Introduction

In the Indian Sub-continent two main types of trout viz. brown trout Salmo trutta fario and rainbow trout Oncorhynchus mykiss were transplanted from Europe primarily to develop sport fishing or recreational angling (Jhingran and Sehgal, 1978; Singh and Lakra, 2011). Trout introduction in India dates back to late 19^th and early 20^th century under colonial rule by British, who made independent efforts in north-western and peninsular region of the country where suitable cold water for trout is available (Vass et al., 2010). In peninsular India, the very first attempt to introduce trout eggs and fry from New Zealand was made in 1863 by Sir Francis Day in Nilgiri and a hatchery was constructed in Avalanche in 1909-1910 (Jhingran and Sehgal, 1978; Gopalakrishnan et al., 1999; Sehgal, 1999a; Sehgal, 1999b). In the Munnar high range of Kerala, establishment of trout fishery started in 1909 with the introduction of brown trout Salmo trutta fario which could not succeed and therefore, after 1938 the focus shifted towards rainbow trout farming for aquaculture production in coldwater areas in India.

Today rainbow trout farming in India are existing in different parts of Himalayas such as the Kashmir, Himachal Pradesh, Sikkim, Uttarakhand and of late Arunachal Pradesh. On a small scale, it is also cultured in Ooty in Tamil Nadu and Munnar in Kerala in Deccan Plateau (Figure 1).

In northwestern regions of India, most suitable climatic condition and topography for trout farming exist in Jammu and Kashmir and Himachal Pradesh which are important states where rainbow trout farming has progressed on large scale. The trout fish farming project with the assistance of European Economic Community (EEC) in the year 1984 at Kokernag in Kashmir, tremendously helped developing trout farming in the state. Himachal Pradesh is the next leading states in rainbow trout farming and seed production in India with the assistance of Norwegian Government during 1989 - 91. In central Himalaya, Uttarakhand while in northeastern Himalaya, Sikkim and Arunachal Pradesh have now initiated producing trout. Although rainbow trout production is very low in these states but recently many farmers and entrepreneur have adopted trout farming and thus contributing to the total trout production. In the state of Arunachal Pradesh trout broodstock and seed production is being done in two main hatcheries situated at Shergaon of west Kameng and Nuranang in Tawang district. Shergaon has ova production capacity of 100,000. However, rainbow trout farming is yet to reach private farmers in the state. In central Himalayan region, Uttarakhand is one of the promising states where trout farming has good prospects.

Production status of rainbow trout in India

Trout farming has progressed steadily during last decade in India and the total trout production in the country elevated from 147 tonnes during 2004-05 to 842 tonnes during 2015 - 2016 which is over five-fold. Jammu & Kashmir, Himachal Pradesh and of late Sikkim are leading states where trout farming is undertaken in both private & public sectors. The ICAR - DCFR has been steadily working towards refinement of culture and breeding techniques of this high value fish for the benefit of hill fish farmers.

The production in India has increased remarkably from 755.27 (2014 - 15) to 842.23 tonnes (2015 - 16), with a growth rate of 11.51 percent (table-1). The trout production of J&k was 265 tonnes; Himachal 417 tonnes; Sikkim 120 tonnes while other states including Uttarakhand and Arunachal Pradesh was 40 tonnes during the current year 2015 - 16 (Figure 2).

Recently, Himachal Pradesh is one of the leading states in rainbow trout farming and seed production in India. The rainbow trout production in the state has increased from 351.27 tonnes (2014 - 15) to 417.23 tonnes (2015 - 16) leading to 18.78% growth. The state fisheries department own five trout farms and seed production unit in the state. The largest one is located in Patlikuhal in Kullu district. At present private sector is contributing major share (96%) of the total trout production in the state. Trout production in Jammu and Kashmir remained almost consistent mainly due to flood during this year, when many trout farms washed out. However, new raceways have been created to revamp the infrastructure in private sector in J & K. In Sikkim, 30 new raceways have been created in private sector and remained organized in the seed & fish production. In Uttarakhand, new raceways have been created in Uttarkashi, Chamoli, Pithoragarh and Champawat districts.

Arunachal Pradesh has just started seed production of trout but trout culture in private sector. A constant technical support is being provided by ICAR-DCFR, Bhimtal to all hill states for promotion of trout farming and seed production.

The trout production infrastructure has also been developed steadily in the country during the last 20 years and presently around 62 trout farms exist under Government sector while other 1 241 numbers of raceways are spread over seven states in the western, north - eastern and peninsular region of the country. A total of 32 trout hatcheries with an estimated eyed ova production capacity of 13 million are present in the country which are mainly managed by the various state governments. These hatcheries or seed production units cater the need of farmers, private entrepreneurs and also supply to different government agencies for building their stocks. Moreover, it is estimated that over 1 181 numbers of private trout units exist in the private sector mostly located in the Himachal Pradesh, Jammu and Kashmir and Sikkim states (Table 1).

A good number of fish farmers are still not well aware about the technique of trout farming and its scientific culture practice and hence partially adopting modern culture technology. The ICAR - Directorate of Coldwater Fisheries Research, Bhimtal has made concerted research and development efforts to popularize trout production in hill states and to refine location specific farming practices. Further, a basic database to understand the constraints in the expansion of trout culture as well as identification of potential areas for the introduction of trout farming was generated through field surveys. These findings indicate that there is ample scope for further enhancement of trout production in hill states through participatory approach and scientific management. Potential success in trout production requires better governance and significant improvement in the management practices through adequate R & D support. In order to achieve the goal of enhancing trout production, the ICAR - DCFR has been working hard to improving the existing technologies or developing new approaches for increased and sustained production.

Maturity and Breeding periods in different Himalayan States

Rainbow trout normally although attains sexual maturity at an age of 3 years however, feeding strategy, temperature, light conditions significantly influence it. We have observed that maturity and breeding of rainbow trout differs comparatively in different Himalayan states. In Sikkim, temperature remains comparatively on higher side with an optimal range of 14-18^°C for 8 months in a year as compared to J&K the prime trout state consequently rainbow trout performs breeding during second week of November. However, in Himachal Pradesh rainbow trout performs breeding earlier than J&K due to slightly higher thermal regime. In Uttarakhand, temperature remains 1-3.2^°C higher at ICAR - DCFR trout farm in Champawat than the other states it usually breeds during the first week of January (Table 2). The age range of females producing the highest quality eggs was observed as four years and the average number of eggs per kilogram of female body weight varies between 1 500 to 2 000 at different locations.

Major R & D Initiatives

In recent years, farmers have shown greater interest in commercial trout farming. Production enhancement of rainbow trout in the country needs both vertical and horizontal expansion. Requirement of technological advances in the form of improved feed having low FCR, farm design with greater efficiency, optimization of stocking density, broodstock maintenance and hatchery practices is necessary for the future development of trout farming in India (Pandey and Ali, 2015). Marketing of the final produce is another constraint in the spread of rainbow trout farming. Since farms are located in remote areas in the hills with poor transportation facilities, access to market is a real challenge. Trout is a high value low volume fish and highly perishable commodity, the produce needs to be transported in shortest possible time under refrigerated condition to fetch good price. In the absence of cold chain facilities and reliable market linkage, expansion of rainbow trout farming on a commercial scale will be difficult. Value addition of the final produce will be needed to increase sales and consumption of rainbow trout. Moreover, certain basic issues need to be scientifically addressed.

A. Culture environment

The DCFR undertook R&D activities to evaluate the comparative growth performance of the rainbow trout Oncorhynchus mykiss from different Himalayan states. At experimental farm, Champawat, Uttarakhand the recorded average growth was 200 g, 1 100 g and 2 100 g at first, second and third year of rearing respectively at the thermal regime of 4.5-20^°C (Joshi et al., 2005). In another field study in central Himalaya, average growth was recorded as 300 g (range 260 - 400 g) at thermal regime of 5.0 - 22^°C (Vass et al., 2010). The reported / generated information suggested that higher temperature in mid altitudes of Himalayas can help better yield of rainbow trout, provided farm management practices are optimized (Pandey and Ali, 2015). Generally, it takes 12 - 14 months to attain marketable size (250 – 260 g) in J & K, Himachal Pradesh and Garhwal region of Uttarakhand. However, comparatively better growth of 500 – 600 g was observed in 12 months at state Govt. farm and private farms in West Sikkim. This was due to favourable thermal range of water (14-18 ^°C for 8 months in a year) and availability of sufficient water volume. In Nepal, marketable size of 200 - 300 g reaches at 14 - 16 months of culture period with the stocking density of 50 fish/m² (Swar, 2007; Rai et al., 2008). Whereas the fish takes approximately 8 months to reach a market size of 300 – 350 g in trout farms of Idaho, U.S.A after being stocked in  raceways when 4 inch long fingerling stocked (Gempesaw et al., 1995). In general, the production level of rainbow trout in Indian conditions ranges 300 - 500 kg per raceway of the size of 15 m x 5 m x 1 m (45 m²) in 12 months. However, productivity of 1 tonnes / raceway or more has been achieved at government and private trout farms of J & K, Kullu valley of Himachal Pradesh and also West Sikkim. With regard to stocking density, a flow rate of 4 LPS can support up to 20 kg/m³, though higher volume and higher quality may allow stocking densities as high as 35 kg/m³. A minimum rate of 500 m³ per day of water flow is necessary for 1 tonne of trout produced (Stevenson, 1987). With growing intensification of trout culture, flow-through aquaculture systems like raceways and tanks discharge effluents with enhanced concentrations of nutrients and solids are receiving attention (Green et al., 2002; Pulatsu et al., 2004; Bartoli, et al., 2007) and biotic communities (Camargo et al., 2011). However following physico-chemical conditions are always ideal for trout farming (Table 3).

B. Breeding strategies for maintaining imported Genetic stocks of rainbow trout in India

The Himalayan aquaculture is mainly depending on introduced fish species i.e., the rainbow trout and the carp. Therefore, it is important to manage the introduced stocks on scientific genetic management basis so as to maintain variability in the stock and minimize inbreeding. We have developed breeding strategies for such species. Based on the historical records of import and time to time translocation of rainbow trout to different parts of the country (Singh and Lakra, 2011), it has been worked out based on microsatellite markers that three different stocks are present in the country viz. Himachal Pradesh stock, Jammu and Kashmir stock and Munnar hill stock (Southern India) (Barat et al., 2015). Other states share the rainbow trout stocks from these three stocks which have been brought for either building their new stocks or replacing old stocks. Therefore, hatchery managers and stakeholders are advocated to practice brood raising and breeding practices on scientific basis and in consultation with the ICAR-DCFR from time to time.

C. Nutrition and Feed formulation

It has been recommended that a diet of no less than 35% crude proteins be administered at a rate of 2 - 3% of bodyweight per day for grow - out stock of rainbow trout. The nutritional value of the feed depends not only on the quantity but also on the quality of the protein, i.e., its amino acid conformation. Amid acids are the elementary units of proteins. Several amino acids are essential to fish growth and development and, therefore, must be present in the feeds. Proximate composition of carcass of fingerlings of rainbow trout reflected that the requirement of Arginine (6.427%) is comparatively higher than the other essential amino acids. Therefore, better utilization of the protein in the diet of trout should be obtained by adding ingredient having more Arginine (Fontagné - Dicharry et al., 2017).

However, use of protein for energy is expensive, thus lipids are primarily included in formulated diets to maximize their protein sparing. Lipids are a highly digestible source of concentrated energy. Dietary lipid level as low as 10% has been suggested for rainbow trout on the basis of previous studies. Generally, weight gain and feed efficiency depressed when diet contains 15% or more lipids (Kamalam et al., 2017). Rainbow trout has an exclusive requirement of n-3 or w3 PUFA in their diet. High protein level in the diet is always resulted an increase in unwanted ammonia excretion. It was observed that diet with 45% and 40 % protein level resulted as 0.12 mg/l and 0.08 mg/l ammonia excretion in the drain water, respectively. But, lowest level of 0.05 mg/l ammonia was recorded with 35% protein level in the diet.

A major researchable issue for trout feeding is the high cost of manufactured pelleted feed due to the use of largely imported fish meal. The increasingly scarce supply of fish meal and its high market price had made it necessary to seek a cost effective replacement of fish meal to supply dietary protein in trout feed. For addressing the issue, two cost - effective practical starter feeds were formulated for first feeding rainbow trout fry, based on single or multiple protein sources. The experimental diets were made up of commercial ingredients and were conventionally prepared by steam cooking, pelleting and drying. To evaluate the performance of these two diets as compared to a widely used commercial diet, a five week feeding trial was conducted and found more efficient and significant over the commercially used starter feed (Figure 3).

D. Health Management

Pathogenic bacterial profiling of rainbow trout farms of Himachal Pradesh, Uttarakhand and Sikkim was conducted. Major pathogenic bacteria characterized from the samples were Citrobacter freundii, Pantoea agglomerans, Aeromonas hydrophila, Aeromonas veronii, Hafnia alvei, Pseudomonas fluorescens, Plantibacter sp, Morganella sp, Staphylococcus sp, Plegiomonas sp, Carnobacterium maltaromaticum & Corynebacterium sp. Surveillance of rainbow trout farms at different locations observed bacterial diseases like tail rot, gill rot, fin rot and exophthalmia. Skin hemorrhagic ulcers on the caudal regions of rainbow trout were also observed, characterized by deep ulcers and hemorrhagic frayed fins. The causative agent was identified as Aeromonas hydrophila (designated RTMCX1). Amplification and sequencing of the 16S rRNA gene (1 304 base pair) revealed that the sequence was 99% similar to A. hydrophila sub sp. hydrophila. This strain exhibited strong ß-hemolytic activity against sheep blood and rainbow trout erythrocytes, and was capable of growing in rainbow trout serum and 0.5 - 10% NaCl at 4.0 - 35°C. Mortality was 100% in experimentally-infected fish, with a median lethal dose (LD50) of 1.9 × 10⁴ colony forming units/g body weight. Aeromonas hydrophila, RTMCX1 was sensitive to a majority of 27 tested antibiotics, indicating the possibility of controlling this bacterium by antimicrobial compounds. Four strains of Lactococcus garvieae (GenBank accession no: KM 604701, KM 604702, KM 604703 and KM 604704) were isolated and identified from diseased rainbow trout in trout farms of Uttarakhand and Himachal Pradesh. Samples were showing typical symptoms of lactococcosis; unilateral exophthalmia, inflammation and swollen vent, petechial haemorrhages in viscera, focal haemorrhages and swelling in liver (Shahi et al., 2013; Mallik et al., 2016). Further, disease surveillance of trout farms was conducted in Himachal Pradesh and Jammu & Kashmir under National Surveillance Programme on Aquatic Animal Diseases (NSPAAD). So far a total of 25 fish farms from three states namely, Jammu and Kashmir, Himachal Pradesh as well as Uttarakhand were surveyed. Screening of coldwater fish viruses i.e., infectious pancreatic necrosis virus (IPNV) and viral haemorrhagic septicemia virus (VHSV) carried out in 206 collected unpooled samples were found negative suggesting the absence of the said viruses in our trout farms.

Pathogenic fungi that are commonly observed in trout farms are Saprolegnia parasitica and Saprolegnia diclina. They have characteristics of cotton like appearance, elongated zoosporangia and pear shaped primary sporangium. Temperature has been observed to have a significant effect on the appearance of fungal infection which becomes epizootics when temperatures are below the optimum range. However, during incubation of trout eggs it was observed that higher temperatures increased the chances of infection. Rayamajhi and Dhital (2008) suggested that polluted water, especially during monsoon season, and unhygienic feed are the most likely pathways for disease to enter Nepalese rainbow trout.

E. Processing, value addition and Marketing

Rainbow trout is one of the most well-known fish in the world, and has a reputation as being a high quality, coveted product that fetches a high price. But, trout farms in India are remotely located in difficult terrains and have poor accessibility to the markets. At times they are not well connected by road or rail. Under the circumstances, farmers are either forced to consume the produce by themselves or sell at cheaper prices in local market. Rural domestic consumption cannot become the target of the rainbow trout industry; it must look out to areas where the local produce has good market and demand (Swar, 2007). Considering marketing of the product, a “branding” technique, such as labelling the fish “Himalayan rainbow trout” has been thought to be adopted. Being a perishable item transportation of the fresh fish is very difficult. The long duration from time-of-harvest to arrival-at-market necessitates proper dressing, preserving and packaging techniques. Ice, cold storage and fish dryers are required to maintain the high quality of the trout meat. The introduction of value addition techniques to the produce is under process. In order to make the endeavour, the smoked trout and other value added products have been attempted with the technical support of ICAR - CIFT, Cochi. Our endeavour would not only preserve the produce and products but also would increase the net profit.

Conclusion

Rainbow trout farming has great potential in India hence skill up gradation/training to the trout growers for adopting scientific basis of farming for sustainable commercial farming is imperative. A comprehensive guideline and policy for trout farming and its promotion need be developed for sustainable production in cold-water regions. Strengthening of marketing channel, development of cold chain and facilities for processing and product development will be helpful in management and expansion of trout farming in India.

Future Strategies to invigorate trout farming

l  Expansion of trout farming in potential inaccessed areas.

l  Development of trout resource GIS maps for Himalayan region for sustainable utilization and management.

l  Development of cost-effective larval and grow out feed for trout.

l  Disease surveillance and fish health management.

l  Genetic management of existed introduced trout stock and exploring fast growing strains for further import.

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