Leong-Seng Lim

Betaine is a feed enhancer for juvenile grouper (Epinephelus fuscoguttatus) as determined behaviourally

ABSTRACT The present study aimed to determine if betaine can function as a feeding stimulant or feed enhancer for the juvenile grouper, Epinephelus fuscoguttatus through a behavioural experiment with video recording. Agar gel pellet was used as the medium to deliver the chemical test substances – betaine (BET), amino acids mixture (AAM) and mixtures of 1:1, 1:2, 1:3, 1:4, 1:5 BET + AAM to the fish. The pure agar gel (PAG) and feed extract pellets were used as the negative and positive control, respectively. From the recorded videos, two parameters were observed: (I) the pellet was consumed or rejected [A] – if consumed, recorded 1; if rejected, recorded 0, and (II) frequency of the pellet has been captured before it was consumed or rejected and ignored [B], and the preference index was calculated through [A]/[B]. The PAG pellet was totally rejected by the fish (indexs value = 0). The indexs values of BET and AAM were 0.17 ± 0.39 and 0.19 ± 0.31 (mean ± SD), respectively. No significant difference was found among the indexs values of PAG, BET and AAM pellets. However, the indexs values of all BET + AAM pellets (1:1–1:5) were very high (0.60–0.90), and were significantly higher than those of the PAG, BET and AAM pellets. No significant difference was found among the indexs value of 1:1, 1:2, 1:3 and 1:4 BET + AAM treatments. These results concluded that betaine is a feed enhancer for the E. fuscoguttatus and little amount of betaine supplementation is sufficient to enhance the flavour of amino acids mixture.

Morphogenesis of sense organs and behavioural changes in larvae of the brown-marbled grouper Epinephelus fuscoguttatus (Forsskål)

The morphogenesis of sense organs and related behavioural changes in the hatchery-reared brown-marbled grouper Epinephelus fuscoguttatus larvae were examined to gain better understanding of its early life history because ecological field observations for grouper species is difficult. The newly hatched larvae (2.1 mm total length) had developing eyes and otic vesicles, a pair of free neuromast on the head and ciliated olfactory epithelium. At 3 days post hatching (dph), the eyes became fully pigmented with pure-cone retinae, the semicircular canals formed in the inner ear, and the larvae (2.8 mm) were able to swim horizontally, preying on rotifers. Retinal rods and the intra-oral taste buds at pharyngeal appeared next. The olfactory lamellae and the head lateral line system then formed, and the inner ears developed completely in the larvae during the metamorphosis period (15–40 dph; 5.1–18.1 mm). At settlement (50 dph; 32.8 mm), the fish possessed taste buds in the mouth entrance region, and the lateral line system developed completely. The sensory development correlates well with the known aspects of its life history at sea whereby the larvae can feed early and avoid predators during the passive drift, are able to swim shoreward to search nursery ground along the metamorphosis stage and survive in seagrass beds at settlement.

Low ph water impairs the tactile sense of the postlarvae of the giant freshwater prawn Macrobrachium rosenbergii

The effect of low pH on the tactile sense of Macrobrachium rosenbergii postlarvae was determined in the laboratory by means of two behavioural assays: shelter (netting) occupancy and jumping response to touch stimuli (taps) by a glass micropipette. The postlarvae were acclimated to pH 4, pH 5, pH 6 and pH 7.5 (control) in 45 L aquaria 5–7 d before the experiments. Shelter occupancy decreased with pH and was significantly lower at pH 4 and pH 5 than at pH 6 and in the control. The jumping response instantly followed a tap 93–98% of the time in the control, pH 6 and pH 5 treatments. However, the postlarvae showed significantly lower jumping response (65%) at pH 4, indicating an impaired tactile sense. Low pH 4–5 probably degrades the chitin of the sensory setae and inhibits the surface mechanoreceptors of the prawn postlarvae.