Determination of visual axis of tiger grouper juveniles Epinephelus fuscoguttatus, to develop a demand feeding system

In a demand feeding system, the fish turn on the switch of the feeder to get feed. In order to develop a demand feeding system with an infrared light sensor to which juvenile tiger grouper, Epinephelus fuscoguttatus visually respond, the visual acuity and visual axis of the juveniles were determined to obtain fundamental understanding of their vision. Three farmed juveniles were anaesthetized with MS222 and fixed in Bouin’s solution. The left retinae of each juvenile were cut into nine regions (Figure 1). The specimens were embedded in paraffin, cut into 6 μm thick tangential sections, and stained with haematoxylin-eosin. The density of cone cells (0.01mm2) in each region was counted in the stained sections. Visual acuity was calculated using cone cell densities and lens diameter. The highest cone density of each juvenile was 359 (bottom, B), 394 (temporal, T) and 380 cells/0.01mm2 (temporal, T) respectively. The estimated minimum separable angles of the highest density regions were 4.312×10-3, 3.661×10-3, 3.592×10-3 radian in each juvenile respectively. The estimated visual acuities were 0.068, 0.080 and 0.081 in those regions. These results showed that the visual axis of tiger grouper juveniles was in forward

Determination of visual acuity and visual axis of brown-marbled grouper, epinephelus fuscoguttatus to develop a demand feeding system

The visual acuity and visual axis of juvenile brown-marbled grouper, Epinephelus fuscoguttatus were determined to get the understanding of their vision in order to develop a demand feeding system. Three juveniles were anaesthetised with MS222 and fixed in Bouin’s solution. The left retina of each juvenile was cut into nine regions – the dorso-nasal (DN), dorsal (D), dorso-temporal (DT), nasal (N), bottom (B), temporal (T), ventro-nasal (VN), ventral (V), and ventro-temporal (VT). The specimens were embedded in paraffin, cut into 6 μm thick tangential sections, and stained with haematoxylin-eosin. The density of cone cells (0.01 mm2) in each region was counted in the stained sections. Visual acuity was calculated using cone cell densities and lens diameter. The highest cone cell densities of each of the juveniles were 359 (bottom, B), 394 (temporal, T), and 380 cells/0.01 mm2 (temporal, T), respectively. The estimated visual acuities were 0.068-0.081 in those regions, respectively. These results showed that the visual axis of brown-marbled grouper juveniles was forward. Therefore, the position of the target switch of demand feeding system was set at 2 cm below the water surface

Reduced cannibalistic behavior of African catfish, clarias gariepinus, larvae under dark and dim conditions

In general, African catfish shows higher survival rates in the dark conditions than in the light conditions. In this study, larval behavior of African catfish was observed under 0, 0.01, 0.1, 1, 10, and 100 lx using a CCD camera to investigate the reason why African catfish larvae show higher survival rates in dark conditions. The larvae showed significantly higher swimming activity under 0, 0.01, and 0.1 lx than that under 10 and 100 lx. The larvae also showed significantly increased aggressive behavior under 10 and 100 lx; the swimming larvae attacked resting individuals more frequently under 10 and 100 lx than under 0, 0.01, and 0.1 lx. The aggressive behavior and sharp teeth of the attacking larvae appeared to induce skin surface lesions on injured larvae. Chemical substances were then generated from the injured skin surface, and these chemical stimuli triggered cannibalistic behavior in other fish near the injured fish. The results of this study demonstrate that the higher survival rates of African catfish larvae under dark conditions are a result of inactivity and subsequent increase in chemical releasing stimuli concentrations around inactive individuals that triggers feeding behavior in nearby active catfish. Therefore, we recommend larval rearing of African catfish in dark or dim conditions, as it improves catfish survival rates

Taste preference of hybrid grouper (Epinephelus fuscoguttatus♀×Epinephelus lanceolatus♂) for nucleoside and nucleotides

This study was conducted to determine the taste preference of hybrid grouper (Epinephelus fuscoguttatus ×Epinepheluslanceolatus) for nucleoside (inosine -INO) and nucleotides (inosine-5’-monophosphate –IMP and guanosine-5’-monophosphate -GMP), which are commonly used as feeding stimulants in fish diets. Behavioural assay was conducted by feeding the fish with the agar gel pellets that contained the taste substances and observing their feeding response through video recording. Preference Index (PrfInd; minimum = 0, maximum = 1) was calculated to evaluate the fish preference for the taste substances tested. Data so collected suggested that INO, IMP, and GMP were generally preferable by the hybrid grouper. However, INO was the most potential FS for both S and L sizes (19.7 ± 1.4 g and 162.3 ± 50.5 g in BW, mean ± S.D.) hybrid grouper based on its functional dosage. In the S size fish, INO attained high PrfInd at both 0.1% and 1% (0.84 and 1) concentration levels, while IMP and GMP attained high PrfInd at 1% (both 1) but low PrfInd (0.6 and 0.13, respectively) at 0.1%. In the L size fish, INO also attained very high PrfInd at 0.01% (0.87) but IMP and GMP were not (0.13 and 0). In addition, improvement in the taste acceptance to INO of the hybrid grouper was evident in this study. The S size fish rejected INO at 0.01% (PrfInd= 0) but the L size fish accept edit very well (0.87). These results suggested that the supplementation level of INO in the practical diets for the hybrid grouper can be decreased with the fish growth during the grow-out period

Demand feeding system for juveniles of groupers, brown-marbled grouper and orange-spotted grouper

Demand feeding is a new feeding method by which fish can feed themselves. Fish switch on the feeding device when they require food. This method has several advantages because the fish can eat when they are most motivated to feed. The system can thus minimize feed loss and reduce water pollution. The demand feeding system has been studied for ten years, but so far, there are only a few commercialized feeding devices. Currently, the most urgent issue facing the aquaculture industry in Malaysia is seed production, especially, groupers. This study was conducted to examine juvenile rearing by demand feeding system with brown-marbled grouper Epinephelus fuscoguttatus and orange-spotted grouper, Epinephelus coioides. 10 juveniles were kept in a 500 L round polyethylene tank (nine tanks, 90 fish). The tanks had water running system with water change (90%) every morning. Throughout the experiment, fish were exposed to natural photoperiod. Water temperature was 26.5 – 30.5 °C and salinity was 26-29 ppt. During rearing experiment, the fish were fed with pellets (Otohime EP3, Marubeni Nisshin Feed Co. Ltd.). Three experimental groups, pendulum demand feeder group (PDF, FH221, Aquatic Eco-Systems, Inc.), infrared sensor demand feeder group (IRDF) and automatic feeder group (AF) were set with three replicates. The IRDF consisted of an infrared sensor (infrared light 860 nm) ending in a red pellet-like knob with food container. Both demand feeders (PDF and IRDF) were set to dispense 10-15 pellets when fish activated the trigger (pendulum rod and infrared sensor respectively) located 2 cm below the water surface. The automatic feeder (AF) was set to dispense 130-150 pellets at 08:00 and 17:00 h. The experiment lasted for 20 days. Fish growth rates; total length (TL) and body weight (BW) were compared. Fish growth of three experimental groups of each grouper was obtained. In the experiment of brown marbled grouper, total length of IRDF group was higher than that of PDF group (P<0.05). BW growth rates of three groups were not significant different. In the experiment of orange-spotted, there are no significant differences, but TL and BW growth rates of IRDF group showed higher tendency than that of AF and PDF groups. Therefore, IRDF demand feeding devises are suitable for juvenile rearing of groupers