Is post-feeding thermotaxis advantageous in elasmobranch fishes? (original) (raw)
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Effect of rapid temperature change on resting routine metabolic rates of two benthic elasmobranchs
Fish Physiology and Biochemistry
In this study, flow-through respirometry was used to test the effect of acute temperature change on resting routine metabolic rates of two benthic elasmobranchs, Atlantic stingrays, Dasyatis sabina (n = 7) and whitespotted bamboo sharks, Chiloscyllium plagiosum (n = 7) kept under fluctuating temperature regime of 24–27 and 23–25°C, respectively. Atlantic stingrays and whitespotted bamboo sharks showed a temperature sensitivity (Q10) of 2.10 (21–31°C) and 2.08 (20–28°C), respectively. Not surprisingly, oxygen consumption (MO2) increased in both species as temperature was raised. Acute increases in oxygen uptake may be useful during activities such as foraging, and some elasmobranchs may alter physiological processes by taking advantage of thermal variability in the environment. However, further investigation of different physiological processes is needed to better understand how temperature variation may affect behavioural choices of fishes.
How the liver contributes to stomach warming in the endothermic white sharkCarcharodon carcharias
BackgroundWhite sharks and other lamnids are able to elevate their stomach temperature. The ability to heat large amounts of food to the recorded levels of up to 17°C above the ambient water temperature can’t be explained only by the heat generated by catabolism and the endothermic adaptions of the suprahepatic rete. This rete has two shunts that regulates the volume of blood flowing from the liver to the sinus venosus, thereby providing a temperature control mechanism for the GIT. The liver’s function in this temperature regulation is unknown. White shark stomach volume is well above 135 l in sub-adults to accommodate large prey items, including marine mammals. The simultaneous ingestion of large volumes of cold water during feeding will result in marked cooling of the stomach. Our study investigated the role of the liver in relation to warming the gastro-intestinal tract and the retention of elevated core temperatures.Materials and methodsThe liver morphology and its position rela...
Does food quality influence thermoregulatory behavior in the intertidal fish Girella laevifrons?
Journal of thermal biology, 2003
Algal and invertebrate species are less abundant towards higher zones of the intertidal, where the greatest variations in physical environmental conditions occur. Mobile predators such as fishes that inhabit high intertidal rockpools are thus exposed to wide variations in physical conditions and to a low abundance and quality of food. We used an aquarium with a temperature gradient in the laboratory to assesed whether dietary quality differences modify temperature preferences of Girella laevifrons, one of the most abundant transitory fishes inhabiting rocky shores along the coast of Chile. Our results indicate that food quality clearly modifies temperature preferences in this species. Animals fed on high quality bivalves selected intermediate temperatures (16-18 C) while those fed on lower quality algae selected lower temperatures (10-12 C). Control fish not subjected to the temperature gradient did not select portions of the aquarium differentially. The thermal selectivity of G. laevifrons in relation to the optimization of digestive processes and mechanisms of energy conservation are discussed. r
Newton et al 2015 Mako shark digestive enzyme visceral endothermy
Lamnid sharks are regionally endothermic fishes that maintain visceral temperatures elevated above the ambient water temperature. Visceral en-dothermy is thought to increase rates of digestion and food processing and allow thermal niche expansion. We tested the hypothesis that, at in vivo temperatures, the endothermic shortfin mako shark, Isurus oxy-rinchus, has higher specific activities of three digestive enzymes—gastric pepsin and pancreatic trypsin and lipase—than the thresher shark, Alopias vulpinus, and the blue shark, Prionace glauca, neither of which can maintain elevated visceral temperatures. Ho-mogenized stomach or pancreas tissue obtained from sharks collected by pelagic longline was incubated at both 15 and 25 °C, at saturating substrate concentrations, to quantify tissue enzymatic activity. The mako had significantly higher enzyme activities at 25 °C than did the thresher and blue sharks at 15 °C. This difference was not a simple temperature effect, because at 25 °C the mako had higher trypsin activity than the blue shark and higher activities for all enzymes than the thresher shark. We also hypothesized that the thermal coefficient, or Q 10 value, would be higher for the mako shark than for the thresher and blue sharks because of its more stable visceral temperature. However, the mako and thresher sharks had similar Q 10 values for all enzymes, perhaps because of their closer phylogenetic relationship. The higher in vivo digestive enzyme activities in the mako shark should result in higher rates of food processing and may represent a selective advantage of regional visceral endothermy.
Variations in gastric acid secretion during periods of fasting between two species of shark
Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 2005
Vertebrates differ in their regulation of gastric acid secretion during periods of fasting, yet it is unknown why these differences occur. Elasmobranch fishes are the earliest known vertebrates to develop an acid secreting stomach and as such may make a good comparative model for determining the causative factors behind these differences. We measured gastric pH and temperature continuously during periods of fasting in captive free-swimming nurse sharks (Ginglymostoma cirratum) using autonomous pH/temperature data-loggers. All nurse sharks secreted strong gastric acids (minimum pH 0.4) after feeding; however, for most of the sharks, pH increased to 8.2-8.7, 2-3 days after feeding. Half of the sharks also exhibited periodic oscillations in pH when the stomach was empty that ranged from 1.1 to 8.7 (acid secretion ceased for 11.3 T 4.3 h day À 1). This is in contrast to the gastric pH changes observed from leopard sharks (Triakis semifasciata) in a previous study, where the stomach remains acidic during fasting. The leopard shark is a relatively active, more frequently feeding predator, and continuous acid secretion may increase digestive efficiency. In contrast, the nurse shark is less active and is thought to feed less frequently. Periodic cessation of acid secretion may be an energy conserving mechanism used by animals that feed infrequently and experience extended periods of fasting.
Proceedings. Biological sciences / The Royal Society, 2014
Temperature acclimation may offset the increased energy expenditure (standard metabolic rate, SMR) and reduced scope for activity (aerobic scope, AS) predicted to occur with local and global warming in fishes and other ectotherms. Yet, the time course and mechanisms of this process is little understood. Acclimation dynamics of SMR, maximum metabolic rate, AS and the specific dynamic action of feeding (SDA) were determined in shorthorn sculpin (Myoxocephalus scorpius) after transfer from 10°C to 16°C. SMR increased in the first week by 82% reducing AS to 55% of initial values, while peak postprandial metabolism was initially greater. This meant that the estimated AS during peak SDA approached zero, constraining digestion and leaving little room for additional aerobic processes. After eight weeks at 16°C, SMR was restored, while AS and the estimated AS during peak SDA recovered partly. Collectively, this demonstrated a considerable capacity for metabolic thermal compensation, which sh...
Journal of Experimental Biology, 2014
Climate warming is predicted to negatively impact fish populations through impairment of oxygen transport systems when temperatures exceed those which are optimal for aerobic scope (AS). This concept of oxygen-and capacity-limited thermal tolerance (OCLTT) is rapidly gaining popularity within climate change research and has been applied to several fish species. Here, we evaluated the relevance of aerobic performance of juvenile barramundi (Lates calcarifer) in the context of thermal preference and tolerance by (1) measuring standard and maximum metabolic rates (SMR and MMR, respectively) and AS of fish acclimated to 29°C and acutely exposed to temperatures from 23 to 38°C, (2) allowing the fish to behaviourally select a preferred temperature between 29 and 38°C, and quantifying alterations to AS after 5 weeks of acclimation to 29 and 38°C. SMR and MMR both increased continuously with temperature in acutely exposed fish, but the increase was greater for MMR such that AS was highest at 38°C, a temperature approaching the upper lethal limit (40-41°C). Despite 38°C eliciting maximum AS, when given the opportunity the fish selected a median temperature of 31.7±0.5°C and spent only 10±3% of their time at temperatures >36°C. Following acclimation to 38°C, AS measured at 38°C was decreased to the same level as 29°C-acclimated fish measured at 29°C, suggesting that AS may be dynamically modulated independent of temperature to accommodate the requirements of daily life. Together, these results reveal limited power of the OCLTT hypothesis in predicting optimal temperatures and effects of climate warming on juvenile barramundi.
Marine Ecology, 2016
Digestive metabolism is considered key to resilience of fish populations as it determines energy and nutrient availability for growth and survival. In cleaner fishes, digestion performance also influences the amount and the rate at which parasites can be removed from cooperating fishes, called hosts. Therefore, understanding the effect of temperature on digestive metabolic scope (i.e. the energy allocated to digestive processes) is crucial to predicting responses of fish communities to ocean warming. Body size can affect many physiologic processes and is thought to decrease with increasing temperature; therefore, we examined the effect of body mass and warming on digestive metabolic scopes in two sister species of cleaner gobies of the genus Elacatinus that reach different adult sizes. The dwarf-size Elacatinus lobeli increased digestive metabolic rates and scope while the larger Elacatinus oceanops decreased digestive metabolic scope with warming. Intra-specifically, larger E. lobeli also showed a decreased scope when compared to smaller individuals. Results from this study suggest that perhaps smaller fishes may have a digestive and metabolic advantage at higher temperatures and may be more resilient under warming temperatures.
The Biological Bulletin
Spiny dogfish (Squalus acanthias) and smoothhound (Mustelus canis) sharks in the northwest Atlantic undergo seasonal migrations driven by changes in water temperature. However, the recognized thermal habitats of these regional populations are poorly described. Here, we report the thermal range, catch frequency with bottom temperature, and catch frequency with time of year for both shark species in Narragansett Bay, Rhode Island. Additionally, we describe levels of two thermal stress response indicators, heat-shock protein 70 and trimethylamine N-oxide, with an experimental increase in water temperature from 15 7C to 21 7C. Our results show that S. acanthias can be found in this region year-round and co-occurs with M. canis from June to November. Further, adult S. acanthias routinely inhabits colder waters than M. canis (highest catch frequencies at bottom temperatures of 10 7C and 21 7C, respectively), but both exhibit similar upper thermal ranges in this region (bottom temperatures of 22-23 7C). Additionally, acute exposure to a 6 7C increase in water temperature for 72 hours leads to a nearly threefold increase in heat-shock protein 70 levels in S. acanthias but not M. canis. Therefore, these species display differences in their thermal tolerance and stress response with experimental exposure to 21 7C, a common summer temperature in Narragansett Bay. Further, in temperature-stressed S. acanthias there is no accumulation of trimethylamine N-oxide. At the whole-organism level, elasmobranchs' trimethylamine N-oxide regulatory capacity may be limited by other factors. Alternatively, elasmobranchs may not rely on trimethylamine N-oxide as a primary thermal protective mechanism under the conditions tested. Findings from this study are in contrast with previous research conducted with elasmobranch cells in vitro that showed accumulation of trimethylamine N-oxide after thermal stress and subsequent suppression of the heat-shock protein 70 response.