Now showing items 1-3 of 3

    • Article

      Behavioural evidence for colour vision determined by conditioning in the purple mud crab Scylla tranquebarica 

      G Kawamura, TU Bagarinao, HS Cheah, H Saito, ASK Yong & LS Lim - Fisheries Science, 2020 - Springer Verlag
      Crabs and shrimps (order Decapoda) use colours in various tasks such as foraging and mate choice. Colour vision requires at least two types of photoreceptors with different spectral sensitivities. Previous physiological studies revealed that most crabs including Scylla mud crabs have a single visual receptor system, i.e. they are colour blind. We determined colour vision by means of a behavioural experiment on hatchery-produced and wild-captured purple mud crab Scylla tranquebarica in a roofed hatchery. Adult crabs (8-10 cm carapace width) were subjected to classical conditioning to associate a food reward with a blue or a green stimulus placed among seven shades of grey. The hatchery-produced crabs learnt this task after 14 days of reward training, and thereafter distinguished blue in 27 non-reward trials, and green in 39 non-reward trials. The wild-captured crabs did so after 25 days of reward training, and distinguished green in 49 non-reward trials. These results indicated colour vision in S. tranquebarica. However, the crabs were unable to distinguish blue or green in dim light of 4.4 cd/m2 (which is slightly brighter than full moon light). The high colour vision threshold was attributed to the small optic parameters of the apposition compound eyes of S. tranquebarica.
    • Article

      Fishing methods and gears in Panay Island, Philippines 

      G Kawamura & TU Bagarinao - Memoirs of Faculty of Fisheries Kagoshima University, 1980 - Faculty of Fisheries, Kagoshima University
      The authors surveyed the fishing methods and gears in Panay and smaller neighboring islands in the Philippines in September-December 1979 and in March-May 1980. This paper is a report on the fishing methods and gears used in these islands, with special focus on the traditional and primitive ones.
    • Article

      A fundamental study on the behavior of milkfish fry for improving the efficiency of traditional fry collecting gear in the Philippines 

      G Kawamura, S Hara & TU Bagarinao - Memoirs of the Kagoshima University Research Center for the South Pacific, 1980 - Kagoshima University Research Center for the South Pacific
      The reaction of milkfish fry to miving and stationary nets of different meshes and colors in an experimental tank was determined. The underwater visibility of the nets saw measured and the water filtration in a fry-sweeper was observed.

      Milkfish fry were both driven well by the moving nets and retained well by the stationary nets, with the fine-meshed black net most effective in both cases. The white and blue nets were found to be quite invisible to the fry in the blue-painted tank, particularly under contour lighting conditions; the black net was found to be very visible to the fry under both surface and contour light. The underwater visibility of the nets was found to vary with the sea conditions and the light direction. Water filteration in the fry-sweeper was found to be almost perfect.

      From the results, it was concluded that milkfish fry are caught by the moving fry collecting gear through driving and not by filtering. Since fry collection grounds are usually turbid, it was recommended that dark-colored materials be used for effective driving. It is also deemed much better to use larger mesh nets in the wings of the fry gear to minimize net resistance in the water and facilitate operation.