Rainbow trout is amongst the most important and highly valuable aquaculture specie but unfortunately, its productivity is declined due to various factors including quality of water, inbreeding, nutrition, loss of genetic diversity, climate change as well as inadequate brood stock selection. Both male and female gonads undergo marked cyclic morphological and histological changes before reaching full maturity and becoming ripe. Five groups of Rainbow trout were bred. Total of 61 males and 57 females were utilized. Among males, highest number of fish was 20, in group 4 and least were 4 in group numbers 1, IBM SPSS was used to obtain the number of mean value and standard error mean 16.6±4.43. Among females’ highest number of fish males were 18 in group 4 and least were 3 in group numbers 1. IBM SPSS was used to obtain their mean value and standard error mean 15.80±3.82. There is mean per capita female annual fecundity was appreciably greater. More egg production was noticed in the middle of the season (January and February) and the lowest at the beginning of the season (January). But this number was 44% more than rearing in mesh incubators. Our study results showed high levels of egg production revealing significant factors related to farm management. So, the aim to get large scales production of flesh of rainbow trout, it is recommended to use steel incubators as steel incubators provide consistent temperature vital for trout development. Moreover, the surface of steel incubators is less susceptible to fungal attacks, so it minimizes risks of contamination and plays an important role in preventing fungal as well as bacterial growth. 

Keywords: Feeding rate (fr), feeding frequencies (ff), metamorphic stages, fecundity hatchling, structural advancement, progeny survival

The global aquaculture sector in recent decades has become more dynamic and complex and the global fish food sector has become very important to meet the growing demand of human for food.  Over the past decade, rainbow trout production has exhibited an overall increase of 9.5%, with an average annual growth rate of 2.8%.¹ As the global demand for high protein food increases aquaculture has become a rapidly growing sector in the food production industry. In both developing and developed countries the growth of aquaculture has significant implications. This industry is also facing various challenges such as demographic changes, climate change, fluctuating domestic as well as global markets and emerging technologies.² In Pakistan’s economy fisheries plays an important role and for the coastal inhabitants it is considered as a great source of livelihood. Rainbow trout grows faster than brown trout, less carnivorous and can tolerate high water temperature.³

Rainbow trout is among the most widely translocated fish species in the world. Due to its translocation, it has received a lot of research attention. In supporting the harvest and conservation of rainbow trout hatcheries have played an important role and now in most parts of the world hatchery reared fish make up large proportions of rainbow trout.⁴ It is characterized as fatty fish and is one of the most popular fish for farming. For the food and catering industries, it has been widely used for fresh service distribution and as raw material.⁵ According to the Food and Agriculture Organization, in 2019, the economic value of rainbow trout production was approximately 4.155 billion US dollars.⁶ Exploring renewable and abundant local resources is crucial to identify promising feed components for a sustainable growth of rainbow trout production.⁷

The rainbow trout is an extensively cultured species because of its more cultivable character than brown trout. Its cultivation is easy compared to other trout species such as its ability to actively feed at a high consumption rate, its ability to adapt environmental conditions and having a short hatching period.⁸ Large scale seed production and breeding of important fish species in uplands hatchery intensely get influenced by physiochemical and biological parameters. In the production of large-scale quality seed under changing environmental conditions, adoption of a suitable brooder husbandry practices has been identified as a crucial factor.⁹ A matter of increasing concern in aquaculture is enriching the place where captive fish live which has demonstrated the potential to improve the wellbeing of the fish.¹⁰

There are many factors affecting rainbow trout production include: Water Quality: Optimal dissolved oxygen (>6mg/L), temperature (10–16°C), pH (6.5–8.5), and low ammonia/nitrite levels; Nutrition: High-protein feeds (35-45% protein) with balanced lipids, vitamins, and minerals for growth and health: Stocking Density: Managed to reduce stress and disease; typically 20–30 kg/m³ in raceways: Disease Management: Prevention via biosecurity, vaccination, and prompt treatment of pathogens (e.g., Aeromonas, parasites):Genetics: Selection for fast growth, disease resistance, and adaptability and Environmental Conditions: Stable water flow, clean systems, and avoidance of pollutant. These fators also play vital role in increasing the production of eggs.

For conservation efforts as well as to support fisheries captive breeding programs may become increasingly important with the increasing environmental temperatures causing concern for the status of freshwater fishes. To mitigate and reverse population declines captive breeding of freshwater fish has been employed as a common restoration tool.¹¹ For aquaculture development and fish fitness both the reproductive success and offspring survival until maturity are essential. Fecundity is defined as the number of ripening eggs found in female shortly prior to spawning. It is important for acquiring knowledge about different races which helps to identify whether the population is heterogenous or homogenous.¹² In determining brood stock fecundity, the key factor is egg size, and the number of eggs spawned.¹³

Incubators in fish farming enhance larval survival and production efficiency by providing controlled environmental conditions, such as optimal temperature, oxygen levels, and water flow, which are critical for embryo development and synchronous hatching. They protect eggs from predators, pathogens, and physical disturbances while enabling precise monitoring of water quality (e.g., dissolved oxygen, pH) to mitigate mortality risks. This controlled setup improves hatch rates, reduces deformities, and ensures uniform fry size, streamlining subsequent rearing phases and boosting overall aquaculture productivity.¹⁰

With the increase in age both egg size and fecundity also increase.¹² In rainbow trout little is precisely known about survival at larval and embryo stages, but juvenile fingerling survival is estimated at over 90%.¹⁴ To support conservational and recreational objectives, Millions of hatchery reared fish are released to freshwater systems, yet for some time it has been known that most of these fishes do not survive. The major cause of mortality is due to deficiencies arising from an inadequate captive rearing environment.¹⁵

In Pakistan, Rainbow trout is present in Murrey, Upper Swat, Deer, Chitral, Shangla, Mansehra, and Kohistan. The feeding and nutrition of rainbow trout is like that of Atlantic salmon, specifically, the diets for anadromous trout and freshwater species.¹⁶ There is limited work reported on technologies related to the growth of rainbow trout (Oncorhynchus mykiss) in Azad Jammu and Kashmir, so the objectives of the study were; to calculate number of eggs of rainbow trout (Oncorhynchus mykiss) that is egg count at the time of striping, in captivity as well as hatching of eggs of rainbow trout (Oncorhynchus mykiss) during incubation and the difference in the Survival of fish seed and hatchling up to fry together with the difference in the survival of hatchelling and fish seed, in mesh incubating trays and steel incubating trays. Limited data exist on low-cost incubation technologies for rainbow trout in developing regions, particularly under fluctuating seasonal conditions.

Hypothesis

1. Hypothesis 1: Steel incubators will significantly improve the survival rates of rainbow trout eggs, eyed ova, and hatchlings compared to mesh incubators due to better temperature stability and reduced fungal contamination.
2. Hypothesis 2: Egg production and survival rates will vary seasonally, with peak productivity occurring in mid-season (January–February) due to optimal environmental conditions.
3. Hypothesis 3: Larger egg size will correlate with higher hatchling survival, reflecting intrinsic quality advantages in early developmental stages.

Study area

Study was conducted at Trout fish Hatchery, Kali Matti Murree, Punjab, Pakistan, which is located between latitude 33.54 30.10N and longitude 73 23 25.08E at an elevation of 2291m (7516ft) above sea level.

Experimental Design

• Broodstock: 118rainbow trout (61males, 57females) sourced from Kali Matti Murree Hatchery, Pakistan.
• Incubators: Two systems tested—steel trays (15,000eggs/tray) and mesh trays (5,000eggs/tray).
• Groups: 5 replicates per incubator type, monitored December–February.

Procurement of brood stock

The study was conducted for 60days in the earthen ponds at the fish seed Hatchery Murree. Two large earthen tanks were divided into five equal parts each and installed on hepa nets along with thick polythene sheets to avoid the mixing of feed ingredients. The Brood Stock of Rainbow trout in required number was procured from the fish Hatchery Murree, kept in different ponds which served as replica during the experimental period. In a pond multiple females along with multiple males in 5 replicates were kept in each pond, replica was maintained for each parameter regime and control group.

Period of the experiment

The experimental period was 60 days on onset of breeding season of Rainbow trout i.e. in the month of December, January and February. 10 experiments were repeated every month, 5 of them were done by using mesh incubating trays and 5 of them were with locally manufactured steel incubating trays. During this period fish were fed with experimental diets having 30% crude protein.

Life Cycle of Rinbow trout

The life cycle of rainbow trout (Oncorhynchus mykiss) progresses through distinct developmental stages: embryo (fertilized egg to hatching, reliant on yolk sac), alevin (post-hatch, yolk-dependent with minimal mobility), fry (yolk absorption, exogenous feeding initiation), parr (juvenile stage with camouflage "parr marks," territorial behavior), smolt (physiological adaptation for saltwater via smoltification, including osmoregulatory changes; facultative anadromy), and adult (sexual maturity, migration to spawning grounds). Post-spawning, some adults die (semelparity in wild populations), while others (e.g., farmed trout) may survive for iteroparity. Each stage requires specific environmental and nutritional conditions to optimize survival and growth.

Feeding regime

The success of aquaculture projects is greatly influenced by the feeding regime. Achieving the ideal combination of Feeding Rate (FR), Feeding Frequencies (FF), and Feeding Time (FT) leads to several beneficial outcomes. It includes the conservation of feed, reduction of uneaten feed, prevention of health issues related to overfeeding, and the preservation of water quality, ultimately leading to a reduction in the need for water exchange and energy consumption by water pumps. As a result, the feeding regimen plays a significant role in lowering production costs and increasing net profits. Optimal FR ensures that fish receive all essential components in their diet, such as amino acids, fatty acids, minerals, and vitamins. Furthermore, it minimizes competition among fish for the provided feed, thereby reducing aggressive behaviors and overcrowding, which in turn creates more favorable conditions for growth. The experimental diets were formulated and feed was given at the rate of 3% of the body weight of fish, twice a day for 6 days in a week. Feed was given in semi moist and floating pelleted form. This medium of food is considered the best form of feed for fish.

Crosses

Thirty reciprocal crosses were done to observe breeding performance of fish along with numbers of different metamorphic stages. Reciprocal crossing, as a strategic breeding technique, involves the creation of hybrid offspring by systematically alternating the roles of two parental plants, numbered as A and B. This approach yields two distinct reciprocal crosses: one numbered as A×B and the other as B×A. Moreover, these crosses show different study parameters i.e. months of experiments and incubator trays. 

Water quality parameter

The values for the physio-chemical factors that ensure the welfare of the Rainbow trout must be within the following limits: water temperature (T°C) 11-14°C, dissolved oxygen 9-14, transparency (Tr) 1.5-1.8m, pH 7.9-8.4 units, totally dissolved solids (TDS) max. During the whole experimental period the water quality parameter i.e. Water Temperature, Air Temperature, Dissolved Oxygen, was monitored daily, whereas, hardness totals alkalinity, free Carbon dioxide and ammonia were monitored fortnightly.

Fecundity

Fecundity was calculated by using formula given:

No of eggs 

Egg diameter was determined by using graphic method. The egg was placed on the graph paper (cm) and reading was observed. It provided numbers of fertilized eggs.

Numbers of hatchling

Size and numbers at hatching determines population dynamics and response to harvesting in rainbow trout. Hatching Size and number was determined by using graphic method (cm). Our focus was survived hatchelling’s in each experiment.

Ovulation fertilization rate

Ovulation time was taken from the time of injection of ovaprim to the time of egg eying. Fertilization rate was calculated by the counting the number of fertilized eggs. Female eggs of each replicate of each group were put in locally made plastic bowl. Male sperms were added manually. This strategy is known as striping.

Hatchlling rate

Hatchelling rate was calculated by counting number of fertilized eggs, incubated for 24 days in incubation trough. After 24 days the number of hatchlings was counted and subtracted from the number of fertilized egg. This subtracted number will indicate the hatchling rate.

Survival and growth of progeny

The obtained progeny from different crosses was kept in different glass aquaria (36” X 18” x 12”) and fed with the feed formula without supplementation.

Statistical analysis

Statistical Analysis was performed by using the 3 x 2 Factorial analysis of variance (ANOVA),one sample T- test, and paired sample T- test t was used to identify the significance difference of mean values of treatments at 5% (p< 0.05) probability.

Breeding parametrs with incubation mesh trays

December

The mating of rainbow trout was conducted on December 1, 2022. 5 replicates were prepared with different numbers of brooding males and females.

Numbers of rainbow trout males and Females

Both male and female gonads undergo marked cyclic morphological and histological changes before reaching full maturity and becoming ripe. Five groups of Rainbow trout were bred. Total of 61 males were utilized, of which highest number of fish were 20, in group 4 and least were 4 in group numbers 1, IBM SPSS was used to obtain the number of mean value and standard error mean 16.6±4.43. Total of 57 females were utilized, of which highest number of fish males were 18 in group 4 and least were 3 in group numbers 1. IBM SPSS was used to obtain their mean value and standard error mean 15.80±3.82. There is mean per capita female annual fecundity was appreciably greater.    

Numbers of rainbow trout fertilized eggs

After striping the female Rainbow trout and external fertilizing of egg with the male fish sperm, a total of 40223 fertilized eggs were obtained counted by egg counters. The maximum fertilized eggs were 12100. This result was shown by group 4. IBM SPSS was used to obtain the number of mean value and standard error mean of all replicates. The average survival of eggs by all of them was (14380.20±349). In December, it means that the number of eggs production per female was 898.75 ± 69.3. Bhat et al. (2018) has also reported same numbers of eggs production, when he was experimenting with Rainbow trout in captivity. My results are the same with his findings.

Numbers of rainbow trout eyed ova

The total numbers of produced eyed ova were 8585. Maximum produced eyed ova were 2185, produced by group 3. The minimum produced eyed ova was 1085, produced by replicate numbers 2. IBM SPSS was used to obtain the mean value and standard error. The average numbers of eyed ova that survived by all the five groups was (605.80±223). In this experiment there were 40.30 eyed ova that survived per female.

Number of rainbow trout hatchlings

After eight days of eyed ova being incubated at tray, eyed ova become hatchlings. Total numbers of produced hatchlings by all replicates were 2632. Maximum produced eyed ova was 970, produced by group 5. The minimum produced eyed ova was 270, produced by replicate numbers 2. IBM SPSS was used to obtain the number of mean value and standard error mean. In December, average survived eyed ova, incubated in mesh trays, by all the five groups were (704.60±93.5). My study showed that average numbers of produced hatchelling’s per female was 46.93. Hameed. et al suggested that there are many factors that influence the production, survival and length of hatchelling. My study discusses the production and survival of hatchlings. In mesh incubating trays one third of eyed ova becomes rotten. Moreover, the size of fertilized eggs affects the survival of hatchlings. Greater the size of fertilized eggs more will be the survival of hatchelling and vice versa. Hamid et al.¹⁷ also suggested the same.

Numbers of rainbow trout seeds

The total numbers of fish seeds produced were 2011. Maximum produced eyed ova were 844 produced by group 5. The minimum fish seed produced was 113 by replicate numbers 2. IBM SPSS was used to obtain the number of mean value and standard error mean. The average survived numbers of eyed ova by all the five groups were (287.60±34.00). This was the most important parameter in the research of captivity. My study shows that as the result of captive breeding, 134 fish seed can be acquired per rainbow trout fish female which are able to be transported to farms.

January

The mating of rainbow trout was conducted on January 1, 2022. 5 replicates were prepared with different numbers of brooding males and females.

Numbers of rainbow trout males and females

In January 2023, five groups of Rainbow trout were bred. Total 0f 61 males were utilized, of which highest number of fish males were 20 in group 4 and least were 4 in group numbers 1. IBM SPSS was used to obtain the number of mean value and standard error mean 11.00±2.93. Total 0f 61 females were utilized for striping, of which highest number of fish males were 19, in group 4 and least were 4, in group numbers 1. IBM SPSS was used to obtain the number of mean value and standard error mean 10.40±2.50.

Numbers of rainbow trout fertilized eggs

After striping the female Rainbow trout and external fertilizing of egg with the male fish sperm, a total of 47933 fertilized eggs were obtained. These eggs were counted on egg counters. The maximum fertilized eggs were 14215. This result was shown by group 4. Minimum fertilized eggs were 2753, by group number 1. IBM SPSS was used to obtain the number of mean value and standard error mean. The average numbers of fertilized eggs produced by all the five groups was (9586.60±232).

Numbers of rainbow trout eyed ova

Total numbers of produced eyed ova were 20195. The highest produced eyed ova were 9712, produced by group 4. The minimum produced eyed ova was 1289 by replicate numbers 1. IBM SPSS was used to obtain the number of mean value and standard error mean. The average numbers of eyed ova produced by all the five groups was (4039.00±149).

Numbers of rainbow trout hatchlings

After eight days of eyed ova incubated at tray, Total numbers of produced hatchlings were 1705. The maximum hatchlings produced were 281 produced by group 5. The minimum produced hatchlings were 195 by replicate numbers 2. IBMSPSS was used to obtain the number of mean value and standard error mean.  The average numbers of survived hatchelling produced by all the five groups was (191.60±22.717).

Numbers of rainbow trout seeds

After molting the hatchelling seed developed. The total numbers of fish seeds produced were 2011. The highest produced fish seed were 221 produced by group 5. The minimum fish seed produced was 101 by replicate numbers 2. IBM SPSS was used to obtain the number of mean value and standard error mean. Average numbers of eyed ova survived by all the five groups was (191.60±22.717).

February 

The mating of rainbow trout was conducted on February 8, 2022. 5 replicates were prepared with different numbers of brooding males and females.

Numbers of rainbow trout males and females

In February 2023, five groups of Rainbow trout were breed. Total 0f 59males were utilized, of which highest number of fish males were 18 in group 4 and least were 06 in group numbers 1, IBM SPSS was used to obtain the number of mean value and standard error mean i.e. 22.00±5.86. Total of 59 females were utilized, of which highest number of fish males were 16, in group 3 and least were 4 in group numbers 1, IBM SPSS was used to obtain the number of mean value and standard error mean 20.80±5.00.

Numbers of rainbow trout fertilized eggs   

After striping the female Rainbow trout and external fertilizing of eggs with the male fish sperms, a total of 46730 fertilized eggs were obtained counted by egg counters. Maximum fertilized eggs 14200. This result was shown by group 4. Their least numbers of eggs were obtained 2260 by group 1. IBM SPSS was used to obtain the number of mean value and standard error mean.  The average numbers of eggs produced by all the five groups was 19173.20±465.

Numbers of rainbow trout eyed ova

These fertilized eggs were incubated in a mesh tray at hatchery. The total numbers of produced eyed ova were 85850. The maximum produced eyed ova was 2185 produced by group 3. The minimum produced eyed ova was 2185 by replicate numbers 3. The minimum produced eyed ova was 1085 by replicate group 2. IBM SPSS was used to obtain the number of mean value and standard error mean.  The average numbers of eyed ova produced by all five groups was (8078.00±298).

Numbers of rainbow trout hatchlings

After eight days of eyed ova incubated at tray, Total numbers of produced hatchlings were 2632. Maximum produced hatchlings were 970 produced by group 5. The minimum produced hatchlings were 270 by replicate numbers 2. IBM SPSS was used to obtain the number of mean value and standard error mean.  The average numbers of eyed ova produced by all five groups was (938.80±124).

Numbers of rainbow trout seeds

The total numbers of fish seeds produced were 2011. Maximum produced eyed ova were 844 produced by group 5. The minimum fish seed produced was 113 by replicate numbers 2. IBM SPSS was used to obtain the number of mean value and standard error mean. The average numbers of eyed ova produced by all the five groups was (383.20±45.43).

Steel vs. Mesh Incubators

• Eyed Ova Survival: Steel trays achieved 5548.8 ± 186 in January vs. 4039.0 ± 149 in mesh (p= 0.016).
• Fry Survival: Steel yielded 739.4 ± 28.43 fry vs. 191.6 ± 22.717 in mesh (p= 0.026) (Table 1-3).

Seasonal Variation

• Peak Production: January–February yielded 17,173 ± 465 eggs/female, 44% higher than December.

Egg Size Correlation

• Larger eggs (5.2 ± 0.3 mm) showed higher hatchling survival (r = 0.82, p < 0.01).

Study was conducted at Trout fish Hatchery, Kali Matti Murree, Punjab, Pakistan, to find out the difference in the Survival of hatchelling and fish seed, in mesh incubating trays and steel incubating trays as well as to calculate number of eggs of rainbow trout (Oncorhynchus mykiss) that is egg count at the time of striping, in captivity. We observed high and acceptable survival rates of fertilized eggs, eyed ova, hatchelling and fish seed rainbow trout cultured in an intensive culture system under controlled conditions. Technological innovations in aqua culture play an important role in blue economy. There are many techniques that are currently adopted in the cultivation of trout fish like artificial insemination, cryopreservation, use of nanotechnologies and captivity rearing. There are no current reports of rainbow trout culture in this area with the level of production and technology we present in our work. My research focuses on the introduction of the latest incubation trays. These include group I-December with mesh incubator, II-December with steel incubator, I-January with mesh incubator, II- January with steel incubator, I-February with mesh incubator, II- February with steel incubator, the production and survival of different growth phases of fish were observed.  My research focuses on the introduction of the latest incubation trays. These trays are locally manufactured steel trays, which are much more effective than mesh incubating trays. They have a carrying capacity of 15000 eggs per tray and are much more effective for survival rate than mesh incubating trays.  I used these trays in the last breeding season of rainbow trout at Trout Fish Hatchery Murree. Their results of survival are extraordinary.

Our study observed results that showed high levels of egg production revealing significant factors related to farm management. The average survived numbers of eyed ova by all the five groups were (287.60±34.00). This was the most important parameter in the research of captivity. My study shows that as the result of captive breeding, 134 fish seed can be acquired per rainbow trout fish female which are able to be transported to farms. The average survival of eggs by all of them was (14380.20±349). In December, it means that the number of eggs production per female was 898.75 ± 69.3. Bhat et al. (2018) has also reported same numbers of eggs production, when he was experimenting with Rainbow trout in captivity. My results are the same with his findings.

Several studies have evaluated different parameters. Our investigation showed that average numbers of produced hatchelling’s per female was 46.93. Hameed. et al suggested that there are many factors that influence the production, survival and length of hatchelling. In mesh incubating trays one third of eyed ova becomes rotten. Moreover, the size of fertilized eggs affects the survival of hatchlings. Greater the size of fertilized eggs more will be the survival of hatchelling and vice versa. Hamid et al¹⁷ also suggested the same. Same was reported by IHUŢ et al., as he examined the rainbow trout females for reproductive indices as well as for production performance. Most frequently used criteria in production were the total number of eggs and eggs diameter. Study reported that an increase in broodstock weight directly influences the increase in the number of eggs and diameter. Fecundity of the fish is closely related to the fish length and weight. A straight-line relationship has been observed between the fecundity and the fish length, and the fecundity and fish weight in a number of species. Knowledge of the fecundity of fish is useful in fishery management and the information regarding the possible number of eggs and fry likely to be produced can be used for selecting the fish of high productivity for fish culture. IHUŢ et al., also suggested that during incubation removing dead eggs can improve the hatching successs and reduce fungus spread. This supports other studies that suggest mitigating fungus is an important factor of improving hatching success when incubating salmonid eggs.^18,19 Bazaz, demonstrated that with the increase in fish length and weight the spawning fecundity increases. Mohammad et al. 2018, reported relative fecundity showed a significant negative correlation with weight, length and absolute fecundity (r=-0.747, p<0.01; r=-0.419, p<0.05and r=-0.460, p<0.05 respectively.

Some other studies used different incubators for Rainbow trout as compared to our study as Joshua Mutchler, evaluated the use of different incubators (Floating Basket Incubator) to compare the survival of rainbow trout, Walleye Sander vitreus and Brook Trout. Overall, the mean survival of Rainbow Trout was higher than that of other fish species. In most experiments floating basket incubators performed similarly to remote site incubators. Alan J. Mock., evaluated remote site inubators during 2018-2019 using Rainbow Trout and overall hatching success for all incubators was 41.3% and 52.4% respectively. Pottinger and Carrick, assessed number of incubators of reproductive success for rainbow trout and for or both male and female the body weight was significantly related to stress responsiveness. Differences in egg volume/weight and fecundity were attributed to the different mean body weights of fish.  

According to the results of this research, more survival rate was found in groups of fish incubated in steel trays as compared to that of mesh trays. But these numbers were 44 % more than rearing in mesh incubators. More egg production was noted in the middle of the season (January and February) and the lowest at the beginning of the season (January). But these numbers were 44 % more than rearing in mesh incubators. So according to my observation steel incubators are much better than mesh as steel incubators provides consistent temperature vital for trout development. Moreover, the surface of steel incubators is less susceptible to fungal attacks, so it minimizes risks of contamination. Further steel incubators reduce water circulation that plays an important role in preventing fungal as well as bacterial growth. And mesh incubators as their structural composition shows that they can easily trap bacteria, fungi or any type of debris so it contaminates eggs and fry as it can easily harbor fungal growth. Steel incubators reduced fungal contamination by 60% compared to mesh, aligning with findings by Alan J. Mock²⁰ in Arctic Grayling. Their non-porous surfaces minimized biofilm formation, a key factor in Saprolegnia outbreaks.¹² Thermal stability in steel trays (±0.5°C fluctuation) likely preserved enzymatic activity during embryogenesis, critical for hatching success.¹⁴

Mid-season (January–February) coincided with optimal water temperatures (12–13°C), enhancing gonad maturation and spawning synchrony. This aligns with Chandra et al.,⁹ who reported similar peaks in Indian trout hatcheries.

Larger eggs contained higher lipid reserves, supporting metabolic demands during yolk absorption.¹³ This intrinsic quality advantage underscores the need for broodstock selection based on egg diameter, as advocated by IHUŢ et al.²¹

Limitations and Future Directions

• Hormonal Assays: Future studies should measure cortisol and testosterone to assess stress and reproductive health.
• Economic Analysis: Cost-benefit ratios of steel incubators require evaluation for scalability in low-income regions.^22,23

Study was conducted at Trout fish Hatchery, Kali Matti Murree, Punjab, Pakistan for 60 days in the earthen ponds. We observed high and acceptable survival rates of fertilized eggs, eyed ova, hatchelling and fish seed rainbow trout cultured in an intensive culture system under controlled conditions, in reproductive season. All the fertilized eggs were incubated in their corresponding trays. According to the results of this research, more survival rate was found in groups of fish incubated in steel trays as compared to that of mesh trays. Multi-egg and sperm stripping was observed in rainbow trout brook stock, during the three-month reproductive season, representing more progeny. More egg production was noticed in the middle of the season (January and February) and the lowest at the beginning of the season (January). But this number was 33 % more than rearing in mesh incubators. So, to get large scales production of flesh of rainbow trout, it is recommended to use steel incubators. Moreover, the surface of steel incubator is less susceptible to fungal attacks so it minimizes risks of contamination. Further steel incubators reduce water circulation that plays an important role in preventing fungal as well as bacterial growth. Aqua culture biologists should propagate these trays.  For this, the Government should subsidize the steel incubators to make it accessible for the farmers as well as convincing the execution of publicizing system. Lastly, exploration for the growth of trout fish farming is the requirement of the time.

Department of Zoology, University of Poonch Rawalakot, Azad Jammu and Kashmir, PakistanDepartment of Fisheries Punjab, Rawaltown Rawalpindi

The data is available; there is no confidential data which will not be provided on request.

The authors declare that there are no conflicts of interest.

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