Miguel Vazquez Archdale

Comparative fishing trials for Charybdis japonica using collapsible box-shaped and dome-shaped pots

Comparative fishing trials were undertaken with two commercial collapsible pots for the crab Charybdis japonica. One pot was box-shaped with two slit entrances at the ends, while the other was dome-shaped with two open funnel entrances. Pots were placed at the bottom of a pond that is connected to Kagoshima Bay. Fishing trials were carried out using a 1-day soaking time; the bait used was mackerel. The box-shaped pot had higher catches of crabs and non-target organisms, ***DIRECT SUPPORT *** A02OT006 00004 but the number of large crabs (carapace width \s>8 cm) was almost half as many as that caught with the dome-shaped pot. The catch of non-target species was also greatly reduced in the dome-shaped pot, and fish caught were mostly enmeshed in the netting. The reduction in catches of small crabs and non-target organisms was due to the nature of the dome-shaped pot’s larger mesh size and open entrances, which allowed for escape. The dome-shaped pot seemed more efficient for harvesting commercial size crabs, while the box-shaped pot seemed better for removing all crab sizes.

Morphology of the sense organs of anchovy Engraulis japonicus

The morphology of the lateral line system, the inner ear, the olfactory epithelium and the taste bud of the wild adult anchovy Engraulis japonicus was examined by photo microscopy and scanning electron microscopy. Hematoxylin solution was injected into the lateral line canals to show the arrangement of the lateral line system. The lateral line system has well-developed supraorbital, infraorbital and preoperculomandibular canals on the head, dense canal branches on the operculum, lateral line canals on the trunk, and no free neuromasts. The inner ear comprises three semicircular canals and three otholithic end organs: the sacculus, the lagena and the utriculus. The olfactory organs and taste buds were examined by scanning electron microscopy. The paired olfactory organs on the snout have rosettes of lamellae, whose sensory epithelium consists of receptor cells of both the ciliated and microvillous type. The taste buds are distributed only inside the mouth, and mostly between the teeth of the upper and lower jaws, and between the gill teeth on the gill rakers. Well-developed lateral lines on the head are advantageous for schooling, and the taste buds in the mouth and on the gill rakers are advantageous for filter-feeding on plankton.

Microhabitat distribution and behaviour of Branchiobdellidan Holtodrilus truncatus found on the freshwater shrimp Neocaridina spp. from the Sugo River, Japan

A study was performed on the microhabitat distribution and some aspects of behaviour of the ectosymbiotic branchiobdellidan Holtodrilus truncatus (Annelida, Clitellata) found on the freshwater shrimp that inhabit the Sugo River, Hyogo Prefecture, western Japan. Observations on shrimp that were collected from the Sugo River (2003 to 2011) confirmed that the host shrimp is Neocaridina spp. (Atyidae). The attachment location on the host shrimp was predominately between the 1st pleopod and the 5th pereopod (55.3%). The reproductive method of H. truncatus is hemaphroditism. The cocoon was found only inside the carapace of the host shrimp. The cocoon was transparent and contained a maximum of 14 juvenile worms (developing embryos). When hatching approached, H. truncatus’s worms became elongated and slender, and only one worm hatched out at a time. When Holtodrilus truncatus was removed from its host and was maintained in river water without any food, it survived for a maximum of 46 days. In a host exchange experiment, where we provided several other freshwater shrimp species, Palaemonidae fed on H. truncatus. Moreover, Palaemon paucidens and Macrobrachium nipponense from Lake Biwa also preyed upon H. truncatus. The possible symbiotic relationship between H. truncatus and Neocaridina spp. (family Atyidae) is further discussed.

Setae for Gill-Cleaning of Six Species of Japanese Sentinel Crabs (Macrophthalmus)

Abstract The setae involved in the gill-cleaning mechanism of six species of Japanese sentinel crabs are described. The setae are classified as belonging to five types: anchor, serrate, simple, digitate-scale-setule, and normal setule setae. The anchor setae are further divided into ten sub types based on the combinations of digitate-scale setule, normal setule, anchor type, and the shape of their tip. Setae on out-growths and tips were compared with those identified in previous studies. As a result, the single row half anchor setae were found only in the subgenus Macrophthalmus and might be used as a special characteristic in the subgenus.

Behavioural evidence for the use of geomagnetic cue in Japanese glass eel Anguilla japonica orientation

Japanese eel is already magnetosensitive at the glass eel phase. However, currently, there is no evidence that they can use geomagnetic cues for orientation. We examined orientation behaviour in a radially symmetrical test arena in which the horizontal component of the geomagnetic field could be manipulated. Groups of glass eels released at the centre of the arena showed a mean orientation angle significantly biased to the south of 198° in the ambient geomagnetic field, but showed random orientation in the geomagnetic field when its horizontal component was cancelled in a solenoid. Results showed that they use geomagnetic cues for orientation.

Morphological and functional characteristics of setae involved in grooming, water uptake and water circulation of the soldier crab Mictyris guinotae (Decapoda, Brachyura, Mictyridae)

This study was focused on the relationship between behaviour and morphological characters of the soldier crab Mictyris guinotae, using a functional morphological approach. The behaviour patterns of M. guinotae involved in water uptake and water-circulation were recorded by video camera and the setae involved in those two activities were described in detail. Furthermore, the crab’s grooming behaviour engaged in the cleaning of the surface of the third maxilliped was determined. The setae were classified into six types: denticulate, pappose, plumose, normally setulate, serrate, and simple setae. Among these, the denticulate setae were found on the chelipeds and the simple setae on the posterior margin of the carapace and on the anterior border of the first abdominal somite. M. guinotae inserted the setae located on the posterior border of the carapace margin and the anterior border of the first abdominal somite into the sandy substratum, and expelled water from its exhalant apertures and mouthparts. The water then flowed along the surface of the third maxilliped onto the abdomen. The crab exhibited a grooming behaviour to clean the surface of the third maxilliped after expelling water, by using the carpus and propodus of the cheliped when the surface of the third maxilliped had become covered by mud. We conclude that simple setae may have the function of collecting water from the substratum by capillary action, and the denticulate setae apparently have a grooming function. Moreover, also (the flow of) water may increase grooming efficiency, when the flow continues as the crabs groom the surface of their third maxilliped.