Audrey Daning Tuzan

Feeding behavior under dark conditions in larvae of sutchi catfish Pangasianodon hypophthalmus

Sutchi catfish Pangasianodon hypophthalmus hatch with morphologically immature sensory organs; however, sensory organs develop rapidly with larval growth. Two-day-old larvae commenced ingesting Artemia nauplii. The larvae displayed many taste buds on the barbels, the head surface, and in the buccal cavity. Other sense organs were also well developed at this stage. Feeding experiments revealed that 2-day-old larvae ingested Artemia under both light and dark conditions, moreover, the larvae could ingest frozen dead Artemia. The ingestion rates for 4- and 7-day-old larvae were significantly higher under dark conditions than under light conditions. The rates using frozen dead Artemia were mostly higher than the rates using live Artemia. Therefore, feeding behavior under dark conditions is most likely not mediated by visual or mechanical senses, but rather by chemosensory senses, such as taste buds. Larval fish are vulnerable to predators; thus, if they can search for and eat food at night, they can avoid diurnal predators. The behavior observed here appears to represent their survival strategy. Moreover, these results suggest a new possibility that sutchi catfish larvae can be reared under dark or dim light conditions in order to improve survival and growth rates as in the case of African catfish Clarias gariepinus.

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.