Morphogenesis of free neuromasts in the larvae of brown-marbled grouper epinephelus fuscoguttatus

Newly hatched larvae had one pair of free neuromasts behind the eyes. As the larvae grew, free neuromasts increased in number. Theapical surface of sensory epithelium widened and subsequentlyelongated. The number of sensory hair cells increased and thedirections of maximum sensitivity became both anteroposteriorand dorsoventral on the trunk. Before notochord flexion, only the anteroposterior type was observed. After notochord flexion, two types of neuromasts were observed on the trunk. On the head, the orientation of free neuromasts formed a tangential line to concentric circles around the eyes and nostrils. Free neuromasts on the head could therefore receive stimuli from various angles from predators or zooplanktons. This suggests that these free neuromasts play a role in compensating for a dead angle of vision, and an important role in detecting zooplankton under scotopic vision. Canal organs were observed on the head and operculum in 40-d-old animals

Optimum light intensity for larval rearing of brown marbled grouper Epinephelus fuscogttatus

Brown-marbled grouper Epinephelus fuscogttatus hachted with immature sensory organs, however their sensory organs developed rapidly after hatching. Their eyes had only cone cells in their retinae until commencement of the methamorphosis. The brown-marbled grouper larvae got rod cells at 25-day-old, then, retinomotor responses occured in their retinae. The retinomotor responses occured between 0.1 lx and 1 lx. Feeding experiments showed that the larvae ingested Artemia with high ingestion rates in 10 lx and above. This study recommends the light intensities of 100 lx to 1000 lx for larval rearing of brown marbled grouper

Visual thresholds for feeding and optimum light intensity for larval rearing of Asian seabass, Lates calcarifer (Bloch)

This study examined the retinomotor responses and prey ingestion rates of 10-, 15-, 20- and 30-day-old Asian seabass Lates calcarifer under different light intensities from 0 to 1000 lx to determine the visual thresholds. Subsequently, two age groups of seabass larvae were reared under light intensities of 10, 100 and 1000 lx to determine the optimum illumination in hatchery tanks. Retinomotor response was absent in 10-day-old larvae, but quite marked in 15- and 20-day-old seabass at 1 lx and higher. Ingestion of Artemia nauplii by 10-day-old larvae was almost zero at <1 lx, increased significantly at 1 lx, and was maximal at 10–100 lx. Artemia ingestion under dim light <1 lx improved with age, and older larvae took more prey in complete darkness due to the presence of rod cells (and also free neuromasts). Larvae from 13 to 26 days group had similar survival and growth at 10–1000 lx, however, from 5 to 10 days group showed similar survival rate with highest weight gain at 100 lx. Therefore, we recommend that hatchery rearing tanks be illuminated such that the larvae in the water are exposed to approximately100 lx

A study of protozoa distribution in Kuantan coastal areas

Seed production of marine finfish in Malaysia is still facing problems about the live feed of starter diets. Currently, we use S or SS-type rotifers, which have sizes from 100 to 200μm. Early-stage larvae of some marine finfish species select feed less than 100 μm. Protozoa is a collective term of aquatic microorganism that has been identified to be suitable live feed, as their body sizes are less than 100μm. Protozoa is considered to play an important role in microbial food chains. The objective of this study was to detect the suitable protozoa as the live feed from Kuantan coastal areas. Water samples were collected from three places in Kuantan coastal area, which were Pantai Teluk Cempedak, Pantai Sepat, and Pantai Cherok Paloh. The sample water was cultured in the beakers with nutrients for ten days. Various species protozoa were identified, e.g. Euplotes sp. Oxytricha fallax and Nassula microstoma. The sizes of the cultured protozoa range from 40 to 200µm. Protozoa with size less than 100µm were Euplotes sp., Nassula microstoma, and Colpidium colpoda. These protozoa species will be good candidates for live feeds for the larval rearing of marine finfis

Demand feeding system using an infrared light sensor for brown-marbled grouper juveniles, Epinephelus fuscoguttatus

In general, demand feeding devices are equipped with a mechanical trigger switch. Such a switch is not suitable for juvenile fish with a small body size, because the body weight is insufficient to trigger the feeder. An infrared light sensor that does not require the fish to push a feeder switch is more suitable for small fish. The brown-marbled grouper Epinephelus fuscoguttatus is an important fish species in Southeast Asia. The purpose of this study was to compare the growth rates (GRs) of brown-marbled grouper juveniles reared using customised demand feeding devices with an infrared light sensor (the infrared light demand feeder (IRDF) group) and automatic feeding devices (the automatic feeder (AF) group). The results indicated that GRs of standard lengths and body weights showed no significant differences using one-way analysis of variance; however, the standard length of the IRDF group showed a tendency of a higher GR than the AF group. Although the feed conversion ratio (FCR) also showed no significant difference, the FCR of the IRDF group was more efficient, indicating that the IRDF group yielded a more desirable FCR. These results indicate that IRDF can be used in the culture of brown-marbled grouper juveniles. In view of the working schedule of the fish farm staff, IRDF are superior to other feeding devices, because they are less labour-intensive than usual tasks. We conclude that IRDF is a useful feeding system for aquaculture

Aggressive behaviour of African catfish clarias gariepinus juveniles under different light intensities and light wavelengths

The survival and growth rates of African catfish (Clarias gariepinus) were reported to be affected by light conditions. One of the methods to understand the effects of light conditions on fish survival and growth rates is through analysing the aggressive behaviour of the fish. The objective of the present study was to analyse the aggressive behaviours of African catfish juveniles under different light intensities and light wavelengths. For this purpose, the behaviour of African catfish juveniles (average body weight = 0.45 ± 0.19; average total length = 35.2 ± 5.0) was observed under three light intensities (0.0014, 0.014, and 1.40 μmoles/m²/s) and five light wavelengths (white, blue, green, yellow, and red). The results showed that the aggressive behaviour of the fish was significantly affected by light intensities and light wavelengths. Among the three light intensities, the juveniles showed less aggressive behaviour under 0.0014 μmoles/m²/s. Furthermore, the juveniles also showed less aggressive behaviour under the yellow light. Therefore, the rearing of African catfish juveniles under of 0.0014 μmoles/m²/s and yellow light wavelength is recommended