Effect of Photoperiod Manipulation on Growth Performance,Physiological and Hematological Indices in Juvenile Persian Sturgeon,Acipenser persicus

The effect of five different light regimes on growth, stress and hematological indices was studied in Persian sturgeon, Acipenser persicus. Fish with average weight of 645.3 ± 11.2 g were subjected to different photoperiods (24 L, 12 L:12 D, 16 L:8 D, 8 L:16 D and 24 D) for 8 wk. Blood samples were collected at the end of the experiment for measuring cortisol, glucose and hematological features. The whole growth parameters showed no significant difference. Plasma cortisol concentration was significantly higher in 12 L:12 D, while the lowest level was observed in fish exposed to 24 D. No significant changes were observed among the treatments for glucose concentration. Lactate concentration varied significantly among the treatments. Some hematological indices including hematocrit and number of white blood cells were affected by different light regimes, but the others (hemoglobin and number of red blood cells) were not affected significantly. The results showed that photoperiod manipulation can alters some stress‐related metabolites and may enhance growth rate in fish exposing to continuous darkness.     

Reproduction,growth and stress response in adult red sea bream,Pagrus major (Temminck & Schlegel) exposed to different photoperiods at spawning season

Adult red sea bream, Pagrus major (body weight, 1.0–2.0 kg) was exposed to three photoperiods [12 h light:12 h dark (12L:12D), 16 h light:8 h dark (16L:8D) and 24 h light:0 h dark (24L:0D)] from 2 months before spawning till the end of the spawning season to investigate growth, spawning and stress response. During the spawning season, tanks were checked every morning for spawned eggs. The growth performance in fish under 24L:0D was stimulated with significantly higher feed intake than those under other photoperiods (P<0.05). The number of eggs and gonadal histology confirmed that three and five females out of six in each of duplicate tanks of the 16L:8D treatment spawned. In contrast, only two out of six females in one tank of the 24L:0D treatment spawned, and no spawns were observed in the 12L:12D treatment. At the end of the spawning period, both 17β‐estradiol and testosterone levels were significantly higher in fish exposed to 16L:8D followed by 12L:12D and 24L:0D photoperiods (P<0.05). Photoperiod manipulation did not cause significant stress response in fish (P>0.05). The results suggest that stimulating the growth performance of red sea bream at reproductive stage with a 24L:0D photoperiod is possible if the fish are subjected to this photoperiod long before the onset of the spawning season.     

Stimulation of growth performance without causing stress response in young red sea bream, Pagrus major (Temminck & Schlegel), by photoperiod manipulation

Three photoperiods (12L:12D, 16L:8D and 24L:0D) were used to investigate the growth performance and stress response in red sea bream, Pagrus major (body weight 200–400 g). Fish were fed a commercial diet to apparent satiation, two times a day for 8 weeks. Fish exposed to a 24L:0D photoperiod showed a significantly higher weight gain (%) than those exposed to other photoperiods (P<0.05). The best specific growth rate and feed conversion efficiency were achieved at 24L:0D and 16L:8D, without significant differences among them. Although fish exposed to 16L:8D showed a significantly higher plasma level of cortisol than those exposed to other photoperiods in the third week, there was no major variation in the cortisol level among the treatments either at the sixth week or at the end of this study. There were no significant differences either in the haematocrit level or the plasma levels of glucose, total cholesterol and total protein among the treatments during this study. The results revealed that the growth performance of red sea bream reared from 200 to 400 g can be stimulated significantly using a continuous (24L:0D) photoperiod without any measurable significant stress response in fish.     

Growth performance and physiological responses in striped knifejaw, Oplegnathus fasciatus, held under different photoperiods

The growth performance and stress response in striped knifejaw, Oplegnathus fasciatus (body weight 100–300 g) reared under four photoperiods (6L:6D, 12L:12D, 16L:8D and 24L:0D) were investigated. Fish were fed a commercial diet to apparent satiation, two times a day for 8 weeks. A trial of acute handling and confinement stress was also carried out to investigate the stress-induced levels of different stress indicators in O. fasciatus. Blood was also collected from undisturbed fish which was considered as control. Although there were no significant differences in weight gain, specific growth rate (SGR) and feed conversion efficiency (FCE) in fish exposed to 6L:6D, 16L:8D and 24L:0D photoperiods, all parameters in these photoperiods were significantly higher than those of 12L:12D photoperiod (P < 0.05). There was no significant difference in protein retention efficiency (PRE) between fish exposed to 16L:8D and 24L:0D photoperiods, but PRE in both photoperiods was significantly higher than that of 12L:12D photoperiod.Acute stress significantly increased the plasma levels of cortisol (110.3 ng ml^− 1) and glucose (195.4 mg dl^− 1), and decreased plasma levels of total protein (0.8 g dl^− 1); however, all parameters were returned back to the levels indistinguishable from those of control, undisturbed fish within 24 h. The levels of cortisol, glucose and total protein in fish exposed to different photoperiods during the study were far from the stress-induced levels (P < 0.05). The results demonstrated that the growth performance of O. fasciatus reared from 100 to 300 g can be stimulated significantly by using the manipulated photoperiods where feeding time may be playing an important role to increase food intake and feed conversion efficiency. It also revealed that the artificial photoperiods did not cause significant stress response in fish.     

Influence of water management,photoperiod and aeration on growth,survival, and early spat settlement of the hatchery-reared green mussel,Perna viridis

In an attempt to induce early spat settlement and improve mussel seed production, this study aims to determine the influence of water management, photoperiod, and aeration, on the growth, survival and settlement of green mussel (Perna viridis). Water in the pediveliger rearing tanks was changed every day, every 3 days and every 5 days for the water-management experiment. Pediveligers were exposed in 24L:0D h (light: dark), 12L:12D h and 0L:24D h conditions for the photoperiod experiment. Three aeration intensities were also tested—mild (10 L h−1), moderate (20 L h−1), and strong (30 L h−1). This study demonstrated that changing water every 3 days was effective in maintaining the rearing water quality and improving the growth and survival of P. viridis larvae. Highest growth and survival rates were observed in P. viridis spats grown in 0L:24D h photoperiod. There was no significant difference in the settlement rate of larvae exposed to different photoperiods. Mild aeration has shown to improve the growth of P. viridis larvae, but higher survival and settlement rates were attained in the strongly-aerated conditions. Therefore, when the larvae start to settle, it is recommended to expose them to darkness, change the water every 3 days and provide a strong aeration to be able to attain high survival and settlement rates, and bigger spats.     

Photoperiod influences the growth, food intake, feed efficiency and digestibility of red sea bream (Pagrus major)

Two consecutive trials were conducted to investigate the effects of photoperiod manipulation on growth rate, food intake and feed conversion efficiency (Trial 1), and the digestibility of nutrients and energy (Trial 2) in red sea bream, Pagrus major (body weight 19–120 g). Fish were exposed to four photoperiods (6L:6D, 12L:12D, 16L:8D and 24L:0D) with light intensity 1500 lx on the water surface. The fish were fed with a commercial diet to apparent satiation. In Trial 2, 0.5% chromic oxide (Cr₂O₃) was used as an inert marker. Significantly higher weight gain and specific growth rates were observed in fish exposed to a 24L:0D photoperiod followed by 16L:8D, 6L:6D and 12L:12D photoperiods (P < 0.05). Food intake and feed conversion efficiency (FCE) were also significantly higher in fish exposed to 24L:0D followed by 16L:8D, 6L:6D and 12L:12D photoperiods (P < 0.05). Fish exposed to 24L:0D and 16L:8D photoperiods showed significantly higher lipid and energy digestibility than those exposed to a 12L:12D photoperiod (P < 0.05). The results demonstrated that the enhancement of growth performances under 16L:8D and 24L:0D photoperiods were attributed to improved appetite, greater food intake and higher feed conversion efficiency as well as higher digestibility.     

Growth and age at first maturity in turbot and halibut reared under different photoperiods

The effect of extended photoperiods on growth and age at first maturity was investigated in 166 (79 females and 87 males) individually tagged Atlantic halibut Hippoglossus hippoglossus and in 114 (50 females and 64 males) individually tagged turbot Scophthalmus maximus. The halibut were reared at 11 °C on four different light regimes from 10 February to 6 July 1996: simulated natural photoperiod, (LDN), continuous light (LD24:0), constant 8 h light and 16 h darkness (LD8:16) and LD8:16 switched to continuous light 4 May 1996 (LD8:16–24:0). From 6 July 1996 to 9 February 1998 the LD24:0 and LD8:16–24:0 were reared together under continuous light and the LDN and LD8:16 together under natural photoperiod. The turbot were reared at 16 °C on three different light regimes: constant light (LD24:0), 16 h light:8 h darkness (LD16:8), or simulated natural photoperiod (LDN). After 6 months on the different photoperiods, the turbot was reared together on LDN for approximately 12 months until first maturation. Juveniles subjected to continuous light (halibut) or extended photoperiods (halibut and turbot) exhibited faster growth than those experiencing a natural photoperiod or a constant short day. Moreover, when the photoperiod increased naturally with day-length or when fish were abruptly switched from being reared on short-day conditions to continuous light, a subsequent increase in growth rate was observed. This growth enhancing effect of extended photoperiods was more apparent on a short time scale in Atlantic halibut than in turbot, but both species show significant long-term effects of extended photoperiods in the form of enhanced growth. In both species lower maturation of males was seen in groups exposed to extended or continuous light compared to LDN and this could be used to reduce precocious maturation in males leading to overall increase in somatic growth. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of photoperiod on egg production and hatching success, naupliar and copepodite development, adult sex ratio and life expectancy of the tropical calanoid copepod Acartia sinjiensis

The tropical calanoid copepod Acartia sinjiensis has good potential for mass culture as live feed for reef fish larvae. The present study was conducted to evaluate the effects of photoperiod on various parameters related to A. sinjiensis productivity in culture.Five photoperiods of Light:Dark = 0:24; 6:18; 12:12; 18:6 and 24:0h were setup. Daily egg production of individual females under each photoperiod was monitored for 8 consecutive days. The females were randomly selected daily from stock cultures kept under respective photoperiods and discarded after experiment. The results showed a clear trend of increasing egg production with longer illumination period. Under constant darkness, acclimatization was evident as egg output increased steadily over the 8 day period. Statistics showed that photoperiod significantly (p < 0.005) affected mean daily egg production, with the highest egg output recorded at 18L:6D and 24L:0D (17.6 ± 1.7 and 17.6 ± 1.8 eggs/female/day respectively), which were significantly higher than all other treatments. Photoperiod also significantly affected 48 h egg hatching success (p < 0.005), a trend of increased hatching success with longer light phase was demonstrated. The highest hatching rate (87.2 ± 1.4%) was recorded at 24L:0D, which was significantly higher than the 0L:24D and 6L:18D treatments but not significantly different from the second highest (85.3 ± 2.6%) hatching rate of 18L:6D treatment.Photoperiod was further confirmed to significantly (p < 0.005) affected naupliar and copepodite development with accelerated development observed with increased illumination period of photoperiods. Mean development time from egg to adult was the shortest at 6.00 ± 0.33 days under constant light (24L:0D), followed by 6.24 ± 0.24 days at 18L:6D, both were significantly shorter than that of 0L:24D and 6L:18D treatments although no significantly difference was detected between themselves. Adult life expectancy was also found significantly (p < 0.005) affected by photoperiod with the shortest adult life span recorded under constant light (24L:0D) (9.4 ± 0.4 days), which was significantly shorter than all other photoperiods tested. Adult sex ratio was the only parameter tested that was not significantly affected by photoperiod, a skewed sex ratio in favor of female was found across all photoperiod treatments.Based on results of current study, it is recommended that a photoperiod of 18L:6D being adopted for A. sinjiensis culture to maximize its productivity for aquaculture hatcheries.     

Feeding interval and photoperiod influence the growth performance of striped knifejaw,Oplegnathus fasciatus

A two‐factor experiment incorporating two photoperiods (16 L:8 D and 24 L:0 D) and four feeding intervals (6, 9, 12 and 24 h) was carried out to determine the most efficient feeding interval and photoperiod for striped knifejaw, Oplegnathus fasciatus. Fish were fed a commercial diet to apparent satiation for 10 weeks. Blood was collected to measure the stress indicators. Both the photoperiod and the feeding intervals had a significant effect on the growth performance of striped knifejaw; however, their interaction did not produce any significant effect. The final body weight, weight gain (%) and feed intake at 6‐, 9‐ and 12‐h feeding intervals under 16 L:8 D were significantly higher than those at the 24‐h interval irrespective of the photoperiod (P<0.05). The specific growth rate at 6, 9 and 12 h intervals of the 16 L:8 D photoperiod was significantly higher than that of the other feeding intervals, except at 12 h of the 24 L:0 D photoperiod (P<0.05). At the end of the experiment, there were no significant differences in the plasma levels of cortisol, glucose and total protein observed in fish exposed to different photoperiods compared with the initial levels. The results suggested that a combination of a 16 L:8 D photoperiod and either of 6‐, 9‐ or 12‐h intervals can be used to stimulate the growth performance in striped knifejaw.     

Effects of photoperiod on growth and spawning efficiency of Nile tilapia (Oreochromis niloticus L.) broodstock in a recycling system

This study was conducted to evaluate the effects of photoperiod on the growth, feed conversion ratio (FCR) and spawning performance of Nile tilapia (Oreochromis niloticus) broodstock. Duplicate groups of two males (66±3.04 g) and six females (50.5±1.58 g) were stocked in 0.4 m³ fibreglass tanks in a recirculating water system at a male:female ratio of 1:3. The fish were subjected to four photoperiod treatments: 24:0 light:dark (L:D), 18L:6D, 12L:12D and 6L:18D. Light intensity was kept constant at about 2500 lx throughout the study. The fish were fed a commercial tilapia diet (35% crude protein and 16.6 MJ GE kg⁻¹) at a daily rate of 2–3% of tank biomass, twice a day, for 130 days. Males grew significantly faster than females under all photoperiod regimes. The best growth rate and FCR were attained at 18L:6D, followed by 24L:0D, 12L:12D and 6L:18D respectively. The number of eggs per female, number of eggs per spawn and number of spawnings per female were all significantly higher in the 12L:12D treatment than in all other photoperiod cycles. Interspawning intervals and days elapsed per spawn were also shorter in the 12L:12D treatment. The time to first spawning was slightly longer in the 24L:0D and 6L:18D than in 12L:12D and 18L:6D light phases. The 18L:6D and 6L:18D photoperiods produced the lowest spawning performance. It is concluded that a 12L:12D photoperiod regime should be adopted for maximum fecundity, seed production and spawning frequencies of Nile tilapia broodstock reared in intensive, recirculating systems. If maximum reproduction is desired, a near‐natural day length photoperiod should be used.     

Effects of different photoperiods on growth, stress and haematological parameters in juvenile great sturgeon Huso huso

The effects of constant light (24L:00D), no light (00L:24D) and two light–dark periods (18L:06D;12L:12D) on the growth, stress and haematological variables were assessed in juvenile great sturgeon, Huso huso . During the 8-week experimental period, juveniles (22.5 ± 0.6 g) were kept under a 150 lx light intensity in fibreglass tanks (0.8 m², 500 L). Differences in growth were insignificant during the experiment, but lactate levels were higher in the 00L:24D and 24L:00D photoperiods compared with 12L:12D and 18L:06D photoperiods. Cortisol levels did not show differences among the various photoperiods. At the end of the experimental period, fish reared under a 12L:12D photoperiod had higher haemoglobin values and erythrocyte numbers than in the other photoperiods, while no differences were found between groups with regard to haematocrit values or leucocyte numbers. The highest survival rate (89%) was observed in the 12L:12D period in which the levels of lactate and cortisol as stress indicators were minimal. The results indicate that various photoperiods cause different stress levels in juvenile great sturgeon and have no significant effects on growth, at least in short time periods.     

The effect of photoperiod on growth, survival, colour and activity of juvenile southern rock lobster, Jasus edwardsii

Juvenile (1–10 g) southern rock lobsters, Jasus edwardsii, were subjected to five photoperiods [0L(light):24D(dark); 6L:18D; 12L:12D; 18L:6D; 24L:0D] during a 112‐day trial, and growth, survival, colour, food consumption and activity were examined. Lobsters grown under the 6L:18D and 24L:0D photoperiods had significantly lower (P < 0.05) final mean weight and specific growth rate than any other treatments. Photoperiod had no effect on survival or colour of lobsters. Food consumption differed significantly during the first week of the trial; after 5 weeks, food consumption was similar in all treatments. Major peaks in activity occurred during dark periods for lobsters exposed to photoperiods that had a light:dark regime. Activity of lobsters exposed to continuous light or dark regimes remained constant and at low levels during the 24‐h period. Food consumption or activity does not appear to determine the rate of growth of lobsters in the different photoregimes. One over‐riding outcome of this and other studies on photoperiod is that the growth and survival response of juvenile J. edwardsii was not significantly better than those of the standard 12L:12D cycle.     

艾比湖卤虫滞育诱导的临界光周期和感知光照度的研究

卤虫具有滞育模式(卵生)和非滞育模式(卵胎生)两种繁殖模式,而光周期可能是影响其繁殖模式的重要的环境因子,因此明确其临界光周期和感知光照度对于有效地调控卤虫滞育、繁殖等将具有重要实践意义。本研究在实验室条件下研究了艾比湖卤虫的临界光周期和感知光照度,结果表明,在常规养殖盐度(80)和温度(25℃)条件下,艾比湖卤虫的光反应曲线与典型的长日照反应型滞育昆虫类似,在非极端光周期下,艾比湖卤虫的临界光暗时长为(8.38±0.37)h,相应的临界日长为15.62h;在极端光周期下,24h光暗时长,滞育率为(32.42±6.70)%,极显著低于邻近长光暗时长滞育率(P0.01);0h光暗时长,滞育率为(19.01±5.98)%,较邻近短光暗时长滞育率略高,但差异不显著(P0.05)。感知光照度试验表明,艾比湖卤虫感知光照度可能处于10~50lx。本研究为卤虫的滞育诱导和繁殖模式的光控化养殖提供了重要的科学基础。     

Enhanced growth and retarded gonadal development of farmed rainbow trout,Oncorhynchus mykiss (Walbaum) following a long‐day photoperiod

Long‐day photoperiods are considered as an effective managerial tool in manipulating of reproduction and somatic growth in a number of fish species. In this study, the effects of three different artificial photoperiods on the gonadal development and somatic growth of rainbow trout (Oncorhynchus mykiss L.) were investigated. Two years‐old immature female rainbow trout (279.94 ±2.25 g) were exposed to three artificial photoperiod regimes of 24L:0D, 18L:6D and 6L:18D and natural light (NL) regime for 5 months. The highest gonadosomatic indices were recorded in NL and 6L:18D groups while the rates were significantly lower in fish maintained under 18L:6D and 24L:0D photoperiods (P < 0.05). Mean oocyte diameters in fish exposed to 24L:0D and also to 18L:6D were significantly lower than the 6L:18D and NL groups. Photoperiods with 24L:0D and 18L:6D regimes resulted in significantly higher mean final weights and specific growth rates (SGR) than NL regime. The highest mean final weight (635.45 ± 16.19 g) and SGR (1.03 ± 0.04% day^?1) were obtained under 24L:0D photoperiod. Fish exposed to 24L:0D and 18L:6D showed the highest condition factor as 1.44 ± 0.01 and 1.44 ± 0.02 respectively, when compared with the NL (1.27 ± 0.01) and 6L:18D (1.34 ± 0.02) groups. Basically, the results suggested that continuous artificial lightning can be used as an influential factor in delaying gonadal development and enhancing somatic growth in rainbow trout during gonadal growth phase.     

Somatic growth, survival, feed utilization and starvation in European elver Anguilla anguilla (Linnaeus) under two different photoperiods

The aim of the study was to determine the effect of two photoperiod regimes under artificial conditions on growth performance and survival in the European eel Anguilla anguilla during the transition from glass eel to elver. The fish were held in 12-h-light:12-h-dark (12L:12D) and in continuous darkness (DD) in fed and fast trials lasting 80 days. Fed fish kept in the dark showed higher somatic growth, and a better feed conversion ratio, higher protein and lipid content, with significant differences between treatments. Dark environment increased the survival rate in comparison with fish exposed to 12L:12D, during which eels showed lower survival rates and greater variations in size. Fasted fish suffered loss of body mass in both photoperiods at the end of the experimental phase, but fish exposed to 12L:12D lost more body mass. These results indicate that the photoperiod is a key factor during the glass eel–elver stage, which may contribute to optimizing the early stages of eel culture.     

Optimal temperature and photoperiod for the spawning of blue crab,Callinectes sapidus,in captivity

Like all poikilotherms, the growth and reproduction of blue crab, Callinectes sapidus depends on temperature and season. Warmer water temperatures in the Chesapeake Bay allow for ovarian development and spawning, while colder water temperatures slow their metabolism and reproduction. The current study aimed to identify optimal environmental conditions for inducing reproduction in animals held in long‐term captivity for year round production in aquaculture through environmental manipulations. Temperature and photoperiod were the main environmental factors tested for 25 weeks: 11°C and 21°C, with the following photoperiods: 0L:24D, 8L:16D, 16L:8D and 24L:0D. At 21°C, the females increased spawning frequency, which was arrested at 11°C. Shorter light exposure at 21°C increased spawning frequency, while constant light inhibited and did not produce spawning. Constant dark (0L:24D) at 21°C produced the most (86%) spawns, but yielded poor larval quality. At 21°C with all photoperiod conditions except constant light, the first spawning took 94.8 ± 32.4 days to occur (n = 17). With females producing multiple spawns, the intervals between the first and second spawns and the second and third spawns were 37.7 ± 8.7 days (n = 6) and 31.0 ± 7.1 days (n = 2) respectively. Analysis of our data using response surface methodology (RSM) predicts the following conditions: at 15–19°C and 0–10 hr darkness for maximal survival and at 19–22°C and 0–8 hr darkness for spawning. The number of larvae produced was positively correlated with size (weight) of the female C. sapidus, suggesting the importance of female size in reproduction.     

Larval survival,development and growth in the horsehair crab,Erimacrus isenbeckii,cultured under different photoperiod conditions

Larval sinking causes larval mass mortality during seed production in the horsehair crab, Erimacrus isenbeckii. Under normal light conditions, horsehair crab larvae generally show negative phototactic behaviour and sink in their rearing seawater. It has been proposed that culturing larvae in the dark may prevent larval sinking. Herein, we examined the effect of photoperiods on horsehair crab larval survival and development to facilitate the development of larval rearing techniques that prevent sinking. Newly hatched larvae were reared with Artemia to the first crab stage in 2‐L beakers under five photoperiods: 0L:24D, 6L:18D, 12L:12D, 18L:6D and 24L:0D. Larvae survived and molted to the first crab stage under all tested photoperiod conditions. The survival rate improved with increasing light period, whereas the developmental period for each larval stage decreased with increasing light period. Longer light periods increased the carapace length at the first crab stage. Our results suggest that larvae could be cultured to the first crab stage in large‐scale tanks under constant darkness. However, significantly improved larval performance under longer photoperiodic conditions indicates a need for developing alternative culture techniques to control larval behaviour in the seed production tank.     

Effect of photoperiod and tank colour on growth and survival of pelagic‐phase seahorse Hippocampus reidi

The effect of photoperiod and tank colour on the survival and growth of juvenile seahorse Hippocampus reidi was investigated in the first 15 days after release (DAR). In the first experiment, newly released seahorses were exposed to six photoperiods – 6 h of light (L):18 h of darkness (D), 10L:14D, 12L:12D, 14L:10D, 18L:6D and 24L:0D. In the second experiment, juveniles were kept in tanks of different background colours – blue, white, black, clear and red. No significant differences were observed in the growth and survival among seahorse subjected to 10–24 h of light (P > 0.05). At the end of 15 DAR, fish exposed to 6L:18D showed lower growth in height and weight compared to other treatments (13.8 mm vs. 20.0–22.2 mm and 13.4 mg vs. 37.2–43.2 mg respectively) and lower survival (80% vs. 88–95% respectively). Tank colour did not affect growth and survival of juveniles up to 15 DAR.     

Photoperiod affects the survival rate but not the development of larval swimming crab Portunus trituberculatus

Photoperiod is a crucial environmental factor affecting the survival and development of crustacean larvae. The full-spectrum light-emitting diodes (LEDs) were used as light sources to investigate the effect of five photoperiods, i.e., 0 L:24D (constant darkness), 6 L:18D (6 h photophase), 12 L:12D (12 h photophase), 18 L:6D (18 h photophase), and 24 L:0D (constant light) on the survival and development of the swimming crab Portunus trituberculatus larvae (from zoea I to juvenile crab). Natural photoperiod (ambient) was used as a control group. Each treatment had four replicates (n?=?4, 100 larvae per replicate). The experiment lasted 20 days when all the larvae died or metamorphosed into juvenile crabs. The results revealed that the P. trituberculatus could not metamorphose into juvenile crab under constant darkness, 6 h photophase, and constant light, and all the larvae died in zoeal III, zoeal IV, and zoeal IV stage, respectively. The highest survival and the shortest developmental duration of larvae were found in the 12 h photophase group (1.75%, 16.80 d) but were not statistically different from those reared in the 18 h photophase group (0.75%, 17.00 d) and natural photoperiod (0.25%, 18.90 d). The above results indicated that full-spectrum LEDs could be a considerable alternation for natural light, and the optimal photoperiod for P. trituberculatus larvae is 12–18 h photophase.

     

Effects of photoperiod on growth performance and melanogenesis pathway for skin pigmentation of Malaysian red tilapia

Farming of red tilapia is increasing rapidly. However, its commercial farming development is challenged by lack of clear information on genetic basis for skin colour and pigmentation differences due to environmental changes. This study investigated the effects of photoperiod (light:dark, L:D) on the growth and skin colour variation of Malaysian red tilapia. A total of 180 fish weighing 150.48 ± 0.44 g were reared under natural photoperiod (13L:11D, control), prolonged lightness (24L:0D) and prolonged darkness (0L:24D) in three replicates for 78 days. The weight gain of fish cultured under both prolonged light and darkness were significantly higher than fish under natural photoperiod. The tyrosinase level in ventral skin was significantly higher for fish cultured under prolonged darkness condition than in the other two photoperiod regimes. Contrary, the cysteine level in the dorsal skin was significantly higher in the fish cultured under natural photoperiod than in prolonged light and darkness. The relative mRNA expressions of SRY‐related HMG‐Box 10 (sox 10), tyrosine (tyr), tyrosine‐related protein 1 (tyrp‐1) and solute carrier family 7 member 11 (slc7a11) genes were significantly higher in ventral skin of fish under prolonged darkness than the other two photoperiods. This study demonstrates that photoperiod has an impact on melanogenesis and growth of red tilapia. Understanding the effects of photoperiod on genetic basis of red tilapia will help in selective breeding programme of the important economic traits for the development of commercial red tilapia farming.