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The present study aimed to evaluate the feeding performance of juvenile marble goby (Oxyeleotris marmorata) on acidified diets. Five fish meal-based diets at various pH levels (2.5, 3.2, 4.3, 5.3, and 6.0 (control)) were prepared, and each of them was fed to 10 wild-caught O. marmorata juveniles (body length 7.7-9.3 cm; each fish was placed in an aquarium, hence each dietary treatment was in 10 replicates) for 20 days. Throughout the feeding trial, O. marmorata juveniles showed clear increments in the daily ingestion ratio (IR) values of AD 2.5, AD 3.2, and AD 4.3. The control diet and AD 5.3 were almost totally rejected by the fish. On day 20, the IR of AD 2.5 (0.46) and AD 3.2 (0.36) were significantly higher (P < 0.05) than those of AD 5.3 (0.1) and the control diet (0.02). In addition, 70% of fish fed AD 2.5 achieved a high IR value (0.6-1.0), and this was the best result among all the treatments (AD 3.2, 60%; AD 4.3 50%; AD 5.3 and control, 10%). These results suggested that acidified diets can be used to wean O. marmorata juveniles, and the recommended pH level was 2.5.

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.

This paper reports on the innate colour preference and colour vision in the hatchery-reared larvae (10–16 days old, stages IV–VIII) of the giant freshwater prawn Macrobrachium rosenbergii (De Man) based on their response to coloured beads in a grey-walled tank under natural illumination. Plastic beads (4.1 mm in diameter) of different colours (dark blue, light blue, light green, yellow, red, white, black, and grey) in various combinations were suspended in the water 5 cm from the water surface and 12–20 cm from the tank walls where the larvae rested in the absence of aeration. The larvae swam head first straight toward the beads and gathered around them. The number of larvae was highest around the dark blue, light blue, and white beads; lowest around the black, red, and light green beads; and moderate around the yellow bead. Tests with different colours in combination with three shades of grey indicated that the larvae of M. rosenbergii discriminated colours by chromaticity. The preference for blue seemed to be an innate rather than a learned ability since the larvae did not prefer the yellow and red beads that were more similar to the colours of the egg custard and the Artemia nauplii on which they had been reared.

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 (index’s value = 0). The index’s 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 index’s values of PAG, BET and AAM pellets. However, the index’s 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 index’s 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.

This study was conducted to evaluate the acceptability of hybrid grouper, Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂ on diets with different inclusion levels of soybean meal. A total of five dietary treatments with 0, 30, 40, 60, and 80% of fish meal protein replaced by soybean meal (SBM) protein (namely SBM0, SBM30, SBM40, SBM60, and SBM80, respectively) were fed to triplicate groups of fish for 14 days, and the feed intake, weight gain, specific growth rate, and survival were evaluated. The overall feed intake (mean ± SD, n = 3) of fish fed all dietary treatments with SBM inclusion (SBM30, 13.6±0.9 g fish-1; SBM40, 14.3±1.6 g fish-1; SBM60, 13.9±1.6 g fish-1) were not significantly different (p > 0.05) with that of the SBM0 (15.4±1.2 g fish-1), except SBM80 (9.4±2.9 g fish-1). The fish acceptance to SBM30, SBM40, and SBM60 were also as good as the SBM0 diet in the feed intake calculated once every 2 days. The fish fully accepted SBM30, SBM40, and SBM60 diets after 2 weeks as the feed intake at 14-d were significantly higher (p < 0.05) than those at 2-d, similarly to the SBM0. In conclusion, the hybrid grouper can accept diets with maximum SBM inclusion level at 60% without any diets palatability problem. However, the fish fed SBM40 and SBM60 showed significantly lower (p < 0.05) weight gain and specific growth rate than the fish fed SBM0, respectively. These results confirmed the poor utilization of SBM40 and SBM60 by the fish. Therefore, the research focus in future to develop practical diets with high SBM inclusion level for this hybrid grouper should be emphasized to improve the feed utilization instead of the diets palatability. © 2016 BIOFLUX SRL. All Rights Reserved.

Many demersal fish species undergo vertical shifts in habitats during ontogeny especially after larval metamorphosis. The visual spectral sensitivity shifts with the habitat, indicating a change in colour vision. Colour vision depends on sufficient ambient light and becomes ineffective at a particular low light intensity. It is not known how fishes see colour in dim light. By means of a behavioural experiment on larval African catfish Clarias gariepinus in the laboratory, we determined colour vision and colour discrimination in dim light. Light-adapted larvae were subjected to classical conditioning to associate a reward feed with a green or a red stimulus placed among 7 shades of grey. The larvae learned this visual task after 70 and 90 trials. A different batch of larvae were trained to discriminate between green and red and then tested for the ability to discriminate between these colours, as the light intensity was reduced. The larvae learned this visual task after 110 trials in bright light and were able to discriminate colours, as light was dimmed until 0.01 lx, the minimal illuminance measurable in this study, and similar to starlight. The retinae of the larvae were found to be light adapted at 0.01 lx; thus indicating cone-based colour vision at this illuminance. For comparison, three human subjects were tested under similar conditions and showed a colour vision threshold at between 1.5 and 0.1 lx. For the larvae of C. gariepinus, the ability of colour discrimination in dim light is probably due to its retinal tapetum, which could increase the sensitivity of cones.

Newly hatched larvae had one pair of free neuromasts behind the eyes. As the larvae grew, free neuromasts increased in number. The apical surface of sensory epithelium widened and subsequently elongated. The number of sensory hair cells increased and the directions of maximum sensitivity became both anteroposterior and 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.

The potential of tempeh (TMP) with supplementation of methionine (Met) and lysine (Lys) as a substitute of fishmeal (FM) was evaluated based on the growth performance and feed utilization for tiger grouper (Epinephelus fuscoguttatus) juveniles. Three diets were formulated to replace FM with TMP at 0% (D1, control diet), 40% without essential amino acids (EAAs) supplementation (D2) and 40% with EAAs supplementation (D3, 0.5% of Met and 0.5% of Lys) and fed to triplicate groups of fish (22.90±0.48g) twice a day for 8 weeks. Weight gain (WG), specific growth rate (SGR) and feed intake (FI) of D1 group (114.31%, 1.59%, and 45.51 g fish-1 , respectively) were significantly higher than those fed with TMP-based diets (P<0.05). On the other hand, supplementation of EAAs in D3 was able to significantly improve the protein efficiency ratio (PER) and net protein utilization (NPU) (1.17% and 23.13%, respectively) compared to other diets (P<0.05). Supplementation of EAAs reduced whole-body lipid (P<0.05) but slightly increased whole body protein (P>0.05) of the fish. In the present study, results indicated that supplementation of EAAs was only able to improve feed utilization (PER and NPU) but not in growth performance (WG and SGR) of E. fuscoguttatus fed on TMP-based diets.

This paper reports on the innate colour preference and colour vision in the hatchery-reared larvae (10–16 days old, stages IV–VIII) of the giant freshwater prawn Macrobrachium rosenbergii (De Man) based on their response to coloured beads in a grey-walled tank under natural illumination. Plastic beads (4.1 mm in diameter) of different colours (dark blue, light blue, light green, yellow, red, white, black, and grey) in various combinations were suspended in the water 5 cm from the water surface and 12–20 cm from the tank walls where the larvae rested in the absence of aeration. The larvae swam head first straight toward the beads and gathered around them. The number of larvae was highest around the dark blue, light blue, and white beads; lowest around the black, red, and light green beads; and moderate around the yellow bead. Tests with different colours in combination with three shades of grey indicated that the larvae of M. rosenbergii discriminated colours by chromaticity. The preference for blue seemed to be an innate rather than a learned ability since the larvae did not prefer the yellow and red beads that were more similar to the colours of the egg custard and the Artemia nauplii on which they had been reared.

Research in the application of fundamental concepts of fish behaviour to aquaculture has intensified recently and this chapter further elucidates fish sensory systems and functions and their involvement in the success or failure of hatchery and farm operations. Most marine fishes hatch with rudimentary sense organs that are elaborated by the time of first feeding and further improved with growth; thus, hatcheries must have the appropriate food, light and water currents for proper larval development. In grow-out farms, the ambient conditions must be at optimum or tolerable levels for the fish stock and the diets must have the right sensory characteristics to stimulate efficient feeding. Stressors for fish sensory systems include crowding, turbidity, underwater noise, chemotherapeutants, extreme pH, gas supersaturation and infection. High-density farms are stressful because the fish can sense, but cannot escape from, unfavourable conditions. Monitoring fish behaviour provides early warning of stress and disease and helps avert mortality and financial losses in aquaculture.

Acidification of rain water caused by air pollutants is now recognized as a serious threat to aquatic ecosystems. We examined the effects of low pH (control pH 7.5, pH 6, pH 5, pH 4) on the survival, growth, and shell quality of Macrobrachium rosenbergii postlarvae and early juveniles in the laboratory. Hatcheryproduced postlarvae (PL 5) were stocked at 250 PL per aquarium, acclimated over 7 d to experimental pH adjusted with hydrochloric acid, and reared for 30 d. Dead specimens were removed and counted twice a day. After 27 d rearing, all specimens were measured for total length and body weight. Carapace quality was assessed by spectrophotometry. Survival of juveniles was highest at pH 6 (binomial 95% confidence interval 79 - 89%) followed by control pH 7.5 (56 - 68%) and pH 5 (50 - 60%) and was lowest for unmetamorphosed postlarvae and juveniles at pH 4 (43 - 49%). The final median total length and body weight of juveniles were similar at control pH 7.5 (18.2 TL, 50.2 mg BW) and pH 6 (17.7 mm TL, 45.0 mg BW) but significantly less at pH 5 (16.7 mm TL, 38.2 mg BW); at pH 4, the postlarvae did not metamorphose and measured only 9.8 mm TL, 29.3 mg BW. Length frequency distribution showed homogeneous growth at pH 6, positive skew at control pH 7.5 and pH 5, and extreme heterogeneity at pH 4. The carapace showed different transmittance spectra and lower total transmittance (i.e. thicker carapace) in juveniles at pH 7.5, pH 6, and pH 5 than in unmetamorphosed postlarvae and juveniles with thinner carapace at pH 4. Thus, survival, growth, size distribution, and carapace quality of M. rosenbergii postlarvae and early juveniles were negatively affected by pH 5 and especially pH 4. The thinner carapace of the survivors at pH 4 was mostly due to their small size and failure to metamorphose. Natural waters affected by acid rain could decimate M. rosenbergii populations in the wild.

The Epinephelinae groupers are strict carnivorous species. They are widely cultured in the Asia Pacific region as a result of high demand and market price especially in the live reed food fish trade. Groupers are commonly raised in net cages and fed with the unsustainable low value fish. Although this feeding practice has been gradually improved by using formulated diets, the production cost of these diets is high due to the increasing prices of fish meal and fish oil. In order to find sustainable replacements for these expensive commodities, research has been conducted to evaluate alternative ingredients effects on fish growth performances and immune function. This review covers different types of alternative ingredients tested on several species of juvenile grouper. In general, animal protein sources were able to replace fish meal at higher inclusion levels than plant protein sources. Lowered digestibility, deficiency in essential nutrients, and reduced palatability are major challenges in using alternative ingredients in grouper feeds.

Grouper aquaculture is expanding but most grouper farmers are challenged by high cost of feed input due to the dependency on the expensive fish meal. Soybean meal (SBM) has high potential to replace fish meal but at high inclusion levels, diets palatability is affected. The use of suitable feeding stimulant (via gustation) or attractant (via olfaction) in non-fish meal based diets might be able to Increase feed Intake. Amino adds and betaine are rommonly used as feeding stimulant and attractant in aquaculture feeds. Unfortunately, little Is known about the specific response of grouper to these substances. The present study aimed to investigate the chemical responses In the grouper (Epinephelus fuscoguttatus) to feeding stimulant and attractant and evaluate its potential to promote the intake on SBM-based diets through an electrophysiology (Experiment 1), two behavioural (Experiments 2 & 3) and a feeding experiments (Experiment 4). In experiment 1, cysteine was determined as the most sensitive amino add to the olfaction of grouper, followed by lysine and arginine at the concentration of 10·3 M through electro-olfactogram analysis. The threshold level of cysteine was also determined at 10·5 M. Experiment 2 was carried out to ronfirm the results of Experiment 1 through behavioural study. Cysteine yielded the highest frequency in both the swimming and food searching activities, indicating its suitability as food attractant. In this experiment, It was realized that olfaction may not play a very critical role In cultured grouper because they are visual feeder and food are always provided by the farmers. Besides, the decision In food ingestion is mediated by gustation. Consequently, identification of feeding stimulant Instead of attractant Is more appropriate for the cultured grouper. Therefore, Experiment 3 was ronducted to study the taste effect of betalne and the preference for amino adds In tiger grouper using video rerording and agar gel pellet as the delivery medium.

Length-weight relationship and relative condition factor of the pond-cultured spotted barb, Puntius binotatus were calculated to determine its growth and health conditions in order to evaluate the efficiency of present culture practice. The cultured fish were growing well in the ponds as they attained strong positive allometric growth as the b value was 3.356 (>3), and the linear relationship r2 value (0.96) was significant at level 0.01. Nevertheless, the relative condition value of the pond cultured fish (1.008) was lower than those of the wild fish caught from the Upper Kerian River and Serdang River. The fish from Upper Kerian River were in much better condition than the pond cultured fish. Such differences could be due to the gaps in the water quality between the ponds and the rivers. Further studies should be conducted to determine the optimum range of water parameters especially temperature, pH and total dissolved solution (TDS) level of the culture environment for this fish, in order to optimize its culture condition.

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.

Larvae and juveniles of barramundi Lates calcarifer (Bloch) were examined for the development of the retina, occurrence of the retinomotor response and retinal tapetum and change in eye size with age in days. The barramundi hatched with unpigmented non-functional eyes in which retinal cells had not yet differentiated into the various elements. Soon it was followed by rapid changes in the histology of the retina. Two-day-old larvae had a well-pigmented retina with area temporalis which would allow acute vision and prey attack in the nasal direction. At 10 days, rod cells and the retinal tapetum first appeared in the retina and the retinomotor response first occurred; these would allow feeding in dim light. The retinal tapetum moved in unison with the cones and the pigment epithelium during the retinomotor response. At 26 days, the horizontal cells were divided into two layers and the twin cones appeared. These changes in the eyes occurred concurrently or in anticipation of behavioural changes, such as the onset of the first feeding at 2 days, the shift of habitat from coastal waters to swamps at the notochord flexion stage at 7-15 days, the abrupt change in feeding behaviour from roving zooplanktivore to lurking predator at 25-30 days and a later shift of habitat from turbid swamps to open coastal or lake areas at the early juvenile stage.

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. © 2010 The Japanese Society of Fisheries Science.

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.

Development of sensory organs in tiger grouper, Epinephelus fuscogttatus was examined by means of light- and scanning electron- microscopy, to provide useful information on their ecology and larval rearing. In newly hatched larvae, the eyes were not pigmented. The inner ears were oval-shaped vesicles with two otoliths. The larvae floated motionless in the water column. However, a pair of well developed free neuromasts was found behind the eyes, and the larvae were capable to avoid an approaching transparent pipette. In three-day-old larvae, the eyes were morphologically completed without rod cells and they commenced feeding on rotifers. The three semicircular canals of the inner ears, which play a role in the balance regulation, were completed, and the larvae were capable to swim horizontally. In 2o-ctay-old larvae, taste buds appeared in the buccal cavity, and they commenced feeding on Artemia nauplii. In 4O-day-old larvae, rod cells appeared and the inner ears were morphologically completed. The larvae started to settle down to the bottom of the tank. In SO-day-old fish, canal neuromasts formed and taste buds were found on the lips and breathing valves. At this stage, the fish commenced feeding on minced fish and stay at the bottom of the tank. In 6O-dayold fish, anterior and posterior olfactory pits were formed. Apparently, sensory organs of tiger grouper were well-developed when they settled to the bottom of the tank