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Post-translational modification with O-linked β-N-acetylglucosamine (O-GlcNAc) occurs selectively on serine and/or threonine residues of cytoplasmic and nuclear proteins, and dynamically regulates their molecular functions. Since conventional strategies to evaluate the O-GlcNAcylation level of a specific protein require time-consuming steps, the development of a rapid and easy method for the detection and quantification of an O-GlcNAcylated protein has been a challenging issue. Here, we describe a novel method in which O-GlcNAcylated and non-O-GlcNAcylated forms of proteins are separated by lectin affinity gel electrophoresis using wheat germ agglutinin (WGA), which primarily binds to N-acetylglucosamine residues. Electrophoresis of cell lysates through a gel containing copolymerized WGA selectively induced retardation of the mobility of O-GlcNAcylated proteins, thereby allowing the simultaneous visualization of both the O-GlcNAcylated and the unmodified forms of proteins. This method is therefore useful for the quantitative detection of O-GlcNAcylated proteins.

Tunas can elevate their red (slow-twitch, oxidative) skeletal muscle, visceral and cranial temperatures significantly above the ambient water temperature (Ta) with the aid of specialized blood vessels (retia mirabilia) that conserve metabolic heat. The ontogeny of this phenomenon, known as regional endothermy, was studied in young [18.5–62.5 cm fork length (FL), 71–5350 g body mass, 2–16 months of age] Pacific bluefin tuna (Thunnus orientalis). Maximal red muscle, visceral and cranial temperatures were measured in parallel with measuring red muscle mass and the size of the red muscle and visceral retia. The maximal thermal excess (maximal tissue temperature – Ta) increased from 1.1 ± 0.3 °C (mean ± SD) to 11.1 ± 3.4 °C in the red muscle, from 0.6 ± 0.3 °C to 3.5 ± 1.4 °C in the viscera and from 0.5 ± 0.4 °C to 2.0 ± 0.6 °C in the cranium in the smallest individuals compared with the largest. Thus, red muscle endothermy was well developed, but visceral and cranial endothermy were still developing, in the largest individuals studied. The scaling coefficients, relative to body mass, for total red muscle mass (0.90 ± 0.03, mean ± SE), red muscle rete (RMR) length (0.84 ± 0.06), maximum number of RMR blood vessel rows (0.43 ± 0.04) and visceral rete cross-sectional area (0.90 ± 0.08), indicated negative allometry for total red muscle mass (< 1.0) but positive allometry for the length of the red muscle retia (> 0.33) and the area of the visceral rete (> 0.67).

This study aimed to clarify the mechanisms contributing to ontogenetic differences in red locomotor muscle metabolic heat production in regionally endothermic tunas. To address this, the scaling of citrate synthase (CS), cytochrome c oxidase (COX) and pyruvate kinase (PK), enzymes involved in cellular respiration, in the red and white locomotor muscle of young (~ 2 to ~ 16 months of age) Pacific bluefin tuna (Thunnus orientalis) during the ontogeny of red muscle endothermy was investigated. On a mass-specific basis (units g−1 muscle tissue), CS activity scaled negatively with body mass with scaling coefficients of −0.12 for red muscle and −0.21 for white muscle, whereas COX activity did not scale in either muscle type and PK activity scaled positively in white muscle, with a scaling coefficient of 0.09, but did not scale in red muscle. Thus, proxies for mass-specific metabolic heat production potential from cellular respiration either decreased or remained constant in the red muscle during the ontogeny of red muscle endothermy. In contrast, total red muscle mass and total CS and COX activities all scaled positively with body mass, with scaling coefficients of 0.90, 0.78 and 0.92, respectively, and each of these correlated positively with the magnitude of the red muscle thermal excess. Thus, increasing total, but not mass-specific, metabolic heat production capacity contributed to the increasing red muscle thermal excess with increasing body size in juvenile T. orientalis. Additionally, transcript abundance was a poor predictor of enzyme activity. Thus, transcriptional regulation played a limited role in determining the enzymes’ scaling relationships.

There is a potential trade-off between grouping and the optimizing of the energetic efficiency of individual locomotion. Although intermittent locomotion, e.g. glide and upward swimming (GAU), can reduce the cost of locomotion at the individual level, the link between the optimization of individual intermittent locomotion and the behavioural synchronization in a group, especially among members with different sizes, is unknown. Here, we continuously monitored the schooling behaviour of a negatively buoyant fish, Pacific bluefin tuna (N = 10; 21.0 ∼ 24.5 cm), for 24 h in an open-sea net cage using accelerometry. All the fish repeated GAU during the recording periods. Although the GAU synchrony was maintained at high levels (overall mean = 0.62 for the cross-correlation coefficient of the GAU timings), larger fish glided for a longer duration per glide and more frequently than smaller fish. Similar-sized pairs showed significantly higher GAU synchrony than differently sized pairs. Our accelerometry results and the simulation based on hydrodynamic theory indicated that the advantage of intermittent locomotion in energy savings may not be fully optimized for smaller animals in a group when faced with the maintenance of group cohesion, suggesting that size assortative shoaling would be advantageous.

Although archival tags have been deployed in Thunnus since the early 1990s, few studies have placed such loggers on the small-size growth stage. In this study, Pacific bluefin tuna (PBT, Thunnus orientalis ) 20–26.5 cm in fork length (FL) were fitted with archival tags and released off the southern coastal area of Japan from July to August in 2012, 2013, and 2014. Time-series data on swimming depth, ambient water temperature, and peritoneal cavity temperatures collected at 30-s intervals during 78–144 days were analyzed in 11 age-0 PBT. In August, the age-0 PBT spent 69.5 to 83.4% of their time within the mixed layer at mean temperatures between 27.6 and 28.3 °C, while previous studies reported that PBT with FL > 50 cm in the East China Sea are found most often in zones with temperatures between 14 and 19 °C. The thermal difference between the peritoneal cavity and ambient temperature was less than 1 °C for age-0 PBT in August, indicating that they were not in danger of overheating. The mean daytime swimming depths of age-0 PBT were significantly and positively correlated with the depth of the thermocline, especially from August to October. By focusing their swimming depths around the thermocline, the age-0 PBT potentially maximize the probability of encountering prey. There was a significant correlation between the mean nighttime depth and lunar illumination. The change in vertical distribution with the lunar cycle during nighttime is likely a form of predator avoidance.

Environmental changes influence foraging behavior for most animals. Dolphinfish, Coryphaena hippurus , are epipelagic predators and have a cosmopolitan tropical to warm-temperate (>20°C) distribution. We simultaneously obtained the ambient temperature and the foraging behavior (i.e., swimming speed, depth and tailbeat acceleration) of dolphinfish, using an acceleration data-logger in May, September, October, November 2007, June 2008, May and July 2010 for 8 individuals. Although the dolphinfish spent a mean ± standard deviation of 43.4 ± 27.7% of their time at the surface (0–5 m), dive excursions from the surface (DES) were observed in all individuals and maximum DES depths ranged from 50.1 to 95.4 m. DES events resulted dives below the thermocline for these dolphinfish, and there was a significantly positive relationship between the isothermal layer depth (ILD) and DES depth. Our results demonstrate that dolphinfish avoided the rapid thermal change beyond the thermocline, and their prey is most likely found in the upper layers of the thermocline. Gliding behavior during the DES phase was also observed and dolphinfish gradually descended to deeper waters with gliding. The gliding time was longer when the ILD was deeper, and fish tended to dive deeper. We suggest that dolphinfish adopt gliding behavior to search a broader range of depths for prey, while minimizing energy use.

We measured white muscle isotopic compositions and aspect ratios (ARs) of caudal fins in juvenile Pacific bluefin tuna Thunnus orientalis (PBT) to examine ontogenetic dietary shifts and swimming ability. ARs averaged 3.9 in fish with fork length (FL) <15 cm, 4.6 in fish with FL of 30–35 cm, and 6.7 in adult fish with FL >200 cm. Mean isotope values of carbon and nitrogen in white muscle increased from −18.3 to −18.0‰ and from +7.2 to 8.9‰ in ~20 cm fish to −16.5‰ and +12.3‰ in 30–35 cm fish, respectively, with a shift at 25 cm FL. This shift was much earlier than that reported for yellowfin tuna T. albacares (40–50 cm FL). Our results suggest that, after moving to Japanese coastal areas and reaching a FL of 25 cm, PBT rapidly develop swimming abilities by achieving endothermy and switching from a diet of small squid and zooplankton to a diet based on fish prey items that have greater body mass with higher calorific content and swimming ability. This may give them a selective advantage and allow high energetic expenditure.

Homing behaviour—a well-known instinct in animals—has fascinated researchers for years. This study focused on the homing ability of the oriental butterflyfish Chaetodon auripes. We tagged 24 specimens ranging from 12.2 to 16.6 cm in total length. Of these, eight were recaptured near their origin after being displaced over distances of < 500 m, which was potentially outside their expected home range. Displacement distance or body size had no significant effect on their homing ratio. Butterflyfish could be new candidates as a model species for further investigation of homing behaviour.