Influence of temperature on hatching success of skipjack tuna (Katsuwonus pelamis): Implications for spawning availability of warm habitats.

Exploring the effects of water temperature on egg development in skipjack tuna (Katsuwonus pelamis) has substantial implications for evaluations of wild spawning habitats. In the present study, we examined the hatching success and duration as a function of temperature from 21 to 33°C under captive environments. A high hatching rate of over 50% between 23 and 31°C was observed, with the shortest hatching duration at 31°C. Because the egg period is vulnerable to predators, a shortened hatching duration with warming water would be ecologically advantageous for K. pelamis, as its main spawning grounds are located in tropical areas.

Rapid endothermal development of juvenile pacific bluefin tuna.

An important trait of Pacific bluefin tuna (PBT) is their ability to maintain their body temperature above the ambient temperature, which allows them to occupy a wider ecological niche. However, the size at which this ability in nature develops is unclear. Therefore, this study aimed to clarify this point by monitoring the body temperature and the surrounding ambient temperature as the fish grew. PBT with fork lengths (FLs) ranging from 19.5 to 28.0 cm were implanted with archival electronic tags and released into the ocean. Data from 41 fish were obtained (recorded body and water temperatures, light level, and swimming depth (pressure) at 30-s intervals) and analyzed to elucidate the development of the ability of PBT to maintain a high body temperature. Body temperature of a PBT (< FL of ca. 40 cm) decreased in response to a vertical movement down to cooler depths, but higher body temperatures were maintained as the fish grew. The body temperature was then continuously maintained above ambient temperatures and fluctuated independently when fish attained more than 40 cm FL. Estimation of the whole-body heat-transfer coefficient and heat-production rate indicated that the latter decreased slowly with growth, while the former decreased by one order of magnitude when tuna reached 52 cm FL. Additionally, in the daytime, the whole-body heat-transfer coefficient was significantly higher than that at nighttime. Unlike other fishes including other Thunnus species, inhabiting tropical/subtropical waters, PBT rapidly acquire higher thermo-conservation ability when young, allowing capture of high-quality prey abundant in temperate waters to support high growth rates during early life.

Wheat Germ Agglutinin (WGA)-SDS-PAGE: A Novel Method for the Detection of O-GlcNAc-modified Proteins by Lectin Affinity Gel Electrophoresis.

Diverse cytoplasmic and nuclear proteins dynamically change their molecular functions by O-linked ß-N-acetylglucosamine (O-GlcNAc) modification on serine and/or threonine residues. Evaluation of the O-GlcNAcylation level of a specific protein, however, needs multiple and time-consuming steps if using conventional methods (e.g., immune-purification, mass spectrometric analysis). To overcome this drawback, we developed the following easy and rapid method for detection of O-GlcNAcylated proteins of interest. An O-GlcNAc affinity gel layer containing wheat germ agglutinin (WGA), a GlcNAc-specific lectin, selectively induces retardation of the mobility of O-GlcNAcylated proteins during electrophoresis. This WGA-layer thereby separates O-GlcNAcylated and non-modified forms of proteins, allowing the detection and quantification of the O-GlcNAcylation level of these proteins. This new method therefore provides qualitative and quantitative analysis of O-GlcNAcylated proteins in a relatively shorter time compared to conventional methods.

WGA-based lectin affinity gel electrophoresis: A novel method for the detection of O-GlcNAc-modified proteins.

Post-translational modification with O-linked ß-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.

The influence of body size on the intermittent locomotion of a pelagic schooling fish.

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.