Continuous Illumination at Increasing Light Intensities and the Effects on the Growth and Survival Snubnose Pompano Trachinotus Blochii in the Early Stage

The study investigated the influence of continuous illumination at increasing light intensities on feeding, growth, and survival of early-stage snubnose pompano larvae from 1 to 10 days post-hatching (DPH). Fish larvae were exposed to 5 treatments with 3 replicates [T1 – natural indoor light; 12 hours light (hL): 12 hours dark (hD), T 2 – 300-500 lux (lx), T 3 – 300-1000 lx, T 4 – 300-2000 lx, T 5 – 300-3000 lx]. Newly hatched larvae were stocked at 15 ind. /L density and fed with enriched rotifers (Brachionus plicatilis; 50-250 µm) at 30 ind. /ml starting from 2 DPH. The number of rotifers in the digestive organ, feeding incidence, and total length of larvae were examined at 3-hour intervals from 0400 hour (H) to 2200H on 3 DPH, at 6-hour intervals from 4 to 5 DPH, and once on 8 DPH at 1000H. The fish's final growth and survival were determined after the study. Results justified that snubnose pompano is a visual feeder and exhibits diel rhythm within 24 hours of light, while larvae at natural photoperiod usually undergo diurnal rhythms. However, changing light intensity conditions from low to high levels altered the feeding behavior of the fish larvae. Better and consistent feeding and survival of larvae were obtained at moderate continuous illumination at increasing light intensities (300-500 lx), but more remarkable fish growth can be obtained at higher light treatments (300-1000 lx, 300-2000 lx, 300-3000 lx). Adverse effects of higher light intensities on larvae survival were observed after 5 DPH.


Introduction
The snubnose pompano Trachinotus blochii is among the promising aquaculture species (Mapunda et al., 2021) and has good marketing prospects in the Asia Pacific region with a high economic value  (Haryanto et al., 2021).Pompano aquaculture is believed to be the next big thing in the Philippines, and there has been an increasing demand in the domestic and export markets.However, the supply of T. blochii fingerlings for aquaculture is problematic due to the low survival in the hatchery phase (Mapunda et al., 2021), resulting in a lack of fingerlings to stock into cages and ponds, a bottleneck for increasing its global output (Mapunda et al., 2021).
The interaction of environmental factors experienced during early life and intrinsic traits inherited from the parents drives fish development (Kamler, 2005).Light is one of the main environmental factors influencing many aspects of animal life (Ruchin, 2021).Studies have proven light to alter prey identification, feeding ecology, and fish larvae development (Mapunda et al., 2021).For T. blochii, its early-stage larvae are particularly receptive to applying an artificial light system and extended day length (photoperiod), improving the fish's growth and survival (Alejos & Serrano Jr., 2018).
In the natural environment, the behavioral development of pompano larvae includes a phase of being pelagic, alternately settling to the bottom and swimming up, and becoming benthic after transformation (Berry & Iverson, 1967).According to Sumpter (1992), light (intensity, quality, and photoperiod) is highly variable and can change over a tremendous range, often very rapidly.Fish move within their environment, affecting the light that the fish receives.Although continuous illumination at 500 lx is favorable (Mapunda et al., 2021), it might not be convincing to consider optimum light intensity for early-stage snubnose pompano larvae because of the low survival (16.22%).Thus, the fish larvae may require a specific light intensity range on a particular day during its early stage.Reley et al. (2009) developed a refined feeding regime to provide stage-and-specific guidelines for feeding Florida pompano by applying initial light surface levels of 300 lx on 1 DPH.They increased into 2000 or 3000 lx on 2 to 20 DPH under hatchery conditions.Under increasing sunlight intensity at natural photoperiod, however, the growth of Trachinotus blochii larvae has been significantly reduced and caused a three-day delay in metamorphosis (Jayakumar et al., 2018).
Considering the behavior of the fish larvae in the natural environment and being receptive to the application of an artificial light system and extended day length (photoperiod), improving the rearing conditions can play an essential role in enhancing rearing conditions for early-stage snubnose pompano larvae.The influence of continuous illumination at increasing light intensities artificial system in the fish is still unknown.Thus, the current study investigates its effect on the feeding, early survival, and growth of 1 to 10 DPH snubnose pompano larvae.

Materials And Methods
The study was conducted at the Southeast Asian Fisheries Development Center Aquaculture Department (SEAFDEC/AQD), Tigbauan, Iloilo, Philippines.
Early-stage snubnose pompano Trachinotus blochii produced according to Alejos & Serrano Jr 3 method were subjected to five treatments with three replicates (Table 1) from 1 to 10 DPH.Following a Completely Randomize Design (CRD), treatments were assigned randomly in 15 tanks (200L capacity).Incandescent bulbs (Firefly, frosted standard, 100watts, 230v 60Hz, E27 medium base) were installed 30 cm above the water surface of experimental tanks for 300-500 lx and 300-1000 lx treatments and 80 cm for 300-2000 lx and 300-3000 lx treatments.Each tank was covered entirely with black sacks to remove the influence of background light on the experiment.Light intensity was controlled using a dimmer switch (Omni, model WDM-501-PK., 500 watts).For the control treatment, tanks were covered with transparent plastic cellophane and maintained under an indoor natural photoperiod (12hL: 12hD).Surface light intensity in various treatments was measured using a light meter (EXTECT measurements, EA30-EasyView™ Wide Range Light Meter).Natural light intensity in the control treatment was measured thrice daily (0900H, 1200H, and 15000H).
Fish larval culture and the sampling method for data collection were according to Alejos & Serrano Jr 2 .Using SPSS version 20 software, data were subjected to One-way ANOVA.When a significant difference between treatment means was confirmed, orthogonal contrast was applied, with a significance level of p<0.05.

Feeding
The influence of continuous illumination at increasing light intensities was apparent in feeding incidence and food intake of larvae during the day and night phases (Tables 2 and 3).Significant differences were observed at 1900H on 3 DPH, wherein larvae at 300-500 lx had the highest feeding incidence (Table 2).However, no significant differences in larval food intake were identified from 0400H to 2200H on 3 DPH.At 4 and 5 DPH, larvae at natural photoperiod had significantly higher feeding incidence and food intake during the day phase at 1000H than at light treatments but significantly lower during the night phase at 2200H and 0400H.At 0400H and 1600H on 4 DPH and 1600H on 5 DPH, no significant differences in food intake and feeding incidence of larvae were observed between treatments.
Comparison of day and night phases on feeding incidence and food intake of the fish larvae exposed to the different treatments are presented in Tables 4 and 5. Significant differences were observed on 5 DPH wherein larvae at natural photoperiod had higher feeding incidence during the day than larvae at light treatments.The feeding incidence of larvae at light treatments was significantly higher than that at natural photoperiod during the night phase from 4 to 5 DPH.In terms of food intake, no significant differences were observed on 3 DPH in the night phase and 5 DPH in the day phase, while significant differences were observed on 3 DPH in the day phase, 4 DPH both in the day and night phase, and on 5 DPH at night phase.
The result shows that larval first-feeding was observed at higher light treatments (300-1000 lx, 300-2000 lx, and 300-2000 lx) at 0400H on 3 DPH, while no feeding activity for the larvae at moderate light treatment (300-500 lx) and natural photoperiod.During light treatments, however, there is no clear indication of the larvae's food cycle.A comparison of feeding incidence and food intake (Tables 4 and 5) during the day and night phases showed that larvae were more active during the day phase on 3. Values were expressed as mean ± S.E.Values in the same column with different superscript letters differ significantly (p<0.05).
Values were expressed as mean ± SEM.
DPH but shifted to the night phase from 4 to 5 DPH.The feeding incidence of larvae at light treatments gradually increased from 0400H (3 DPH), then markedly decreased at 0400H for 300-500 lx, 300-2000 lx, and 300-3000 lx and at 1000H for 300-1000 lx (4 DPH).After that, larvae at 300-1000 lx, 300-2000 lx, and 300-3000 lx had an increasing feeding incidence during the day phase and markedly decreased during the day phase at 1000H from 4 to 5 DPH.Feeding incidence for the larvae at 300-500 lx showed inconsiderable changes over time, both day and night phases, after 3 DPH.
As shown in Table 5 and Figure 2, larvae had increasing daily food intake in all treatments.However, the negative effect of high light intensity was apparent after the onset of feeding at 0400H on 3 DPH.Larvae at 300-2000 lx and 300-3000 lx had considerably lower, and slight food intake changes from 0400H on 3 DPH to 1000H on 4 DPH.For the larvae at 300-500 lx and 300-1000 lx, food intake (Figure 2) gradually increased from 0400H and 0700H on 3 DPH and markedly decreased at 0400H and 1000H, respectively, on 4 DPH.After that, larvae at 300-1000 lx, 300-2000 lx, and 300-3000 lx had an increased food intake during the day phase and markedly decreased during the day phase at 1000H from 4 to 5 DPH.For the larvae at 300-500 lx, food intake showed slight changes over time, both day and night, after 3 DPH.In contrast, larvae under natural photoperiod typically feed during the day phase.Unexpectedly, around 3% feeding incidence was observed during the night phase at 0400H on 4 DPH.Feeding incidence (Figure 1) and food intake gradually increased during the morning and decreased during noon.The highest feeding usually occurred between 1000H and 1600H.Recorded natural light intensity inside control treatment (indoor) from day 1 to 10 DPH ranged from 9 to 372 lx.On 8 DPH, inconsistent data on the feeding of larvae were obtained, which shows a clear indication of the negative impact of daylight intensity fluctuation at natural photoperiod and high levels of light (300-1000 lx, 300-2000 lx, and 300-3000 lx).
The feeding response of the larvae generally indicates that regardless of how lighting methods are applied, average feeding success increases as larvae develop in all treatments.However, significantly lower success was observed in larvae at the natural photoperiod, which justified the findings of Alejos and Serrano Jr 3 .The larvae normally underwent diurnal rhythms, and the ever-changing daylight intensity (9-372 lx) affected their foraging activity.In a similar study, Villamezar et al. 12 found that European seabass Dicentrarchus labrax larvae exposed to constant light intensity increased their capture success following their developmental stage.The larvae identified and ingested prey easily due to visual acuity.In the study of Stuart & Drawbridge 13 , the advantage of continuous light was observed at or soon after the day of the first feeding of California yellow-tail Seriola lalandi and White seabass Atractoscion nobilis larvae.At 3 to 5 DPH, a significantly higher number of rotifers and or artemia were found in their guts.
The feeding response of the larvae also indicates that changing light intensity conditions from low to high levels during rearing altered the feeding behavior of early-stage snubnose pompano larvae because the results showed no clear indication of feeding pattern.Thus, larvae might feed actively during the night or day (Table 5).In the Alejos & Serrano Jr 2 study, larvae reared at 500 lx continuous illuminations displayed precise diurnal feeding despite 24 hours of light.It suggests that adaptation to different increasing light ranges had something to do with the feeding rhythms of early-stage snubnose pompano larvae.Yoseda et al. 14 reported that the three species of grouper (Plectropomus leopardus, Epinephelus akaara, and Epinephelus malabaricus) posse's precise circadian rhythm despite the 24-hour light conditions.

Growth and survival
The fish growth and survival exposed to the treatments are presented in Table 6.There were no significant differences in the total length of the larvae observed from 3 to 4 DPH.However, larvae at 300-1000 lx and 300-2000 lx had considerably smaller total lengths on 3 DPH.Significant differences in the total length of larvae start on 5 DPH.Larvae at light treatments were significantly larger at 0400H than the larvae at natural photoperiod.From 3 to 5 DPH, a gradual increase in larvae's total length was apparent at 300-500 lx, 300-2000 lx, and 300-3000 lx than at 300-1000 lx and natural photoperiod.After that, the negative effect of higher light intensity levels on the survival of larvae was apparent after 5 DPH, and then mass mortality occurred at 7 DPH.
Consequently, there was no consistent data on growth and survival during the late stage of the experiment.Only a single replicate remained from 300-1000 lx, 300-2000 lx, 300-3000 lx, and natural photoperiod (12hL: 12hD).Exposing the fish larvae to continuous illumination at increasing light intensities (Table 7) can achieve greater weight and total length at 300-2000 lx and 300-2000 lx, respectively.However, larvae exposed to 300-500 lx had consistent survival.In contrast, larvae at indoor natural photoperiod had the poorest growth and survival performance.
The applications of continuous illumination at different light intensities influenced the larval culture performance of early-stage snubnose pompano larvae 3 .Larval feeding, growth, and survival were favored when reared at 500 lx continuous illuminations from 1 to 10 DPH.In this study, the larval culture performance of the fish larvae showed different results when exposed to continuous illumination at increasing light intensities.Slower total length development and reduced foraging success were achieved from 3 to 5 DPH.However, more remarkable growth (F.L. and F.W.) and improved survival were obtained after 10 DPH.Food is the primary factor in fish development; however, some physical characteristic of like proper lighting, is essential factors that influence larval visual perception.Adjusting this parameter may increase efficiency and thus contribute positively to growth and survival rates 15 .Values were expressed as mean ± SEM (300-500 lx) *Control, 300-1000 lx, 300-2000 lx, and 300-3000 lx (n=1)

Conclusion
In conclusion, better and consistent feeding and survival of early-stage snubnose pompano Trachinotus blochii could be obtained at moderate continuous illumination at increasing light intensities (300-500 lx), but more remarkable fish growth at higher light treatments (300-1000 lx, 300-2000 lx, 300-3000 lx).However, changing light intensity conditions from low to high levels during rearing altered the feeding behavior of the fish larvae.Higher light intensities negatively affected the fish larvae' survival after 5 DPH.Under natural photoperiod, larvae normally underwent diurnal rhythms, and the ever-changing daylight intensity affected their foraging activity, leading to poorer growth and survival than those at light treatments.

Figure 1 .
Figure 1.Changes in the feeding incidence of early-stage snubnose pompano larvae under continuous illumination at increasing light intensities

Figure 2 .
Figure 2. Changes in the food intake of early-stage snubnose pompano under continuous illumination at increasing light intensities provided.
Continuous Illumination at Increasing Light Intensities and the Effects on the Growth and Survival Snubnose Pompano Trachinotus Blochii in the Early Stage

Table 1 .
Continuous illumination at increasing light intensities in between days.

Table 4 .
Comparison of the day-and night-phase feeding incidence of early-stage snubnose pompano under continuous illumination at increasing light intensities.

Table 5 .
Comparison of the day-and night-phase feeding incidence of early-stage snubnose pompano under continuous illumination at increasing light intensities.

Table 7 .
Growth and survival of early-stage snubnose pompano larvae under continuous illumination at increasing light intensities after 10 DPH