has a large elongate penis, 53[Formula: see text]m in length, a cirrus with spiny ridges and a spherical vagina with two long thin tubes; and E. chauvetorum n. sp. has a large elongate penis, 51[Formula: see text]m in length, a cirrus with thin spiny ridges, and a pear-shaped vagina with two short thin tubes. Three species are from P. leopardus (Lacépède): E. leopardi n. sp. has an elongate penis, 36[Formula: see text]m in length, an unspiny cirrus and a triangular vagina; E. pudicum n. sp. has a very small elongate penis 14[Formula: see text]m in length and no visible vagina; and E. rarum n. sp. has a short thick penis 18[Formula: see text]m in length and a ring-shaped vagina with two thin tubes. In addition, Diplectanum plectropomi Young, 1969, from P. maculatus off Western Australia, and D. echinophallus Euzet & Oliver, 1965 from Epinephelus marginatus in the Mediterranean Sea and Senegal, West Africa, both herein redescribed from the type-specimens, are transferred to Echinoplectanum, as E. plectropomi n. comb. and E. echinophallus n. comb., respectively. Six of the seven species of Echinoplectanum are parasitic in members of Plectropomus from the South West Pacific, but one (E. echinophallus) is a parasite of Epinephelus marginatus and has been recorded only from the Mediterranean and East Atlantic; it is suggested that Echinoplectanum is associated with Plectropomus, a basal genus among the epinephelines, and that host-switching to Epinephelus marginatus occurred, whose distribution extends from Europe to the Indian Ocean. Morphological characteristics of the copulatory organs suggest that a "chastity belt versus spiny penis" sperm competition pattern prevails in Echinoplectanum spp.     

豹纹鳃棘鲈体色变异的色素细胞差异分析

为了揭示豹纹鳃棘鲈(Plectropomus leopardus)体色变异机制,研究选取了不同体色个体的样本,利用石蜡切片、冰冻切片及体视显微镜观察等方法揭示不同皮肤部位色素细胞的类型、分布和数量的差异,并对应激和非应激状态下色素细胞的变化进行了研究。结果显示,黑色素细胞在背部和尾部分布比较密集,在腹部较为稀疏,黑色个体的黑色素细胞数量较红色个体多;在应激状态下个体能迅速发生体色变化,主要由于色素细胞快速扩张和收缩导致。研究为进一步揭示豹纹鳃棘鲈体色变异的分子机制和优良品种选育奠定了基础。     

A preliminary test of the transitional growth spurt hypothesis using the protogynous coral trout Plectropomus maculatus

Estimates of back-calculated size at age provided no evidence of a growth spurt following sexual transition in the protogynous serranid Plectropomus maculatus. The results suggested that mature females that had a large size at age early in life changed sex to male.     

Spatial and temporal variation in predation on reef fishes by coral trout (Plectropomus leopardus,Serranidae)

The diet of coral trout Plectropomus leopardus (Serranidae) was studied over a two year period at One Tree Island, Great Barrier Reef, Australia. Rapid visual counts demonstrated that P. leopardus were most abundant on the reef slope habitat and inner edge of the enclosed lagoon. Few P. leopardus were found at sites from inner lagoon. It was hypothesized that diet would vary among habitats, times and size classes of coral trout. Ninety-two percent of P. leopardus that contained prey had consumed fish and 87% had only eaten fish. Many types of reef fish were taken by P. leopardus (e.g. Pomacentridae, Scaridae, Blenniidae and Labridae). Most pelagic prey (Clupeidae and Engraulididae) were taken on the reef slope, while some prey were solely or pimarily taken in the lagoon (e.g. Blenniidae and crustaceans). Most pelagic prey were taken on the reef slope in summer by P. leopardus>250 mm (SL). Plectropomus leopardus (<200 mm) from the lagoon had a higher proportion of invertebrates in the diet than fish from the reef slope. Plectropomus leopardus of all sizes ate small fish, while largest fish generally consumed largest prey (especially adult scarids and labrids). I argue that interactions among multiple species of prey and predators need more attention, because piscivores may respond to prey in different ways according to habitat type as well as the number and type of other prey types present. Furthermore, different sizes of fish (e.g. coral trout) may impact assemblages of prey in different ways.     

Large‐scale,multidirectional larval connectivity among coral reef fish populations in the Great Barrier Reef Marine Park

Larval dispersal is the key process by which populations of most marine fishes and invertebrates are connected and replenished. Advances in larval tagging and genetics have enhanced our capacity to track larval dispersal, assess scales of population connectivity, and quantify larval exchange among no‐take marine reserves and fished areas. Recent studies have found that reserves can be a significant source of recruits for populations up to 40 km away, but the scale and direction of larval connectivity across larger seascapes remain unknown. Here, we apply genetic parentage analysis to investigate larval dispersal patterns for two exploited coral reef groupers (Plectropomus maculatus and Plectropomus leopardus) within and among three clusters of reefs separated by 60–220 km within the Great Barrier Reef Marine Park, Australia. A total of 69 juvenile P. maculatus and 17 juvenile P. leopardus (representing 6% and 9% of the total juveniles sampled, respectively) were genetically assigned to parent individuals on reefs within the study area. We identified both short‐distance larval dispersal within regions (200 m to 50 km) and long‐distance, multidirectional dispersal of up to ~250 km among regions. Dispersal strength declined significantly with distance, with best‐fit dispersal kernels estimating median dispersal distances of ~110 km for P. maculatus and ~190 km for P. leopardus. Larval exchange among reefs demonstrates that established reserves form a highly connected network and contribute larvae for the replenishment of fished reefs at multiple spatial scales. Our findings highlight the potential for long‐distance dispersal in an important group of reef fishes, and provide further evidence that effectively protected reserves can yield recruitment and sustainability benefits for exploited fish populations.     

Temporal variation in the diet of a coral reef piscivore (Pisces: Serranidae) was not seasonal

Seasonal and smaller scale temporal variations in the diet of the large predatory grouper Plectropomus leopardus were examined on the central Great Barrier Reef, Australia. In 5 months over a 2-year period, 742 P. leopardus (₅ cm standard length) were collected for stomach content analysis. Despite intensive sampling, identified prey were spread over 20 families and much of the dietary variation was considered to be stochastic. Most aspects of the diet of P. leopardus did not vary seasonally. Frequency, rates of feeding, and proportion of fish consumed were consistent throughout the study. Size of fish prey did not vary significantly between seasons. Pomacentridae, Caesionidae, Scaridae, and Labridae were four of the five most important prey families consumed and did not vary seasonally in the diet. Prey in the other family, the small-sized schooling Clupeidae, were consumed sporadically among months with no seasonal patterns. One less common prey family variedseasonally in the diet; Synodontidae, which are small voracious predators of fish recruits, were consumed by P. leopardus more in summer than winter. Although the diet of P. leopardus is not influenced by the seasonal influx of small fishes recruiting to reefs, these large piscivores may indirectly improve recruit survival by consuming small and abundant predators of new recruits.     

Encapsulated fish hooks from the stomachs of Plectropomus maculatus (Bloch) (Serranidae)

Encapsulated fish hooks were found free in the stomachs of Plectropomus maculatus (Bloch). The tissue surrounded only the ferrous part of the hooks which in each case was badly corroded, the brass swivel and plastic sleeve were undamaged. Histological examination showed that the hooks were first surrounded by dense collagen and then by vascularized smooth muscle.     

Widespread hybridization and bidirectional introgression in sympatric species of coral reef fish

Coral reefs are highly diverse ecosystems, where numerous closely related species often coexist. How new species arise and are maintained in these high geneflow environments have been long‐standing conundrums. Hybridization and patterns of introgression between sympatric species provide a unique insight into the mechanisms of speciation and the maintenance of species boundaries. In this study, we investigate the extent of hybridization between two closely related species of coral reef fish: the common coral trout (Plectropomus leopardus) and the bar‐cheek coral trout (Plectropomus maculatus). Using a complementary set of 25 microsatellite loci, we distinguish pure genotype classes from first‐ and later‐generation hybrids, identifying 124 interspecific hybrids from a collection of 2,991 coral trout sampled in inshore and mid‐shelf reefs of the southern Great Barrier Reef. Hybrids were ubiquitous among reefs, fertile and spanned multiple generations suggesting both ecological and evolutionary processes are acting to maintain species barriers. We elaborate on these finding to investigate the extent of genomic introgression and admixture from 2,271 SNP loci recovered from a ddRAD library of pure and hybrid individuals. An analysis of genomic clines on recovered loci indicates that 261 SNP loci deviate from a model of neutral introgression, of which 132 indicate a pattern of introgression consistent with selection favouring both hybrid and parental genotypes. Our findings indicate genome‐wide, bidirectional introgression between two sympatric species of coral reef fishes and provide further support to a growing body of evidence for the role of hybridization in the evolution of coral reef fishes.     

Increased accuracy of batch fecundity estimates using oocyte stage ratios in Plectropomus leopardus

Using the ratio of the number of migratory nuclei to hydrated oocytes to estimate batch fecundity of common coral trout Plectropomus leopardus increases the time over which samples can be collected and, therefore, increases the sample size available and reduces biases in batch fecundity estimates.     

Contrasting patterns of reef utilization and recruitment of coral trout (Plectropomus leopardus) and snapper (Lutjanus carponotatus) at One Tree Island, southern Great Barrier Reef

Patterns of abundance, age structure and recruitment of coral trout (Plectropomus leopardus) and snapper (Lutjanus carponotatus) were described in different environments, which varied in benthic cover, in a 12-yr study at One Tree Island. It was hypothesized that both taxa would show strong preferences to different environments and benthic cover and that patterns would be consistent through time. Plectropomus leopardus were abundant on the reef slope and seaward edge of the lagoon, where live coral cover was high, and recruitment was generally low, in all environments. The population was sustained by a trickle of recruits, and total abundance varied little after 10 to 25 yr of protection in a no-take area, suggesting P. leopardus had reached an environment-related carrying capacity. Protogynous P. leopardus recruited to shallow environments at sites with 20% or more hard live coral and age data indicated the abundance of fish on the reef slope was from redistribution. Most recruits of gonochoristic L. carponotatus (<150 mm Standard length, SL) were found in the lagoonal environments, and adults were rare on the reef slope. Abundance of recruit L. carponotatus and P. leopardus did not correlate with percent cover of live and soft coral within environments. Recruits of L. carponotatus were usually rare in all lagoonal environments, but in 2003, many recruits (80 to 120 mm SL) were found in lagoonal environments with low and high hard live coral cover. A substantial proportion of the population (age max 18 yr) was from strong recruitment events. In 2003 and 2004, total abundance of L. carponotatus was supported by 1 year class 51.7 and 41% respectively. The utilization of environments and types of substrata varied among taxa and in some cases among life-history stages. There was also temporal variation in the importance of some environments (e.g. Lagoon Centre).     

Patterns of recruitment and microhabitat associations for three predatory coral reef fishes on the southern Great Barrier Reef, Australia

This study examined recruitment patterns and microhabitat associations for three carnivorous fishes, Plectropomus maculatus, Lutjanus carponotatus and Epinephelus quoyanus, at the Keppel Islands, southern Great Barrier Reef, Australia. Habitat selectivity was highest for recruits that were found mostly with corymbose Acropora, predominantly on patches of live coral located over loose substrates (sand). Adults were more commonly associated with tabular Acropora. The proportion of P. maculatus (72 %) found with live corals was higher than for L. carponotatus (68 %) and E. quoyanus (44 %). Densities of recruits were highly variable among locations, but this was only partly related to availability of preferred microhabitats. Our findings demonstrate that at least some carnivorous reef fishes, especially during early life-history stages, strongly associate with live corals. Such species will be highly sensitive to increasing degradation of coral reef habitats.     

Aggregations of <Emphasis Type="Italic">Plectropomus areolatus</Emphasis> and <Emphasis Type="Italic">Epinephelus fuscoguttatus</Emphasis> (groupers,Serranidae) in the Komodo National Park,Indonesia: Monitoring and Implications for Management

Synopsis We identify fishery management implications from a long-term monitoring program focusing on spawning aggregations of high valued reef fish in Komodo National Park (KNP), Eastern Indonesia. Management objectives of KNP are not only to protect biodiversity, but also to conserve spawning stocks of high-valued commercial species for the replenishment of surrounding fishing grounds. We monitored two sites twice monthly over five years for two species of grouper, Epinephelus fuscoguttatus and Plectropomus areolatus. One site had an aggregation of both E. fuscoguttatus and P. areolatus, whereas the other site contained an aggregation of P. areolatus only. Over the five years monitoring period, aggregations typically formed during each full moon between September and February. Additionally, P. areolatus occasionally aggregated during new moons between April and July. We observed spawning only once, but because formation of aggregations were correlated to a higher incidence of behavior and signs indicative of reproduction and because most fish present were adults, it is likely that the formation of aggregations was associated with spawning. Over the five years monitoring period there was a reduction in mean fish size of up to 8 cm for P. areolatus, and a reduction in numbers of aggregating E. fuscoguttatus. Despite limited protection initiated in 2001, both sites are still heavily fished by local artisanal fishers. Because the observed reductions in size and in numbers could be caused by fishing pressure, managers should follow the precautionary principle by putting additional protective management in place. Since both species are relatively long-lived, at least five years of continued monitoring may be necessary to determine the outcome of management intervention. The variability in timing of aggregation in respect to season and moon phase in P. areolatus indicates that long-term monitoring must cover the entire year and both moon phases.