Tropical Damselfish Research Articles

Two pathways regulate insulin-like growth factor genes in the brain and liver of the tropical damselfish Chrysiptera cyanea: A possible role for melatonin in the actions of growth and thyroid hormones

External and internal factors are involved in controlling the growth of fishes. However, little is known about the mechanisms by which external factors trigger stimulus signals. This study explored the physiological roles of melatonin in the transcription of growth-related genes in the brain and liver of Chrysiptera cyanea, a tropical damselfish with long-day preference. In brain samples of this species collected at 4-h intervals, the transcript levels of arylalkylamine N-acetyltransferase2 (aanat2), the rate-limiting enzyme of melatonin synthesis, and growth hormone (gh) peaked at 20:00 and 00:00, respectively. Concomitantly, the transcript levels of insulin-like growth factors (igf1 and igf2) in the brain and liver were upregulated during the scotophase. Levels of iodothyronine deiodinases (dio2 and dio3), enzymes that convert thyroxine (T4) to triiodothyronine (T3) and reverse T3, respectively, increased in the brain (dio2 and dio3) and liver (dio2) during the photophase, whereas dio3 levels in the liver showed the opposite trend. Fish reared in melatonin-containing water exhibited significant increases in the transcription levels of gh and igf1 in the brain and igf1 in the liver, suggesting that growth in this fish is positively regulated by the GH/IGF pathway on a daily basis. Melatonin treatment also stimulated the transcript levels of dio2 and dio3 in the liver, but not in the brain. Fish consuming pellets containing T3, but not T4, showed significant increases in gh and igf1 in the brain and igf1 and igf2 in the liver, suggesting that the intercellular actions of the TH/IGF pathway have an impact on growth on a daily basis. In summary, IGF synthesis and action in the brain and liver undergo dual regulation by distinct hormone networks, which may also be affected by daily, seasonal, or nutritional factors.

Melatonin influences reproduction in the sapphire devil Chrysiptera cyanea via regulation of dopamine 2b receptor transcription

Melatonin and dopamine participate in the regulation of reproduction-related hormone/peptide synthesis and secretion at the hypothalamic–pituitary–gonadal axis in fish. Here, we report a unique reproduction-related interaction of melatonin and dopamine in the brain of the sapphire devil Chrysiptera cyanea, a tropical damselfish with a long-day preference. We examined the expression of arylalkylamine N-acetyltransferase 2 (aanat2)—a rate-limiting enzyme of melatonin, dopamine 2b receptor (d2b), gonadotropin-releasing hormone (gnrh1), and β-subunit of follicle-stimulating hormone (fshβ) and luteinizing hormone (lhβ)—in the brain of the sapphire devil. During the reproductive season, mature females were divided into the early vitellogenesis (EV), late vitellogenesis (LV), and post-spawning (PS) stages; a day-low and night-high profile of aanat2 was observed during EV and LV but not during PS. There were nocturnal increases in gnrh1 during EV and LV as well as d2b during LV, suggesting that melatonin has a positive effect on the levels of gnrh1 and d2b transcripts in mature fish. When the brains of females in the non-breeding season were sampled at 4-h intervals, nocturnal increases in the levels of fshβ and lhβ transcripts were observed at 00:00 and 04:00, respectively. The immersion of immature fish in melatonin-containing seawater for 6 h resulted in the upregulation of fshβ and lhβ, as well as downregulation of d2b, in the brain. Additionally, in situ hybridization analysis showed that melatonin treatment lowered the signals of d2b transcripts in the ventral hypothalamus, rostral pars distalis, proximal pars distalis, and pars intermedia, suggesting that melatonin has a negative impact on the levels of d2b transcripts in the hypothalamus and pituitary of immature females; the opposite effect is likely concerning the levels of fshβ and lhβ transcripts in the pituitary. In conclusion, melatonin positively and negatively acted on the hypothalamus and pituitary in the sapphire devil; these opposite effects were related to differences in gonadal development status.

Spawning ecology of the Saint Paul's Gregory Stegastes sanctipauli, a damselfish endemic to the remote St. Peter and St. Paul's Archipelago.

We studied the spawning ecology of Stegastes sanctipauli, a damselfish endemic to the small and remote St. Peter and St. Paul's Archipelago (Brazil), aiming to determine the main correlates of reproductive success, as inferred from rates of egg losses along a spawning season. New clutches appeared mostly in the last quarter moon, when egg predation intensified. Predation by heterospecifics, particularly Halichoeres radiatus (Linnaeus, 1758), accounted for most egg losses, while filial cannibalism showed negligible influence. Predation pressure was highest for larger nests with higher initial density of eggs. Hatching of eggs occurred close to the new moon (i.e. ~5 days after spawning). Most nests occur in shallow reefs (<16 m depth), where main food resources for adults (turf algae) are concentrated, but abundance of egg predators, particularly H. radiatus, is also highest. This later result suggests that the spawning activity of S. sanctipauli is influenced by the trade-offs between food accessibility by adults and egg predation risk. The patterns recorded here are similar to those known for other tropical damselfish species and may reflect strategies for attenuating predation pressure over new fry and eggs.

Effect of short- and long-term melatonin treatments on the reproductive activity of the tropical damselfish Chrysiptera cyanea.

Photoperiod plays a role in controlling the initiation and termination of reproduction in fish. Melatonin is an internal transducer of environmental photoperiod and is involved in regulating reproduction. The present study aimed to examine how melatonin impacts the transcript levels of kisspeptin (kiss1 and kiss2), gonadotropin-releasing hormones (gnrh1), and the β-subunit of gonadotropins (fshβ and lhβ) in the brain of the sapphire devil, a tropical damselfish with long photoperiod preference. Feeding mature females with melatonin-containing pellets inhibited increases in the transcript levels of kiss1, gnrh1, and lhβ within 3 h. Continuous melatonin treatment for 1 week resulted in oocyte regression and downregulation of kiss2, gnrh1, fshβ, and lhβ. When the transcript levels of kiss1 and gnrh1 were measured at 4-h intervals in the brain of sapphire devil, a day-high/night-low fluctuation was observed. The hypothalamic-pituitary-gonadal (HPG) axis may be influenced by melatonin, exerting a negative effect at night because the transcript levels of aralkylamine N-acetyltransferase (aanat2) increased during the scotophase. The expression of aanat2 was higher under short-day than long-day conditions, suggesting that there is a seasonal change in melatonin levels at night. It was concluded that change in photoperiod becomes a key factor for controlling the hormone synthesis in the HPG axis through melatonin.

Plasticity to ocean warming is influenced by transgenerational, reproductive, and developmental exposure in a coral reef fish.

Global warming is expected to drive some ectothermic species beyond their thermal tolerance in upcoming decades. Phenotypic plasticity, via developmental or transgenerational acclimation, is a critical mechanism for compensation in the face of environmental change. Yet, it remains to be determined if the activation of beneficial phenotypes requires direct exposure throughout development, or if compensation can be obtained just through the experience of previous generations. In this study, we exposed three generations of a tropical damselfish to combinations of current‐day (Control) and projected future (+1.5°C) water temperatures. Acclimation was evaluated with phenotypic (oxygen consumption, hepatosomatic index, physical condition) and molecular (liver gene expression) measurements of third‐generation juveniles. Exposure of grandparents/parents to warm conditions improved the aerobic capacity of fish regardless of thermal conditions experienced afterwards, representing a true transgenerational effect. This coincided with patterns of gene expression related to inflammation and immunity seen in the third generation. Parental effects due to reproductive temperature significantly affected the physical condition and routine metabolic rate (oxygen consumption) of offspring, but had little impact on gene expression of the F3. Developmental temperature of juveniles, and whether they matched conditions during parental reproduction, had the largest influence on the liver transcriptional program. Using a combination of both phenotypic and molecular approaches, this study highlights how the conditions experienced by both previous and current generations can influence plasticity to global warming in upcoming decades.

Social familiarity improves fast-start escape performance in schooling fish

Using social groups (i.e. schools) of the tropical damselfish Chromis viridis, we test how familiarity through repeated social interactions influences fast-start responses, the primary defensive behaviour in a range of taxa, including fish, sharks, and larval amphibians. We focus on reactivity through response latency and kinematic performance (i.e. agility and propulsion) following a simulated predator attack, while distinguishing between first and subsequent responders (direct response to stimulation versus response triggered by integrated direct and social stimulation, respectively). In familiar schools, first and subsequent responders exhibit shorter latency than unfamiliar individuals, demonstrating that familiarity increases reactivity to direct and, potentially, social stimulation. Further, familiarity modulates kinematic performance in subsequent responders, demonstrated by increased agility and propulsion. These findings demonstrate that the benefits of social recognition and memory may enhance individual fitness through greater survival of predator attacks.

Effects of wave-driven water flow on the fast-start escape response of juvenile coral reef damselfishes.

Fish often evade predators with a fast-start escape response. Studies typically examine this behaviour in still water despite water motion being an inherent feature of aquatic ecosystems. In shallow habitats, waves create complex flows that likely influence escape performance, particularly in small fishes with low absolute swimming speeds relative to environmental flows. I examined how wave-driven water flow affects the behaviour and kinematics of escape responses in juveniles of three coral reef damselfishes (Pomacentridae) with different body morphologies. Tropical damselfishes have similar fin and body shapes during early development, with the exception of body depth, a trait deemed important for postural control and stability. Wave-driven flow increased response latency in two of the three species tested: fish with a fusiform body responded 2.9 times slower in wave-driven flow than in still water, whereas this difference was less pronounced in fish with an intermediate body depth (1.9 times slower response) and absent in fish with a laterally compressed body. The effect of wave-driven flow on swimming performance (cumulative escape distance and turning rate) was variable and depended on the timing and trajectory of escape responses in relation to the wave phase. Given intense predation pressure on juvenile coral reef fishes during settlement, interspecific differences in how wave-driven flow affects their ability to escape predators could influence the distribution and abundance of species across spatial and temporal scales.

Odd one in: Oddity within mixed‐species shoals does not affect shoal preference by vagrant tropical damselfish in the presence or absence of a predator

AbstractGrouping behaviour displayed by animals is usually attributed to predation and foraging‐related benefits. The mechanisms of predator protection and foraging efficiency are diverse and often produce conflicting drivers of grouping behaviour. One key conflict is that between group size and phenotypic oddity. Theoretically, individuals should choose the largest available group due to multiple mechanisms associated with “safety in numbers”. However, individuals should also choose the most phenotypically similar group members due to the “predator confusion effect”. This conflict is particularly important within the context of mixed‐species groups because, while their formation may facilitate large group size, phenotypic differences between species may be costly due to oddity. To investigate the interacting effects of shoal size, composition and predator presence on grouping decisions, choice experiments were conducted using displaced tropical damselfish, Abudefduf vaigiensis, settling in temperate south‐eastern Australia (termed vagrants) as a model species. Contrary to predictions, A. vaigiensis displayed no preference for single‐ over mixed‐species shoals, with or without a predator present. These results suggest that shoal composition may not be an important driver of shoal choice in this system. Further, A. vaigiensis showed no preference for larger mixed‐species shoals over smaller single‐species shoals. These outcomes are discussed within the context of climate change‐driven redistribution of A. vaigiensis in temperate south‐eastern Australia.

Food availability alters expression profiles of genes in relation to reproduction and nutrition in the females of tropical damselfish (Chrysiptera cyanea).

This study evaluated the effects of food availability on the transcript levels of genes related to reproduction and growth in the sapphire devil (Chrysiptera cyanea), a tropical damselfish. Nonbreeding fish were reared at high-food (HF) and low-food (LF) levels for 4 weeks under long-days. Vitellogenic oocytes could be observed in the ovaries of the HF group. The quantitative polymerase chain reaction analysis revealed that lhβ and cyp19b in the brains, vtg and igf1 in the livers and cyp19a in the ovaries of HF fish were significantly higher than that of LF fish, suggesting that estradiol-17β (E2) synthesis in the ovary and brain is activated when suitable permissive factors are available to fish. Food limitation lowered hepatic igf1 and dio2, suggesting that the TH-IGF1 signaling system functions in the liver, and that food availability altered hepatic deiodination activities related to intercellular levels of thyroid hormones. Hepatic dio2 significantly decreased when fish were immersed for 3 days in E2-containing seawater; this suggests that E2 impedes the conversion of T4 to T3 in the liver. Our study shows that igf1 was upregulated in accordance with HF-induced vitellogenesis but downregulated by E2 treatment, suggesting that igf1 is bidirectional and altered by maturational status. Once vitellogenesis begins under a suitable range of proximal factors, fish need to maintain their nutritional status because food availability is a permissive factor for their reproduction.

Molecular cloning of insulin-like growth factor 3 (igf3) and its expression in the tissues of a female damselfish, Chrysiptera cyanea, in relation to seasonal and food-manipulated reproduction

Food availability is a permissive determinant that drives gonadal activity in fish. The present study aimed to clarify the interactions between reproductive and nutritive statuses in the sapphire devil (Chrysiptera cyanea), a tropical damselfish with a long-day preference for reproduction. Insulin-like growth factor 3 (IGF3), a novel IGF that likely plays a role in gonadal maturation, was closely monitored in the sapphire devil. The cDNA of sapphire devil igf3 had an open reading frame of 443 base pairs (146 amino acid residues). Phylogenetic analyses revealed that sapphire devil IGF3 was clustered within the teleost IGF3 family. The transcript levels of sapphire devil igf3 increased in the brain, liver, and ovary of the fish during the late vitellogenic phase, suggesting that it plays a role in reproduction. Immersion of the fish in seawater containing estradiol-17β suppressed transcript levels of sapphire devil igf3 in the liver, but not in the brain, suggesting that intensive protein synthesis in relation to vitellogenesis negatively impacts somatic metabolism in this tissue. When fish were reared with high or low food under conditions of photoperiod (LD = 14:10) and temperature (at 25–28 °C) during the non-reproductive season, ovarian development was induced in high-food fish. Furthermore, prior to ovarian development in the high-food fish, the transcript levels of sapphire devil igf3 increased in the brain, liver, and ovary. These results indicated crosstalk between the reproductive and growth networks and suggested that a metabolic shift, from growth mode to reproductive mode, occurs in peripheral tissues when nutritive status is improved under suitable conditions of photoperiod and water temperature.

The mRNA expression patterns of kisspeptins, GnRHs, and gonadotropins in the brain and pituitary gland of a tropical damselfish, Chrysiptera cyanea, during the reproductive cycle.

The sapphire devil (Chrysiptera cyanea) is a tropical damselfish that undergoes active reproduction under long-day conditions. To elucidate the physiological regulation of the brain-pituitary-gonadal axis in female sapphire devil, we cloned and characterized the genes of two kisspeptins (kiss1 and kiss2), three gonadotropin-releasing hormones (gnrh1, gnrh2, gnrh3), and the β-subunit of two gonadotropins (fshβ and lhβ) and investigated the gene expression changes during ovarian development. Quantitative polymerase chain reaction analyses in various brain parts revealed high expression levels of kiss1, kiss2, and gnrh2 in the diencephalon; gnrh2 and gnrh3 in the telencephalon; and fshβ and lhβ in the pituitary. In situ hybridization (ISH) analyses revealed positive signals of kiss1 in the dorsal and ventral habenular nucleus and of kiss2 in the dorsal and ventral parts of the nucleus of the lateral recess. This analysis showed gnrh1 expression in the preoptic area (POA), suggesting that GnRH1 plays a stimulating role in the secretion of gonadotropins from the pituitary of the sapphire devil. High transcription levels of kiss1, kiss2, gnrh1, gnrh2, fshβ, and lhβ were observed in the brain during the late vitellogenic stage, suggesting their involvement in the physiological processes of vitellogenesis. Immersion of fish in estradiol-17β (E2)-containing seawater resulted in increased expression of kiss2 and gnrh1 in their brains. This study showed that kiss-expressing neurons in the diencephalon are influenced by E2, leading to upregulation of gnrh1 in the POA and of fshβ and lhβ in the pituitary during vitellogenesis.

The effects of water temperature on the juvenile performance of two tropical damselfishes expatriating to temperate reefs

Ocean warming associated with global climate change is already inducing geographic range shifts of marine species. Juvenile coral reef fishes transported into temperate latitudes (termed ‘vagrant’ fishes) can experience winter water temperatures below their normal thermal minimum. Such environmental extremes may increase energetic costs for such fishes, resulting in reduced performance, which may be the governing factor that limits the potential for poleward range expansion of such fishes. This study compared the juvenile physiological performance and behaviour of two congeneric tropical damselfishes which settle during austral summer months within temperate eastern Australia: Abudefduf vaigiensis have an extended southern range, and lower threshold survival temperature than the congeneric A. whitleyi. Physiological and behavioural performance parameters that may be affected by cooler temperature regimes at higher latitudes were measured in aquaria. Lower water temperature resulted in reduced growth rates, feeding rates, burst escape speed and metabolic rates of both species, with significantly reduced performance (up to six-fold reductions) for fishes reared at 18 °C relative to 22 °C and 26 °C. However, A. whitleyi exhibited lower growth rates than A. vaigiensis across all temperatures, and lower aerobic capacity at the lowest temperature (18 °C). This difference between species in growth and metabolic capacity suggests that the extended southern distribution and greater overwintering success of A. vaigiensis, in comparison to A. whitleyi is related to thermal performance parameters which are critical in maintaining individual health and survival. Our results support previous findings in the region that water temperature below 22 °C represents a critical physiological threshold for tropical Abudefduf species expatriating into temperate south-eastern Australia.

Expression profiles of types 2 and 3 iodothyronine deiodinase genes in relation to vitellogenesis in a tropical damselfish, Chrysiptera cyanea

Thyroid hormone (TH) is involved in regulating the reproduction of vertebrates. Its physiological action in the target tissues is due to the conversion of TH by iodothyronine deiodinases. In this study, we aimed to clone and characterize type 2 (sdDio2) and type 3 (sdDio3) of the sapphire devil Chrysiptera cyanea, a tropical damselfish that undergoes active reproduction under long-day conditions, and to study the involvement of THs in the ovarian development of this species. When the cDNAs of sdDio2 and sdDio3 were partially cloned, they had deduced amino acid sequences of lengths 271 and 267, respectively, both of which were characterized by one selenocysteine residue. Real-time quantitative PCR (qPCR) revealed that both genes are highly expressed in the whole brain, and sdDio2 and sdDio3 are highly transcribed in the liver and ovary, respectively. In situ hybridization analyses showed positive signals of sdDio2 and sdDio3 transcripts in the hypothalamic area of the brain. Little change in mRNA abundance of sdDio2 and sdDio3 in the brain was observed during the vitellogenic phases. It is assumed that simultaneous activation and inactivation of THs occur in this area because oral administration of triiodothyronine (T3), but not of thyroxine (T4), upregulated mRNA abundance of both genes in the brain. The transcript levels of sdDio2 in the liver and sdDio3 in the ovary increased as vitellogenesis progressed, suggesting that, through the metabolism of THs, sdDio2 and sdDio3 play a role in vitellogenin synthesis in the liver and yolk accumulation/E2 synthesis in the ovary. Taken together, these results suggest that iodothyronine deiodinases act as a driver for vitellogenesis in tropical damselfish by conversion of THs in certain peripheral tissues.

Latitudinal and Cross-Shelf Patterns of Size, Age, Growth, and Mortality of a Tropical Damselfish Acanthochromis polyacanthus on the Great Barrier Reef

Patterns of age and growth of a sedentary damsel fish Acanthochromis polyacanthus were tested over a latitudinal range of approximately 10 degrees (1200 km) on the Great Barrier Reef (GBR), Australia. Within latitudes, these patterns were also compared on reefs in distance strata (inner, mid, and outer) across a continental shelf that ranged in width from 52 to 128 km. Although variation in length-max (SLMAX), growth, age-max (AMAX), and the von Bertalanffy metrics of Linf and K were found within and among latitudes, the greatest variation in some demographic characteristics was found among distance strata across the shelf regardless of latitude. Fish were always relatively smaller at inner shelf reefs and grew more slowly when compared to mid and outer shelf reefs; this was true regardless of the color morph of fish. The oldest fish collected was 11 years old, and there was no consistent variation in age-max among distances from shore. On outer reefs, there was a negative linear relationship with age-max and latitude. This “tropical gradient” of age only explained 34% of the variation; furthermore, this was not found when only the oldest group of fish was considered (top 10%). Fish only reached an age-max of six years on the southernmost reefs. There was a trend for a smaller Linf with latitude but it was not significant and Linf did not vary predictably with water temperature. The sampling of marine protected areas (MPAs) and fished zones did not confound the resultant patterns in that fish were not consistently larger or older in MPAs or fished zones. Instantaneous mortality rates were 0.245–0.685; they were highest at inner reefs and also showed no consistent MPA-related patterns. Our study suggested that the mid and outer shelf waters of the GBR appeared best suited for growth of A. polyacanthus. In conclusion, the position on continental shelves dominated other geographical patterns and needs to be considered in spatial models of growth. We suggest that local environmental conditions such as turbidity and the quality and quantity of plankton likely have a strong influence on distance across the shelf-based demographic patterns of planktivores.

Changes in mRNA abundance of insulin-like growth factors in the brain and liver of a tropical damselfish, Chrysiptera cyanea, in relation to seasonal and food-manipulated reproduction

Food availability can become a factor driving the reproductive activity of tropical fish, particularly when primary production within their habitats fluctuates with tropical monsoons. The present study examined the involvement of insulin-like growth factors (IGF) in controlling the reproduction of the sapphire devil Chrysiptera cyanea, a reef-associated damselfish that is capable of manipulating its reproductive activity based on food availability. We cloned and characterized the cDNAs of igf1 and igf2 and determined their transcript levels in relation to seasonal and food-manipulated reproduction. The partial cDNAs of sapphire devil igf1 and igf2 had open reading frames (ORFs) composed of 600 bp (155 amino acid residue) and 636 bp (211 aa), respectively. Phylogenetic analyses revealed that IGF1 and IGF2 of the sapphire devil were clustered into those of teleosts. The gonadosomatic index increased from March to June. Vitellogenic oocytes and ovulatory follicles were observed in ovaries from May to June, which suggests that the spawning season lasts for at least 2 months. The hepatosomatic index, but not the condition factor, increased in March and June. The transcript levels of igf1 in the brain, but not in the liver, increased in April, June (vitellogenesis) and July (post vitellogenesis). Ovarian activity during the spawning season was maintained by high food supply (HH) for 30 days, although it was suppressed in the food-restriction treatment (LL) and restored in the re-feeding treatment (LH). The transcript levels of igfs in the brain, but not in the liver, in LH were lower than those in HH and LL. Moreover, immersing fish in seawater containing estradiol-17β suppressed transcript levels of igfs in the liver, but not in the brain. We conclude that reproductive activity during the spawning season is influenced by nutritive conditions and that crosstalk exists between the reproductive and growth network in the neural and peripheral tissues, thus controlling the reproductive activity of this species.

Role of water flow regime in the swimming behaviour and escape performance of a schooling fish

ABSTRACTAnimals are exposed to variable and rapidly changing environmental flow conditions, such as wind in terrestrial habitats and currents in aquatic systems. For fishes, previous work suggests that individuals exhibit flow-induced changes in aerobic swimming performance. Yet, no one has examined whether similar plasticity is found in fast-start escape responses, which are modulated by anaerobic swimming performance, sensory stimuli and neural control. In this study, we used fish from wild schools of the tropical damselfish Chromis viridis from shallow reefs surrounding Lizard Island in the Great Barrier Reef, Australia. The flow regime at each site was measured to ascertain differences in mean water flow speed and its temporal variability. Swimming and escape behaviour in fish schools were video-recorded in a laminar-flow swim tunnel. Though each school's swimming behaviour (i.e. alignment and cohesion) was not associated with local flow conditions, traits linked with fast-start performance (particularly turning rate and the distance travelled with the response) were significantly greater in individuals from high-flow habitats. This stronger performance may occur due to a number of mechanisms, such as an in situ training effect or greater selection pressure for faster performance phenotypes in areas with high flow speed.This article has an associated First Person interview with the first author of the paper.

Reproductive synchrony in a temperate damselfish, Chromis limbata

Synchronous reproduction has been reported in many tropical damselfishes, and it appears that temperature is the main driver of synchrony at these latitudes. However, reproductive synchrony and its relation to temperature is less well understood in temperate damselfish. The endemic Azores chromis (Chromis limbata) was chosen as a study species to address this topic. First, an ethogram of the reproductive behaviour and embryo development of the Azores chromis is provided. Then, are investigated (1) the reproductive dynamics at the colonial and inter-colonial levels, (2) how these are affected by temperature, and (3) the relation between reproductive dynamics and the social organization of temperate damselfish. In the Azores chromis, reproduction was cyclic with a high periodicity of 7.2 ± 0.63 days on average. Embryo development was synchronous within colonies towards the beginning and the end of incubation, but not at intermediate stages of development. Colonies that were closer were more synchronized than those located further apart, despite contrasting temperature and depth profiles. Embryo size differences were also greater between colonies that were further apart, and embryos tended to grow larger in warmer water. A literature review revealed that reproductive synchrony was common in colonial breeding damselfish species. Although these results suggest that within the breeding season, the timing and length of reproductive cycles cannot be explained by temperature alone, the observed changes in embryo size raise concern about the effects of changing oceanic conditions on this species.

Record high damselfish recruitment at Rottnest Island, Western Australia, and the potential for climate-induced range extension

Three-decades of observations of tropical fish recruitment on the south coast of Rottnest Island, Western Australia (WA), have indicated that settlement of two tropical damselfish (Abudefduf sexfasciatus and A. vaigiensis) peaks each autumn with the seasonal strengthening of the Leeuwin Current (LC). Historically these fish have not bred at Rottnest Island or at other adjacent coastal locations although an active breeding population exists at the Houtman Abrolhos Islands some 330 km to the north. Record levels of recruitment in early 2011 followed extremely strong southward advection in the LC accompanied by unprecedented high water temperatures associated with a marine heat wave. Settlement numbers the following year were almost as high, again associated with a very strong LC and high water temperatures, while 2013 saw lower but still above average recruitment. Against a background of gradual ocean warming along the WA coast, one of the world’s 30 hotspots for increasing ocean temperature, the potential for these species to establish a breeding population at Rottnest Island is explored by comparing the water temperatures during the presumed spawning period at the Abrolhos Islands with those at Rottnest Island together with winter temperatures and the abundance of what are believed to be mature Abudefduf successfully over-wintering at Rottnest Island. “The results indicate that establishment of a breeding population at Rottnest Island does not appear to be limited by water temperatures, and raises the question as to why a breeding population does not already exist as the settlement habitat appears very similar to that at the Abrolhos Islands.

Molecular cloning of kisspeptin receptor genes (gpr54-1 and gpr54-2) and their expression profiles in the brain of a tropical damselfish during different gonadal stages

The kisspeptin receptor (GPR54) mediates neuroendocrine control of kisspeptin in the brain and acts as a gateway for a pulsatile release of hypothalamic gonadotropin-releasing hormone. This study aimed to clone two GPR54 genes (gpr54-1 and gpr54-2) from the brain of the sapphire devil Chrysiptera cyanea, a tropical damselfish, and to study their involvement in reproduction. The partial sequences of the sapphire devil gpr54-1 cDNA (1059bp) and gpr54-2 cDNA (1098bp) each had an open reading frame encoding a protein of 353 and 366 amino acids, respectively, both of which had structural features of a G-protein-coupled receptor. The expression of gpr54-1 mRNA was observed in the diencephalon and telencephalon, and gpr54-2 mRNA was found in the optic tectum of sapphire devil. When gpr54-1 and gpr54-2 mRNA levels were examined in the brain of sapphire devil by real-time quantitative polymerase chain reaction (qPCR), they were found to increase during late vitellogenesis and post-spawning. Treatment of fish with estradiol-17β (Ε2) resulted in an increase in gpr54-1 and gpr54-2 expression in the brain of sapphire devil. Thus, kisspeptin receptors likely mediate the activity of kisspeptin in the brain and are involved in controlling reproductive events in a tropical damselfish.

Protogyny in a tropical damselfish: females queue for future benefit.

Membership of the group is a balance between the benefits associated with group living and the cost of socially constrained growth and breeding opportunities, but the costs and benefits are seldom examined. The goal of the present study was to explore the trade-offs associated with group living for a sex-changing, potentially protogynous coral reef fish, the Ambon damselfish, Pomacentrus amboinensis. Extensive sampling showed that the species exhibits resource defence polygyny, where dominant males guard a nest site that is visited by females. P. amboinensis have a longevity of about 6.5 years on the northern Great Barrier Reef. While the species can change sex consistent with being a protogynous hermaphrodite, it is unclear the extent to which the species uses this capability. Social groups are comprised of one reproductive male, 1–7 females and a number of juveniles. Females live in a linear dominance hierarchy, with the male being more aggressive to the beta-female than the alpha-female, who exhibits lower levels of ovarian cortisol. Surveys and a tagging study indicated that groups were stable for at least three months. A passive integrated transponder tag study showed that males spawn with females from their own group, but also females from neighbouring groups. In situ behavioural observations found that alpha-females have priority of access to the nest site that the male guarded, and access to higher quality foraging areas. Male removal studies suggest that the alpha-females can change sex to take over from the male when the position becomes available. Examination of otolith microstructure showed that those individuals which change sex to males have different embryonic characteristics at hatching, suggesting that success may involve a component that is parentally endowed. The relative importance of parental effects and social organisation in affecting the importance of female queuing is yet to be studied, but will likely depend on the strength of social control by the dominant members of the group.