The effect of light intensity on early life development of common dentex Dentex dentex (L. 1758) larvae

The effects of different levels of illumination on common dentex Dentex dentex (L.) larvae have been examined. Illumination affected the relationships between total length and digestive tube length, total length and oil globule volume, and total length and yolk sac. The relationship between total length development and yolk sac utilization in dark and light conditions was found to be significant (P<0.05). However, it was determined that the relationship between digestive tube development and oil globule absorption was not significant (P>0.05). Besides, there is no effect of different light intensities on absorption of yolk sac and oil globule and digestive tube development (P>0.05). In addition, total length development was not significant (P>0.05). Survival rate was found to be not significantly different in dark conditions (P>0.05).     

Effect of feeding scheme and prey density on survival and development of Chinese mitten crab Eriocheir sinensis zoea larvae

The effect of feeding scheme and prey density on survival and development of Eriocheir sinensis zoea larvae was studied in three experiments. Different combinations and densities of rotifers (Brachionus rotundiformis) and newly hatched Artemia nauplii were fed to zoea larvae. Average survival at each stage, larval development (larval stage index, LSI), duration of zoeal stage and individual megalopa dry weight were compared among treatments. This study revealed that, under the experimental conditions, rotifers should be replaced with Artemia between the zoea 3 (Z3) and the zoea 4 (Z4) stage. The optimal rotifer feeding densities for zoea 1 (Z1) and zoea 2 (Z2) were 15 and 20 mL^?1 respectively, while the optimal Artemia feeding density for Z3, Z4 and zoea 5 (Z5) was 3, 5 and 8 mL^?1 respectively. Further trials in production scale are recommended.     

The effect of light intensity on first feeding of the spotted sand bass Paralabrax maculatofasciatus (Steindachner) larvae

The effects of light intensity on feeding incidence and prey consumption at first feeding of spotted sand bass larvae (Paralabrax maculatofasciatus Steindachner), using four light intensity treatments (0, 100, 400, and 700 lx) were evaluated. Specimens were fed the rotifer Brachionus plicatilis at a density of 3 rotifers mL^?1. One hour after the addition of prey, 30±3 (mean±SEM) larvae were sampled from each treatment aquarium. Feeding incidence was evaluated as the percentage of larvae with prey in the digestive tract. Feeding intensity was measured as the number of prey in the digestive tract of the larvae. Histological analysis was carried out to describe the eye structure at the time of first feeding. Larvae fed in darkness (0 lx) had a significantly lower (P<0.05) feeding incidence (1.2±2.2%) and intensity (0.4±0.7 rotifers larvae^?1) than those larvae fed at 100 (28±11%, 1.8±0.2 rotifers larvae^?1), 400 (48±10%, 2.4±0.3 rotifers larvae^?1), and 700 lx (52±4%, 2.4±0.1 rotifers larvae^?1). Feeding incidence of the spotted sand bass larvae increased with light intensity while the feeding intensity showed no significant difference (P>0.05) between light treatments. Histological analysis of the eye structure showed that first feeding larvae had well‐formed lens along with a retina composed of pure single cones as photoreceptors.     

Factors affecting the feeding response of larval southern bluefin tuna,Thunnus maccoyii (Castelnau, 1872)

Southern bluefin tuna, Thunnus maccoyii, are cultured in Australia following collection of wild juveniles. Hatchery culture from egg is in the experimental stage. High early mortality has hindered the production of quality juveniles in the hatchery. This study investigated the visual capacity of T. maccoyii during early larval ontogeny in order to describe the best larval rearing conditions to produce high‐quality seed stock. Functional visual ability, determined through behavioural experimentation, identified the effect of light intensity, prey density, turbidity, tank colour and turbulence on the feeding response. Larvae were visually challenged to feed under a range of conditions in short‐duration (4 h) feeding experiments. Feeding performance was measured as the proportion of larvae feeding and the intensity of feeding. First‐feeding performance was positively affected by increasing prey density and lower turbidities and unaffected by light intensity, tank colour, turbulence, prey size and larval density. The key findings from feeding experiments on 6 and 9 dph larvae was that as T. maccoyii aged, lower light intensities and higher prey densities significantly increased feeding performance. In addition, the study has identified that high light intensity and high air‐driven turbulence induced significant mortality. The proficient first‐feeding response indicated that early mortality common in culture is unlikely to be associated with a failure to initiate feeding. Our findings show the use of low light intensity has the potential to significantly improve survival and feeding response during the first two critical weeks of culture, when the major bottleneck in hatchery production is currently experienced.     

Effects of photoperiod,light intensity,turbidity and prey density on feed incidence and survival in first feeding yellow tang (Zebrasoma flavescens)(Bennett)

Zebrasoma flavescens (Bennett) aquaculture is limited by high mortality during first feeding. Photoperiod, light intensity, turbidity and prey density are culture parameters that have been shown to affect feed incidence and survival in some food fish species, offering a logical starting point to improve first feeding in Z. flavescens. This study aimed to determine the effect of photoperiod, light intensity, turbidity and prey density on feed incidence and survival in larval yellow tang age 3 DPH to 5 DPH (days post hatch). Larvae were reared in four photoperiods (24L:0D, 16L:8D, 12L:12D, 0L:24D), four light intensities (1,500, 3,000, 4,500 and 6,500 lx), three turbidity ranges (0 cells/ml, 100,000–200,000 cells/ml and 400,000–600,000 cells/ml) and four prey densities (1, 3, 6 and 9 per mL). Photoperiod at 16L:8D and 12L:12D significantly increased feed incidence; 16L:8D significantly increased survival. Light intensities at 3,000 and 4,500 lx significantly increased feed incidence. Larvae reared in 400,000–600,000 cells/ml fed and survived significantly better than those in clear water. Larvae in 1 per mL fed and survived significantly less than those fed at 6 per mL.     

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.     

Effect of light intensity and feed density on feeding behaviour,growth and survival of larval sablefish Anoplopoma fimbria

We studied the effects of light intensity on larval activity, feeding behaviour, growth and survival of a candidate species for aquaculture – sablefish (Anoplopoma fimbria). Of six light intensities ranging from 2 to 750 lux at the water surface, the greatest surviving biomass in small tanks was observed at 12–42 lux. In another experiment in larger tanks, behavioural observations showed that larvae fed poorly under light brighter than 800 lux but fed better at lower light intensities, depending on tank type. In a separate experiment, where live feed densities were varied between 2.5 and 17.5 rotifers per mL of tank water, surviving biomass and dry weight increased with higher feed densities. These experiments help refine methods for rearing larval sablefish by demonstrating effects of light intensity and feed density on larval performance.     

Reproductive performance of common dentex, Dentex dentex, broodstock held under different photoperiod and constant temperature conditions

The effect of photoperiod and temperature on the timing and the quality of spawning, and on associated endocrine changes in circulating 17β-oestradiol, 11-ketotestoserone (11-KT) and vitellogenin (Vtg) were investigated in common dentex, Dentex dentex, undergoing their second reproductive cycle. The possibility was also explored of using the measurement of steroids in the culture water of broodstock tanks, rather than in individual blood plasma samples, as a potentially useful tool for assessing the physiological state of a fish without disturbing them. One group of fish was exposed to a simulated natural seasonal cycle and ambient temperature (CONTROL). The other two groups were exposed to simulated seasonal photoperiod cycles (12 month-long) but which were phase-shifted either three months before (ADVANCED) or after (DELAYED) the natural cycle. Temperature was kept at 19.4±0.9 °C all-year-round. In the CONTROL, spawning started in mid-April and lasted until mid-June, while in the ADVANCED group, spawning started 4 months earlier and in the DELAYED group 2 months later than the CONTROL. The total egg production, egg quality, hatching rate, relative fecundity, and spawning index of the experimental groups were similar to the controls. The differences in spawning time induced by photothermal manipulation were associated with a difference in the timing of peak concentrations of plasma E₂, 11-KT and Vtg. In all three groups, the amounts of conjugated 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) and free and sulfated 11-KT which could be extracted from the water during the spawning period were significantly higher than those found in the preovulatory period. However, the differences were mostly less than 2-fold suggesting that, at least under the conditions employed in this study, the method was of limited use for non-intrusive detection of gonadogenesis and spawning (as had been hoped). The observed differences in spawning time and in the seasonal changes of sex steroids and Vtg confirm and extend the findings on marine fish. This revised version was published online in August 2006 with corrections to the Cover Date.     

The impact of light intensity and algal-induced turbidity on first-feeding Seriola lalandi larvae

Feeding performance (intensity and incidence) of first‐feeding yellowtail kingfish larvae was evaluated under a range of light intensities and algal‐induced turbidities. Larvae were fed with varying degrees of success under all light intensities tested (0–17 μmol s^?1 m^?2), in both clearwater and greenwater (8 × 10⁴ cells mL^?1). There was a consistent trend for feeding performance to increase with larval age and light intensity in both clearwater and greenwater conditions, demonstrating that visual proficiency increases with larval age. Feeding intensity remained low over the first 3 days of first feeding across all light intensities tested. Days 6 and 7 post‐hatch larvae showed considerably higher feeding intensities particularly at 8 and 17 μmol s^?1 m^?2. This improvement indicates an ontogenetic shift in sensory or locomotor competence. First‐feeding larvae performed equally well in both clearwater and greenwater (8 × 10⁴ cells mL^?1) conditions, although at the lowest light intensity tested (0.1 μmol s^?1 m^?2) feeding performance was noticeably reduced. Feeding performance was severely diminished across all larval ages at an algal cell density of 32 × 10⁴ cells mL^?1, demonstrating that for this species algal‐induced turbidities >16 × 10⁴ cells mL^?1 adversely affect the ability to capture free‐swimming prey during the first‐feeding window.     

The first‐feeding response of larval southern bluefin tuna,Thunnus maccoyii (Castelnau, 1872), and yellowtail kingfish,Seriola lalandi (Valenciennes, 1833), to prey density,prey size and larval density

We investigated the first‐feeding success of two species: southern bluefin tuna (Thunnus maccoyii) and yellowtail kingfish (Seriola lalandi) to determine if similar culture parameters can be used for both, especially when S. lalandi are held in the same tanks as prey for T. maccoyii. The feeding performance (proportion and intensity) was examined in three short‐duration (4 h) experiments: prey density, prey size and larval density. Increasing prey density from 0.5 to 25 rotifers mL^?1 increased the proportion of T. maccoyii and S. lalandi larvae feeding. Prey size alone did not affect feeding in either species. Seriola lalandi had a decreased proportion of larvae feeding when larval density reached 50 larvae L^?1 concurrent with a gradual increase in feeding intensity between 2 and 50 larvae L^?1. In T. maccoyii, there was no pattern to the effect of larval density on the proportion of larvae feeding. The overall feeding performance of larvae was higher in T. maccoyii than S. lalandi. Increased prey density improved the first‐feeding ability of T. maccoyii and S. lalandi larvae. The effect of larval density on S. lalandi feeding requires further investigation, to ensure that they remain feeding when provided as prey in T. maccoyii culture. The identification of factors in this study, which increase first‐feeding success, will improve the culture of both species.     

Effect of the photoperiod on the larval development,body growth and muscle cellularity of shi drum (Umbrina cirrosa L.)

Shi drum (Umbrina cirrosa L.) larvae were maintained under three photoperiod regimes: a natural photoperiod regime (16L:8D), continuous light (24L) and equal durations of light and dark (12L:12D) from the end of the vitelline phase to the end of the metamorphosis. Muscle and body parameters were studied at hatching and at 4, 10, 14, 39 and 55 days post hatching (dph). During the vitelline phase, the total body length growth was scarce, whereas the muscle grew significantly, being the hypertrophy of the main mechanism involved. Both the total body length and the hypertrophy were significantly greater at 16L:8D than in the rest of photoperiod regimes. At 10 and 14 dph, the greatest body length was reached at 16L:8D, followed by the 24L group, showing the 12L:12D group the lowest values. At 14 dph, the hypertrophy and hyperplasia were also higher at 16L:8D than in the rest of groups. At 39 dph, the highest values of body length were reached in both 16L:8D and 12L:12D regimes, this latter group reaching the highest values of hypertrophy, thus showing a compensatory growth when comparing with the previous stages. The end of the metamorphosis took place at 50–55 dph in all the groups, with 2.7–3.1 cm of body length (P > 0.05). At this stage, the transverse area of the white muscle was similar among the groups, but the greatest hypertrophy was reached at 16L:8D, whereas the highest hyperplasia was reached at 24L.     

Effect of diet and light regime on growth and survival of African catfish (Clarias gariepinus) larvae and early juveniles

Growth of larval sharptooth catfish Clarias gariepinus fed live Artemia nauplii , a specially prepared dry feed (MN-3), a commercial dry salmon starter feed (Silver Cup 3600), or a combination of 50% live Artemia and 50% MN-3, under conditions of either light or dark for 21 days was studied. For all diets, fish reared in darkened tanks were significantly larger than those in illuminated tanks from day 8 onwards. Fish fed a combination of live Artemia plus MN-3 grew significantly more quickly than those fed either live Artemia or MN-3 only. On day 21 of the experiment, average weight of fish fed the combined diet was 649 ± 30 mg (mean ± SEM ) in darkened tanks and 445 ± 16 mg in illuminated tanks, while those fed Artemia alone were 242 ± 9 and 198 ± 13 mg (dark and light, respectively) and fish fed MN-3 only were intermediate at 377 ± 20 and 267 ± 16 mg (dark and light, respectively). Catfish fed the salmon starter initially grew slowly, but after day 11 grew more quickly than the other groups. Mortalities were highest for fish fed salmon feed.
Permanent darkness enhances the growth of C. gariepinus larvae during and after metamorphosis. While dry diets promoted higher growth rate than live Artemia nauplii alone, a combination of the two resulted in the fastest growth.     

Effects of dietary arachidonic and eicosapentaenoic acids on common dentex (Dentex dentex Linnaeus 1758) larval performance

Oily emulsions containing constant levels of total fatty acids (FAs) and varying eicosapentaenoic acid (EPA) and arachidonic acid (ARA) levels were used to enrich rotifers. Common dentex larval survival and growth were compared between groups fed different enriched live prey. Growth, survival rate, and lipid composition of larvae suggest that feeding common dentex in the first 15 days posthatching with 2.5–3% EPA, 6–8% docosahexaenoic acid (DHA), and DHA/EPA ratio of 2.0–2.5 is sufficient to fulfill their EPA requirements. Higher amounts of dietary EPA did not result in any significant improvement in growth or survival. EPA requirement during this period of larval development does not seem to be as critical as other FAs during the first 15 days of common dentex larval development, but it does not exclude its essentiality later in development. In the case of ARA, nutritional requirements are low compared to other marine finfish species, with the upper limit of this essential FA being around 2% of total FAs provided in the live prey composition.     

Effects of culture conditions on feeding response of larval Pacific red snapper ( Lutjanus peru, Nichols & Murphy) at first feeding

Feeding incidence or number of larvae with preys (FIC) and intensity or number of prey per larvae (FIT) at first feeding of Pacific red snapper ( Lutjanus peru) larvae was investigated under different conditions: prey type (rotifer and copepod nauplius) and density, nauplii size, light intensity, water temperature, salinity and microalgae concentration. Rotifers were not consumed at any prey density and FIC increased significantly when a high nauplii density (10 > 1, 0.1 mL^?1) and light intensity (2000 > 1000, 500, 0 lx) were supplied. In a multifactorial experiment where light intensity (2000, 2500, 3000 lx), tank colour (grey and black) and prey type (nauplii and a mixed diet: rotifers and nauplii) were tested, a significant difference was found only for light intensity and prey type with a significant interaction between these factors. FIC was significantly higher with nauplii stage I–III than IV–VI and also at 25 °C than at 28 °C. Green water (0, 0.3 × 10⁶ or 1 × 10⁶ cells mL^?1) and salinity (25, 30, 35 gL^?1) did not affect FIC. FIT was not affected by any variables tested except in the density experiment where it was significantly higher at 10 nauplii mL^?1.     

Growth and survival of Arcto-Norwegian and Norwegian coastal cod larvae (Gadus morhua L.) reared together in mesocosms under different light regimes

To evaluate genetic differences in growth and survival potential as a function of light regime, cod larvae from two stocks (CC: coastal cod and AC: Arcto-Norwegian cod, spawning at latitudes of 60°N and 69°N respectively) were co-reared in mesocosms. The experiment was carried out with two artificially illuminated light regimes, corresponding to the natural photoperiod at peak spawning of the respective stocks (CC: 7–8 h distinct dark period, AC: ‘mid-night sun’ as continuous light with 2–3 h reduced light intensity). One additional regime with ambient natural light analogous to 60°N was used. At termination on day 36 post-hatch, larvae of the co-reared stocks were distinguished from each other by a genetic marker in the CC stock. Stock-specific differences in growth rate and survival were indicated, with CC larvae growing and surviving better than AC larvae. This is in agreement with earlier comparisons of larval growth in these stocks. The 69°N light regime did not enhance growth for any of the two stocks. However, natural light greatly increased growth rate of both stocks, indicat ing important mechanisms in regulation of larval feeding relative to light quality or intensity. The results may be important for choice of stock and illumination in intensive aquaculture of this species.     

Effect of light intensity,prey density,and ontogeny on foraging success and prey selection of larval yellow perch (Perca flavescens)

Light intensity has been shown to influence the foraging success of larval fish. However, the effect of light intensity on larval foraging is likely variable and influenced by both the density and characteristics of planktonic prey. In this study we examined the influence of light intensity of 0.1, 2.0, and 60 μmol·s^?1·m^?2 Photosynthetically Active Radiation (PAR) on foraging of yellow perch (Perca flavescens) larvae at two prey densities. We fed them with a mixture of zooplankton taxa common to lakes inhabited by yellow perch. In addition to light intensity and prey density, the effect of larval yellow perch size was examined by using fish ranging from 9 to 15 mm. The results of our study indicated that yellow perch larvae are well adapted to feed at a wide range of light intensities, as there was no difference in foraging success at investigated light intensities. Increasing prey density from 25 to 150 (zooplankton·l^?1) significantly improved the foraging success of larval yellow perch. However, the influence of prey density on foraging success was dependent on fish length. Improved foraging success at increased prey densities occurred only for individuals with a total length >10 mm. Overall, prey selection by fish larvae was influenced by light intensity, prey density, and fish length. However, the factors that influenced selection for specific prey types differed. Our study, combined with evidence from other field and laboratory work, highlight the need for a better understanding of the influence of prey density on foraging throughout ontogeny.     

光环境因子对循环水养殖系统中大西洋鲑生长和摄食的影响

采用正交实验法,研究了不同光色(白光,A1;蓝光,A2;红光,A3)、光周期(24L︰0D,B1;12L︰12D,B2;8L︰16D,B3)和光强(0.88 W/m2,C1;4.55 W/m2,C2;8.60 W/m2,C3)对循环水养殖系统中体质量(850.97±82.77)g的大西洋鲑(Salmo salar)生长和摄食的影响。实验设A1B1C1(1)、A1B2C2(2)、A1B3C3(3)、A2B1C2(4)、A2B2C3(5)、A2B3C1(6)、A3B1C3(7)、A3B2C1(8)、A3B3C2(9)9个处理组,在相应设定条件下饲养180 d。结果表明,在光色为红光、光周期为12L︰12D和光强8.60 W/m2条件下大西洋鲑的成活率最高,但光色、光周期和光强对成活率的影响差异不显著(P0.05);实验期间各组鱼的相对增重率和肥满度差异均不显著(P0.05);至第120天,2、5、6组鱼的体长特定生长率显著高于1组(P0.05);至第180天,1、2、4、7、8组鱼的体质量特定生长率显著高于6组(P0.05),1、2、3、4、7、8、9组鱼的日增重显著高于6组(P0.05),9组鱼的体质量变异系数显著低于7组(P0.05)。9组鱼血浆中生长激素显著高于1、2、3、4、6、7和8组(P0.05);摄食率、饲料转化效率和饲料系数最佳时的光照条件为:红光、12L︰12D、8.60 W/m2,但光色、光周期和光强对摄食率、饲料转化效率及饲料系数的影响差异不显著(P0.05)。本实验条件下,较为适宜的光照条件是:红光、12L:12D、8.60 W/m2。     

Effects of stocking density and feeding levels on growth and feed efficiency of Nile tilapia (Oreochromis niloticus L.) fry

The effects of stocking density and feeding levels on larval survival, growth rates, feed utilization efficiency and body composition of Nile tilapia (Oreochromis niloticus L.) fry were investigated in two consecutive experiments. In experiment 1, swimup fry (0.016 g average body weight) were stocked in 20‐L fibreglass tanks, in a closed, recirculating indoor system, at five stocking densities (3, 5, 10, 15 and 20 fry L^?1) and fed a larval test diet (40% crude protein) to apparent satiation, three times a day, for 40 days. Fish survival, percentage weight gain and specific growth rate (% SGR) were negatively correlated with stocking density. The best performance was achieved at 3 fry L^?1. However, no significant differences in growth parameters were found between 3 and 5 fry L^?1. Body composition was not significantly affected by stocking density. In experiment 2, fry (0.016 g average body weight) were stocked at 5 fry L^?1, and fed a larval test diet (40% crude protein) at six feeding levels (10%, 20%, 25%, 30% and 35% BW day^?1) and to satiation, three times a day for 40 days. Fish growth rates and survival were extremely poor at 10% feeding level, and improved significantly with increasing feeding levels up to 30%, and levelled off with further increase in feeding levels. On the contrary, feed conversion ratio (FCR) and protein production value (PPV) were negatively correlated with feeding level. The lowest feeding level (10%) produced significantly lower body lipid and higher protein and ash than other feeding levels. The present results suggest that the optimum stocking density and feeding level of Nile tilapia fry are 5 fry L^?1 and 30% per day respectively.     

Effect of stocking density and feeding regime on larval growth,survival, and larval development of Japanese flounder,Paralichthys olivaceus,using live feeds

This research examined the effect of initial stocking density and feeding regime on larval growth and survival of Japanese flounder, Paralichthys olivaceus. Larval rearing trials were conducted in nine 50‐L tanks with different initial stocking densities combined with different feed rations (20 larvae/L with standard feed ration [LD], 80 larvae/L with standard feed ration [HD], and 80 larvae/L with four times the standard feed ration [HD+]). Larvae were stocked on 0 days posthatch (DPH) following hatching of the fertilized embryos. Larval total length (TL), survival rates, and final densities were observed on larval settlement (32 DPH) to evaluate larval rearing performance. At 32 DPH, there were no significant differences (p > .05) in TL or survival rates between the LD (46.5 ± 17.0%) and HD+ (40.3 ± 9.4%). The TL and survival rate of HD (23.1 ± 3.5%) were significantly lower than that of LD and HD+ (p < .05). However, the larval density of HD was significantly higher than that of LD (p < .05). HD+ achieved the best larvae production (32.27 ± 7.51 larvae/L), supported by sufficient food source, high water exchange, and proper water quality management (routine siphoning, surface skimming). The larval‐rearing protocols and larval development from hatching to metamorphosis is described in detail, with corresponding photographs taken during the experiment.