Future thermal regimes for epaulette sharks (Hemiscyllium ocellatum): growth and metabolic performance cease to be optimal

Climate change is affecting thermal regimes globally, and organisms relying on their environment to regulate biological processes face unknown consequences. In ectotherms, temperature affects development rates, body condition, and performance. Embryonic stages may be the most vulnerable life history stages, especially for oviparous species already living at the warm edge of their distribution, as embryos cannot relocate during this developmental window. We reared 27 epaulette shark (Hemiscyllium ocellatum) embryos under average summer conditions (27 °C) or temperatures predicted for the middle and end of the twenty-first century with climate change (i.e., 29 and 31 °C) and tracked growth, development, and metabolic costs both in ovo and upon hatch. Rearing sharks at 31 °C impacted embryonic growth, yolk consumption, and metabolic rates. Upon hatch, 31 °C-reared sharks weighed significantly less than their 27 °C-reared counterparts and exhibited reduced metabolic performance. Many important growth and development traits in this species may peak after 27 °C and start to become negatively impacted nearing 31 °C. We hypothesize that 31 °C approximates the pejus temperature (i.e., temperatures at which performance of a trait begin to decline) for this species, which is alarming, given that this temperature range is well within ocean warming scenarios predicted for this species’ distribution over the next century.

Morphologies description of Halmahera epaulette shark endemic species (Hemiscyllium halmahera, Allen & Erdmann, 2013) in North Maluku Sea

Halmahera Epaulette Shark (Hemiscyllium halmahera) is an endemic fish in the North Maluku sea. This species was first discovered in two spots of Halmahera waters namely Ternate and Bacan in 2013. Halmahera Epaulette Shark research was continue in Weda and Kao Bay in 2016, 2017 and 2018. Those previous studies, however, did not reveal the morphological description of this species in the other part of the Halmahera Islands. This research was made to enhance the information about this species from the other part of Halmahera waters with a purpose to describe the morphology of Halmahera epaulette shark. The study was carried out in remote areas of Loleo, Tidore, Maitara, Mare, and Lelei Island in 2018. Photos of fish were documented, some meristic and morphometric characters and body weigt were measured. Halmahera epaulette shark has many local names. Observation results showed that many dark brown spots with different patterns and shapes were present with 0.5-1.2 cm in diameter. The total and standard lengths were 40-63 cm and 35-55 cm, respectively. Head length and head width ranged from 7-12 cm and 3-6 cm, respectively. The head height ranged from 9-10 cm. The body circumference of fish ranged between 11-24 cm. Pectoral fins length ranged from 4-6 cm. The dorsal fin length ranged from 5-6 cm. The lower tail length ranged from 4-6 cm. The upper tail length ranged from 4-6 cm. Fish mouth type is subterminal with pointed teeth.

A new subfamily for a clade of opecoelids (Trematoda: Digenea) exploiting marine fishes as second-intermediate hosts, with the first report of opecoelid metacercariae from an elasmobranch

Metacercariae of trematodes belonging to the family Opecoelidae were collected from small fishes of the Great Barrier Reef: a blenniid, two gobiids, two labrids, three pomacentrids, a monacanthid, an ostraciid and the epaulette shark, Hemiscyllium ocellatum. Sequences of the second internal transcribed spacer region (ITS2) of ribosomal DNA were generated from these metacercariae in an attempt to match them with adult worms. Three species of Allopodocotyle (Allopodocotyle epinepheli, Allopodocotyle heronensis and an unidentified species), two unidentified species of Hamacreadium and Pacificreadium serrani were detected. Among the Opecoelidae, these species all resolve to a single, phylogenetically and somewhat morphologically distinct clade. Species of this clade are the only known marine opecoelids to exploit fishes as second-intermediate hosts. The clade is proposed to warrant a new subfamily, the Hamacreadiinae subfam. nov. It includes Allopodocotyle, Bentholebouria, Cainocreadium, Choanotrema, Hamacreadium, Pacificreadium, Paraplagioporus, Pedunculacetabulum and Podocotyloides.

Foraging behaviour of the epaulette shark Hemiscyllium ocellatum is not affected by elevated CO2

Increased oceanic uptake of atmospheric carbon dioxide (CO2) is a threat to marine organisms and ecosystems. Among the most dramatic consequences predicted to date are behavioural impairments in marine fish which appear to be caused by the interference of elevated CO2 with a key neurotransmitter receptor in the brain. In this study, we tested the effects of elevated CO2 on the foraging and shelter-seeking behaviours of the reef-dwelling epaulette shark, Hemiscyllium ocellatum. Juvenile sharks were exposed for 30 d to control CO2 (400 µatm) and two elevated CO2 treatments (615 and 910 µatm), consistent with medium- and high-end projections for ocean pCO2 by 2100. Contrary to the effects observed in teleosts and in some other sharks, behaviour of the epaulette shark was unaffected by elevated CO2. A potential explanation is the remarkable adaptation of H. ocellatum to low environmental oxygen conditions (hypoxia) and diel fluctuations in CO2 encountered in their shallow reef habitat. This ability translates into behavioural tolerance of near-future ocean acidification, suggesting that behavioural tolerance and subsequent adaptation to projected future CO2 levels might be possible in some other fish, if adaptation can keep pace with the rate of rising CO2 levels.

Transcriptional responses to hypoxia are enhanced by recurrent hypoxia (hypoxic preconditioning) in the epaulette shark

All animals require molecular oxygen for aerobic energy production, and oxygen availability has played a particularly important role in the evolution of aquatic animals. This study investigates how previous exposure to hypoxia (preconditioning) primes protective transcriptional responses in a hypoxia-tolerant vertebrate species, the epaulette shark ( Hemiscyllium ocellatum). The epaulette shark is a basal cartilaginous fish that in its natural environment experiences cyclic hypoxic periods. We evaluated whether the transcription of a set of crucial prosurvival genes is affected differently by a single short-term (2 h) exposure to sublethal hypoxia compared with eight such successive hypoxia exposures (hypoxia preconditioning). We discovered that hypoxia preconditioning amplifies transcriptional responses compared with animals that experienced a single hypoxic bout. In the heart we observed that hypoxic preconditioning, but not a single hypoxic exposure, resulted in higher transcript levels of genes that regulate oxygen and energy homeostasis, including those of hypoxia-inducible factor-1 alpha, adenosine signaling pathway components, and genes affecting circulation [prostaglandin synthetase 2 ( cox-2) and natriuretic peptide C]. This suggests that in a single short-term hypoxic bout, the responses to low oxygen are regulated at the level of pre-existing proteins or translational and posttranslational machinery, whereas transcriptional responses are induced in experiments that parallel the natural environmental cycles of oxygen availability. These findings have general implications for understanding how vertebrates regulate protective gene expression upon physiological stress.