Limit of colour vision in dim light in larvae of the giant freshwater prawn <Emphasis Type="Italic">Macrobrachium rosenbergii</Emphasis>

Colour vision depends on sufficient ambient light and becomes ineffective at a particular low light intensity. It is not known how decapod crustaceans see colour in dim light. In the present study we investigated the colour vision threshold in larvae of the giant freshwater prawn Macrobrachium rosenbergii in a tank under natural illumination. Plastic beads of different colours (blue, red, yellow and white) in various combinations were suspended in the tank. The larvae swam straight toward the beads and gathered around them. The number of larvae was highest on the blue and white beads. The luminance in the tank was then gradually decreased by covering it with different numbers of layers of black cloth, and the response of the larvae to the beads was video-recorded under infrared illumination. The preference for blue and white beads remained manifest as the luminance was reduced from 418 to 0.07 cd/m², but not at 0.02 cd/m², indicating a colour vision threshold between 0.07 and 0.02 cd/m². The larvae have apposition compound eyes with large optical parameters, comparable to those of apposition eyes of nocturnal insects, which presumably capture more light and show enhanced sensitivity, enabling the larvae to see colour in dim light.     

Touch-sensitive bristles on the carapace of the mud crab Scylla paramamosain may be receptors for courtship signals

Fisheries Science - Bristle patches on the carapace behind the eyes were found for the first time in both males and females of the four species of mud crab Scylla spp. Electrocardiography revealed...     

Evaluation on the potential of betaine,taurine, nucleotide and nucleoside as feeding stimulant for juvenile marble goby <Emphasis Type="Italic">Oxyeleotris marmoratus</Emphasis> through behavioural assays

This study was conducted to evaluate the potential of betaine, taurine, inosine (INO), inosine 5′-monophosphate disodium (IMP·Na₂), and guanosine 5′-monophosphate disodium (GMP·Na₂) as a feeding stimulant for juvenile marble goby (Oxyeleotris marmoratus) (total length 6.6–8.5 cm) through behavioural assays using agar gel pellets. All fish were conditioned to accept agar gel pellet before the behavioural assays started. Each chemical substance was tested on 50 replicates of individual fish once, and the overall ingestion rate was calculated as the representative data. The pure agar gel pellet was totally rejected by the fish (0 % ingestion rate). Therefore, any added test substance which can significantly improve the fish ingestion of the agar gel pellet can be the potential feeding stimulant. Of all the chemical substances tested at 0.1 M concentration, the ingestion rates of both INO and IMP·Na₂ were the highest (both 100 %) and were significantly higher (P < 0.05) than those of the other chemical substances tested. However, INO was identified as the most potent feeding stimulant as it could function perfectly (100 %) even at the lower concentrations tested (0.01 and 0.001 M). The ingestion rates of IMP·Na₂ were found significantly decreased (P < 0.05) at the concentrations of 0.01 and 0.001 M (78 and 2 %, respectively). The ingestion rate of GMP·Na₂ at 0.1 M was 60 %, hence higher concentration (>0.1 M) may be required to improve its efficiency as the feeding stimulant. Taurine was not a feeding stimulant, and betaine was neither a feeding stimulant nor feed enhancer for the juvenile O. marmoratus.     

Remarkably high ingestion ratio of acidic food in juvenile marble goby,Oxyeleotris marmorata

International Aquatic Research - Behavioral test was conducted to determine the level of food pH which was preferable by the juvenile marble goby, Oxyeleotris marmorata (50 individuals or...