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To evade predators, many prey perform rapid escape movements. The resulting escape trajectory (ET) – measured as the angle of escape direction relative to the predator’s approach path – plays a major role in avoiding predation. Previous geometrical models predict a single ET; however, many animals (fish and other animal taxa) show highly variable ETs with multiple preferred directions. Although such a high ET variability may confer unpredictability, preventing predators from adopting counter-strategies, the reasons why animals prefer specific multiple ETs remain unclear. Here, we constructed a novel geometrical model in which T diff (the time difference between the prey entering the safety zone and the predator reaching that entry point) is expected to be maximized. We tested this prediction by analyzing the escape responses of Pagrus major attacked by a dummy predator. At each initial body orientation of the prey relative to the predator, our model predicts a multimodal ET with an optimal ET at the maximum T diff ( T diff,1 ) and a suboptimal ET at a second local maximum of T diff ( T diff,2 ). Our experiments show that when T diff, 1 – T diff, 2 is negligible, the prey uses optimal or suboptimal ETs to a similar extent, in line with the idea of unpredictability. The experimentally observed ET distribution is consistent with the model, showing two large peaks at 110–130° and 170–180° away from the predator. Because various animal taxa show multiple preferred ETs similar to those observed here, this behavioral phenotype may result from convergent evolution that combines maximal T diff with a high level of unpredictability. Significance Statement Animals from many taxa escape from suddenly approaching threats, such as ambush predators, by using multiple preferred escape trajectories. However, the reason why these multiple preferred escape trajectories are used is still unknown. By fitting a newly constructed model to the empirical escape response data, we show that the seemingly complex multiple preferred escape trajectories can arise from a simple geometrical rule which maximizes the time difference between when the prey enters the safety zone and when the predator reaches that entry point. Our results open new avenues of investigation for understanding how animals choose their escape trajectories from behavioral and neurosensory perspectives.

Laboratory behavioural observation and computational fluid dynamics (CFD) analysis were conducted to examine whether the movement of the elongated dorsal and pelvic spines changed the hydrodynamic drag in white-streaked grouper Epinephelus ongus larvae. The behavioural observation in the tank revealed that the larvae extended the dorsal and pelvic spines during passive transport and retracted during swimming; the angles of the dorsal and pelvic spines in relation to the anteroposterior axis were larger during the passive transport (mean±s.d. = 28・84±14・27 and 20・35±15・05°) than those during the swimming (mean±s.d. = 2・59±5・55 and 0・32±6・49°). The CFD analysis indicated that the relative hydrodynamic drag acting on the larvae was approximately 1・25 times higher when the spines were extended (passive transport) than when the spines were retracted (swimming), suggesting that the E. ongus larvae have an ability to adjust their hydrodynamic drag depending on the behavioural context. Journal of Fish Biology, Journal of Fish Biology, 85(5), pp.1575-1765; 2014

We examined whether we could identify the feeding behaviours of the trophic generalist fish Epinephelus ongus on different prey types (crabs and fish) using a data logger that incorporated a three-axis gyroscope and a three-axis accelerometer. Feeding behaviours and other burst behaviours, including escape responses, intraspecific interactions and routine movements, were recorded from six E. ongus individuals using data loggers sampling at 200 Hz, and were validated by simultaneously recorded video images. For each data-logger record, we extracted 5 s of data when any of the three-axis accelerations exceeded absolute 2.0 g, to capture all feeding behaviours and other burst behaviours. Each feeding behaviour was then identified using a combination of parameters that were derived from the extracted data. Using decision trees with the parameters, high true identification rates (87.5% for both feeding behaviours) with low false identification rates (5% for crab-eating and 6.3% for fisheating) were achieved for both feeding behaviours., The Journal of Experimental Biology, 217(18), pp.3204-3208; 2014

Supporting information SI Materials and MethodsNumber of eggs and the size of femaleTo examine the relationship between the female size and number of egg, 154 fully matured female chum salmon (611 ± 35 mm fork length (LF)) collected in the Shibetsu River, Japan was used during 2009-2011. Fork length, body mass, number of eggs, and egg diameter and weight (n = 10 eggs per females) were recorded for each female. Counting number of eggs releasedTo counting the number of eggs released each spawning, twenty six fully matured female chum salmon (649 ± 47 mm fork length (LF)) collected in the Shibetsu River, Japan was used during 2003-2009. The spawning behavior of one female and one male was monitored in the spawning channel, and the positions of the nests were recorded. After the spawning behavior was completed, we dug up the nest and counted the number of eggs each nest.Fig S1. An example of a relationship between absorbance values and sperm concentrations diluted at 0.5, 1.0, 2.0 4.0, 8.0, 16.0, and 32.0 μl /ml with river water for fish c_48 (r 2= 0.97, p < 0.05). Fig S2. Relationship between vibration duration at sperm release and amount of sperm released collected by the condoms (16 ovipositions for 8 males and 9 females). The curve was fitted by: amount of sperm release = e(0.21×vibration duration at sperm release (sec)+ 2.59) using linear mixed models and p < 0.001 was estimated by using a likelihood ratio test compared with null model.Fig S3. Relationship between the amount of sperm released and male fork length. Data was obtained from 90 ovipositions for 39 males and 39 females.Fig S4. Relationship between the amount of sperm released and the log transformed duration between matings. The curve was fitted by: amount of sperm released = 14.57 × female fork length – 4.28 and p < 0.001 was estimated by using a likelihood ratio test compared with the null model. Data was obtained from 51 ovipositions for 31 males and 31 females.Fig S5. Relationship between the log transformed number of eggs released and the number of matings in females for first mating (a), second mating (b) and third mating (c). The curve was fitted by: log transformed number of eggs = 0.0039×female fork length +4.22 for first mating (95 % confidence interval (CI) for a coefficient ranging from 0.0035 to 0.0043 , p < 0.01: a), log transformed number of eggs = 0.0044×female fork length +3.82 for second mating (95 % CI for a coefficient ranging from 0.0040 to 0.0048 , p < 0.001: b), log transformed number of eggs = 0.0037×female fork length +3.93 for third mating (95 % CI for a coefficient ranging from 0.0032 to 0.0042, p < 0.001: c), respectively.

Several fish species show a strong homing ability and distinct site fidelity to their original habitats and spawning sites. While some pelagic fishes exhibit long-distance migration in an ocean, some site-specific fishes show homing and site fidelity behaviors within a small home range (e.g. < 1 km2). Fine-scale monitoring (accuracy: meters) of movements contributes to the understanding of homing and site fidelity behaviors particularly for the site-specific fishes. We have studied the homing and site fidelity behaviors of the black rockfish which is a typical site-specific fish. In 2004, we tried to monitor fine-scale movements of the rockfish using a positioning telemetry system and introduce the results in this paper., February 23-25, 2010, Phuket, Thailand

Juvenile and young hatchery-reared Mekong giant catfish Pangasianodon gigas have been released into reservoirs throughout Thailand. For the sustainable reservoir fishery of the giant catfish, new science-based fishery management measures are expected in Thailand, such as the establishment of protected areas. Therefore, the habitat use and movement patterns of the hatchery-reared giant catfish have been investigated in the Mae Peum reservoir from 2003 to 2005. Our results suggest that the hatchery-reared fish spent their time in shallow depths above hypoxic water in the reservoir. The fish which have been reared in a fish pond may recognize and avoid hypoxic conditions., March 5-6, 2009, Bangkok, Thailand

In this study, the relationship between the breathing frequency and the dynamic body acceleration (DBA) of one hatchery-reared loggerhead turtle Carretta carretta was examined using acceleration data loggers. Two acceleration data loggers (M190L-D2GT, W1000-3MPD3GT, Little Leonard, Japan) were attached on the lower-beak and carapace of a hatchery-reared loggerhead turtle, respectively. Breathing was successfully detected from the angle and depth of the beak-attached data logger and DBA, which has been used as an index of activity levels (Wilson et al., 2006), was calculated from the forward acceleration of the carapace-attached logger. There was a positive correlation between the DBA in the previous dive and the breathing frequency; the relationship was exponential. The result suggests that the number of breaths increased exponentially after a more active dive., March 5-6, 2009, Bangkok, Thailand