Carp and Mono-Sex Nile Tilapia Polyculture in a Cemented Tank

TABLE OF CONTENTS

Title

ACKNOWLEDGMENT

TABLE OF CONTENTS

LIST OF TABLES

LIST OF FIGURES

LIST OF APPENDICES

ABBREVIATIONS

ABSTRACT

1 INTRODUCTION
1.1 General introduction
1.2 Objectives
1.2.1 General objective
1.2.2 Specific objectives
1.3 Limitations of the study

2 LITERATURE REVIEW
2.1 Global status of aquaculture
2.2 Status of aquaculture in Nepal
2.3 Carp polyculture
2.4 Principle of carp polyculture
2.5 Pros and cons of carp polyculture
2.5.1 Pros of polyculture
2.5.2 Cons of polyculture
2.6 Carp-Nile tilapia polyculture
2.7 Culture species
2.7.1 Labeo rohita (Hamilton, 1822)
2.7.2 Hypophthalmichthys molitrix (Valenciennes, 1844)
2.7.3 Hypophthalmichthys nobilis (Richardson, 1845)
2.7.4 Ctenopharyngodon idella (Valenciennes, 1844)
2.7.5 Cyprinus carpio (Linnaeus, 1758)
2.7.6 Oreochromis niloticus (Linnaeus, 1758)
2.8 Stocking
2.10 Water quality requirements for carps and Nile tilapia
2.11 Feed and feeding
2.11.1 Natural food
2.11.2 Supplementary food
2.11.3 Liming
2.11.4 Fertilization
2.11.5 Yield and FCR
2.11.6 Economics of carp and Nile tilapia polyculture

3 MATERIALS AND METHODS
3.1 LEE site
3.2 Tank preparation
3.2.1 Draining and drying
3.2.2 Liming
3.2.3 Tank filing
3.2.4 Fertilization
3.2.5 Stocking of fingerlings
3.3 Tank management
3.3.1 Feed and feeding
3.3.2 Fertilization
3.3.3 Water quality monitoring
3.4 Fish sampling
3.5 Fish harvesting
3.6 Marketing of fish
3.7 Analytical methods
3.7.1 Fish growth parameters
3.7.2 Gross margin analysis
3.7.3 Statistical analysis

4 RESULTS
4.1 Water quality
4.1.1 Daily diurnal monitoring
4.1.2 Weekly monitoring
4.2 Fish growth and production
4.2.1 Silver carp
4.2.2 Bighead carp
4.2.3 Grass carp
4.2.4 Rohu
4.2.5 Common carp
4.2.6 Nile tilapia
4.2.7 Growth, survival, and yield of all fishes
4.3 Gross margin and Fish marketing

5 DISCUSSION
5.1 Water quality
5.2 Growth and yield of fish
5.3 Gross margin and fish marketing

6 CONCLUSION

LITERATURE CITED

APPENDICES

BIOGRAPHICAL SKETCH

ACKNOWLEDGMENT

The work presented in this thesis would not have been possible without my close association with many people. I take this opportunity to extend my sincere gratitude and appreciation to all those who made this thesis possible.

First and foremost, there are no proper words to convey my deep, sincere gratitude and respect for my advisor Professor Sunila Rai, PhD, who has been a tremendous mentor for me. I have been fortunate to have a supervisor who cared so much about my work, and who responded to my questions and queries so promptly. Thank you for your invaluable contributions to making this work a reality, and as well as constructive criticisms, untiring efforts, and continuous entertainment of discussions and guidance throughout the work.

Special thanks must go to our LEE coordinator Assistant Professor Rahul Ranjan for his continuous support, guidance, cooperation, encouragement, and for facilitating all the requirements, going out of his way. His constant guidance, cooperation, motivation, and support have always kept me going ahead.

I sincerely appreciate the encouragement and support from Professor Dilip Kumar Jha, PhD, and Adjunct Faculty Jaydev Bista. I would like to thank them for their valuable suggestions and support throughout my study period.

I would like to acknowledge the Dean, FAVF, AFU, for providing an opportunity of LEE and for the financial support and Aquaculture Farm, for all the necessary items required for this study. I must thank the staff of the Fisheries Program, Tulsi Adhikari, Pancha Gurung, Tanka Dawadi, Arpan Malla, Surya Gurung, and Binod Lama for their kind support and their timely help whenever required throughout my work.

I wish to express my sincere appreciation to my colleagues for their challenging and productive criticism. I thank you all for listening to me, providing me advice, and supporting me throughout this entire LEE. I feel a deep sense of gratitude for the most significant indirect contribution to this work, who are my grandparents, mother, father, and guardians who formed part of my vision and taught me good things that matter in life. As always, it is impossible to mention everybody who had an impact on this work. Finally, my thanks go to all the people who have supported me to complete the work directly or indirectly.

LIST OF TABLES

1 Species combination in carp polyculture system in Nepal

2 Water quality requirements for Nile tilapia

3 Water quality requirements in carp

4 Trophic and spatial niche of carp and Nile tilapia

5 Dietary nutrient requirements of carp and Nile tilapia

6 Liming requirement in pond culture at preparation and during production

7 Liming dose for different soil pH value

8 Fertilizer requirement in pond culture

9 Stocking density of carps and Nile tilapia in the tank

10 Water quality parameters and their analysis methods

11 Mean and range of daily water temperature (˚C) (mean±SD)

12 Mean and range of transparency (cm) (mean±SD)

13 Mean and range of water depth (cm) (mean±SD)

14 Mean and range of daily DO (mg/L) (mean±SD) recorded at different time

15 Mean and range of daily pH (mean±SD) recorded at different time

16 Combine water quality parameters recorded of tank water during the culture period

17 Mean and range of diel monitoring water quality parameters weekly basis

18 Average water quality parameters monitored during culture periods

19 Growth and production of carps and Nile tilapia

20 Combined growth and production of carps and Nile tilapia

21 Contribution of carps and Nile tilapia in combined fish production

22 Gross margin analysis

LIST OF FIGURES

Daily temperature (˚C) of tank water during culture periods

Daily transparency (cm) of tank water during the culture period

Daily water depth (cm) of tank water during the culture period

Daily DO (mg/L) of tank water during the culture period

Daily pH of tank water during the culture period

Diel fluctuation of temperature (˚C) of tank water

Diel fluctuation of DO (mg/L) of tank water

Diel fluctuation of pH of tank water

Average weight (g/fish) of silver carp during the culture period

Average weight (g/fish) of bighead carp during the culture period

Average weight (g/fish) of grass carp during the culture period

Average weight (g/fish) of rohu during the culture period

Average weight (g/fish) of common carp during the culture period

Average weight (g/fish) of Nile tilapia during the culture period

Average weight of fish species during sampling

Contribution of carps and Nile tilapia in combined production

LIST OF APPENDICES

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ABBREVIATIONS

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ABSTRACT

Name: Saurav Lamichhane AFU Registration No.: 2-1-343-2015

Semester and Year of Admission: First, 2016 Degree: B. Sc. Fisheries

Advisor: Prof. Sunila Rai, PhD Department: Fisheries Program

Carp polyculture is the most common, popular, and successful aquaculture system in Nepal. Including mono-sex Nile tilapia in carp polyculture could enhance fish productivity. This present LEE work was conducted at the Fish hatchery complex of Fisheries Program, Agriculture and Forestry University, Rampur, Chitwan, in a cemented tank of area 25 m² for 26 days (03rd October to 29th October 2020) to study the carp and mono-sex Nile tilapia in a polyculture system. Hypophthalmichthys molitrix (1.5±0.7 g/fish), Hypophthalmichthys nobilis (4.2±1.3 g/fish), Ctenopharyngodon idella (7.6±3.0 g/fish), Labeo rohita (12.1±6.7 g/fish), Cyprinus carpio (25.2±5.2 g/fish), Oreochromis niloticus (43.1±16.6 g/fish) were stocked in the ratio of 4: 2: 4: 3: 4: 3 with 2 fish/m2 density. The tank was limed using agricultural limestone at the rate of 125 kg/ha. The pond was fertilized using urea and DAP at the rate of 4.7 g/m²/week and 3.5 g/m²/week respectively. Fishes except Grass carp were fed twice daily with the pellet made from mustard oil cake and rice bran mixed at a 1:1 ratio at the rate of 5% BW. Grass carp were fed with duckweed at a rate of 50% BW twice a day from 7:30 am to 8 am and 1:30 pm to 2 pm. Water quality parameters i.e., water temperature, transparency, water depth, dissolved oxygen, and pH and were monitored daily while total alkalinity was monitored weekly. Sampling of fish was done fortnightly to check fish growth and adjust feed quantity. All the water quality parameters were within the optimal range of fish production except for DO which was very high during the afternoon. The extrapolated GFY and NFY were 14.5 t/ha/yr and 9.6 t/ha/yr, respectively. The overall survival of fish was 87% and AFCR was 1.4. The total variable cost and the production cost was NRs. 220/kg. Fishes were transferred to the Aquaculture farm, assuming the selling rate NRs. 300/kg. This makes the total gross return was of NRs. 875, making a total net profit of NRs. 327. The B: C ratio was 1.59. From this LEE work, it was concluded that carp and mono-sex Nile tilapia polyculture is a reliable and profitable venture to carry out. Saurav Lamichhane Student

1 INTRODUCTION

1.1 General introduction

Polyculture is an art and science of growing two or more compatible fish species in a pond to maximize production by taking advantage of different spatial distribution and feeding habits (Zimmermann, Nair, & New, 2009). Polyculture is also known as multi-trophic aquaculture (Bunting, 2008). This idea of multispecies fish culture was derived originally from the philosophy of harmony, i.e., harmonization of the relations among man, matter, and nature (Tang, 2011). Polyculture concepts rely on the complete utilization of various spatial niches and trophic of a pond to acquire a maximum production per unit area. Thus, the compatible species of complementary feeding habits are stocked to utilize all the ecological niches of the ecosystem effectively (Singh, Maqsood, Samoon, Verma, Singh, & Saxena, 2020).

Carp polyculture is the most common, popular, and successful aquaculture system in South Asia, including Nepal. It has become a means to counter the different problems of rural farmers like malnutrition, low income, and food security (Woynarovich, Moth-Poulsen, & Péteri, 2010). Carp polyculture includes three Indigenous major carps (IMC) along with three Chinese carps and common carp. These include Indigenous major carps: rohu (Labeo rohita), mrigal (Cirrhinus mrigala) and bhakur (Labeo catla), and Chinese carps: bighead carp (Hypophthalmichthys nobilis) silver carp (Hypophthalmichthys molitrix), and grass carp (Ctenopharyngodon idella), common carp (Cyprinus carpio). Although carps feed at low in the food chain and accept both natural food and artificial feed, the indigenous carps have a slow growth rate (Uddin, Shahjahan, & Haque, 2012).

Carp polyculture is the major aquaculture system contributing to more than 90% of total aquaculture production in Nepal. In 2018/19, total fish production, aquaculture, and productivity were 91,832 t, 70,832 t, and 4.92 t/ha, respectively (CFPCC, 2019), which is insufficient to fulfill the growing demand for fish in Nepal. Therefore, it is essential to increase production and productivity. Including mono-sex Nile tilapia in carp polyculture could enhance fish productivity (Bhujel, 2014) because tilapia grows faster. Moreover, Nile tilapia is an omnivore (Wang & Lu, 2015) and is compatible with carps.

Polyculture of carps and mono-sex Nile tilapia under the Learning Entrepreneurial Experience (LEE) program was practiced in a tank to learn the semi-intensive aquaculture system and fish marketing.

1.2 Objectives

1.2.1 General objective

- To learn to produce carps and mono-sex Nile tilapia in polyculture in the cemented tank and market fish.

1.2.2 Specific objectives

- To monitor the water quality parameters in a carp-Nile tilapia polyculture tank.
- To determine the growth and production of different carps and Nile tilapia.
- To calculate the gross margin of carp and Nile tilapia polyculture.
- To learn marketing of fish.

1.3 Limitations of the study

This study had access to the prominent polyculture techniques of five different carps with mono-sex Nile tilapia in the cemented tank aligned with its production. Time, resources, and marketing constraints had limited LEE work. Due to the limited culture period, proper growth and marketing size of fish could not be attained which affected the marketing of fish. Proper recording of water quality could not be done due to the malfunctioning of the machine and the unavailability of distilled water and reagents. Marketing was not done properly due to small fish size and less mobility of people and fear among the people due to COVID-19.

2 LITERATURE REVIEW

2.1 Global status of aquaculture

Global fish production will continue to expand over the next decade even though capture fisheries had peaked its level and aquaculture no longer enjoy the high annual growth rates of the 1980s and 1990s (11.3 and 10.0 %). The State of World Fisheries and Aquaculture (SOFIA) reports that total aquaculture production will grow to 201 million metric tons (Mt) by 2030 (FAO, 2020a).

In 2018, global fish production reached 178.5 Mt out of which fisheries and aquaculture contributed 96.4 and 82.1 Mt respectively. Inland and marine waters contributed 51.3 Mt and 30.8 Mt in aquaculture, respectively. The total aquatic algae production was 32.4 Mt. The annual growth rate on an average is 5.3 % during 2001−2018. Global per capita consumption of fish was 20.5 kg in 2018. Major finfish species in aquaculture production are grass carp (5.7 Mt), silver carp (4.7 Mt), Nile tilapia (4.5 Mt), common carp (4.1 Mt), catla (3.0 Mt), rohu (2.0 Mt) (FAO, 2020a).

2.2 Status of aquaculture in Nepal

Nepal is a fascinating landlocked country situated in the southern slopes of the Himalayas (Shrestha, 2008). Fisheries have been a strong tradition and long practiced in Nepal. Fish is considered auspicious and signifies the symbol of power, prosperity, and productiveness. It is one of the staple dishes in many communities in Nepal and is an essential source of food as it is healthy, rich in protein, and low in calories and cholesterol levels.

Aquaculture is a new activity and started in the early 1950s. Aquaculture is mainly done in Terai-plain, including carp production in the pond and cages in lakes and reservoirs and raceways in the hilly region (Rai, Clausen, & Smith, 2008).

In 2018/19, total fish production was 91,832 t out of which capture and aquaculture contributed 21,000 t and 70,832 t respectively. The pond aquaculture contributed to 62,725 t which is almost 90% of total aquaculture production. The pond productivity was 4.92 t/ha. Bara district has the highest fish production of 7,886 t while Rupandehi district has the highest productivity of 5.8 t/ha. The total fish consumption was 3.11 kg per individual. Fish contributes 20.75% of the total meat consumption. The total import of edible fish was 9,334 t which is at a decreasing rate. Fish contributes 4.18% and 1.13% in the AGDP and GDP, respectively. (CFPCC, 2019).

2.3 Carp polyculture

Polp polyculture is the most viable and common aquaculture system in Nepal. There are different types of carp polyculture, which is practiced to enhance productivity. The major and established system of Nepal is a semi-intensive carp polyculture. The main species under culture are rohu, naini or mrigal, bhakur, silver carp, bighead carp, grass carp, and common carp (Hussain & Yadav, 2016). 2. yculture is a production system where two or more species of fish with different ecological habitat and food preferences are cultured together in such densities that there will be almost no competition for space and food (Shrestha & Pandit, 2012). Polyculture is characterized by low investment, quick return, high profit, and rapid growth in yield, and meet the needs for raising the living standard of the people (Lin, 1982). The two main aspects that significantly influences the level of intensities of operation of polyculture systems are stocking densities and species combination (Jena, Ayyappan, Aravindakshan, Dash, Singh, & Muduli, 2002). The monoculture production is much more feed dependent than polyculture unless low stocking densities are practiced (Woynarovich et al ., 2010). Besides, the choice of species in a polyculture system should be based on the following criteria: availability of fish seeds, availability, and cost of other inputs such as feeds, fertilizers, and productivity of the system (Guerrero, Guerrero, & Ala, 1988).

Car4 Principle of carp polyculture The motivating principle is that a combination of different species can maximize fish production. Different species combinations in a polyculture system effectively utilize available natural food produced in a pond and contribute to improving the pond environment. Polyculture management is based on the relationship between organisms at different levels of the food chain (Singh et al ., 2020). Therefore, the selection of species plays a vital role in the polyculture system because all of the species should benefit from the available food without competing with one another (Yin, Zhu, Zhou, Li, Wang, & Liao, 2017). In this system, food niches are enriched by using fertilization or supplemental feeding, but only with a proper combination and densities will utilize it efficiently. A suitable combination of species will maximize the synergistic and minimizes antagonistic fish-fish and fish-environment relationships.

Synergistic interaction is based on two processes: improved environmental conditions and an increase in food resources. The mechanisms through which different fish species contribute to the improvement of environmental conditions depend on the specific levels of the food chain at which they feed (Milstein, 1992). An example of increased availability of food resources is illustrated by the Chinese proverb `feed one grass carp well, and you feed three other fish (Opuszynski, 1986). At the macrophytic level, grass carp ingest many plant materials and decrease excess plant growth, which prevents nocturnal oxygen deletion. Moreover, its feces are the source for detritivorous fish and have a fertilization effect on phytoplankton, which is grazed by silver carp at the planktonic level. Besides, feces of silver carp which have partially digest phytoplankton are being eaten by common carp, which otherwise would not have been utilized. At the benthos level, common carp stir the mud, which would recirculate nutrients helps the development of phytoplankton, thus food for silver carp. As grazing on algae, it will control bloom and avoid the risk of O2 depletion, thus improving the heterotrophic food chain, improving bottom-feeding fish. At the heterotrophic level, detritivorous fish helps in the improvement of water quality. Tilapia feed on sediment, preventing an increase in organic load and increasing ammonia level (Milstein, 1992).

In unbalanced conditions, the system is affected in different ways according to the level of the food chain where the imbalance occurs. At the phytoplankton level, excessive silver carp may lead to ichytyo-eutrophication caused by overgrazing of large algae promoting small algae. Overstocking of bighead will lead to the consumption of copepods, chironomid larvae, which are also basic food of common carp. Bottom fish might affect others by interfering with other food and reproduction by destroying nest during food search. Overstocking of grass will eliminate macrophytes and a concurrent increase in feces resulting in phytoplankton bloom.

The principal tool for maximum production and polyculture management is the knowledge of fish-fish and fish-environment quantitative relationships. This helps in selecting appropriate combinations of species, stocking density, and other decisions according to the specific conditions. Polyculture is the appropriate technique when the goal is the production of low-cost fish or when fish feeds are not available (Milstein, 1992).

Principal requirements of different species in combination (Shrestha & Pandit, 2012)

- They should have complementary feeding habits.
- They should occupy different ecological niches.
- They should attain marketable sizes at the same time.
- They should all be non-predatory and tolerate each other.

2.5 Pros and cons of carp polyculture

2.5.1 Pros of polyculture

- Better utilization of the space and feeding niche.
- Full utilization of natural and formulated feeds.
- Low water quality and disease problems.
- Product diversity for household consumption and marketing in the same period.
- Risk diversification and more economic return than monoculture.

2.5.2 Cons of polyculture

- Skilled technical knowledge, expertise, and experience are required.
- Difficult to procure and synchronize fingerlings of the right size at the right time.
- Difficult to maintain the food for all species.
- Difficult in harvesting and low production.

2.6 Carp-Nile tilapia polyculture

Incorporating mono-sex Nile tilapia in the existing systems of carp polyculture will enhance the carp polyculture as when stocked at appropriate densities, tilapia grow well without affecting the performance of other species. The primary purpose of incorporating is to utilize natural foods as Nile tilapia feeds on many sources of food, thus increasing fish production (Bhujel, 2014). Since it consumes plankton, it will improve water quality in ponds and effluents at harvest. Such improvements in water quality and faster consistent growth will help to gain larger economic and production of fish with no further inputs to enhance the sustainability of aquaculture systems environmentally and economically.

Monosex solves unwanted reproduction and early sexual maturation problems. In comparison to the mixed population, monosex has a higher specific growth rate, daily weight gain, protein efficiency ratio, and protein content (Chakraborty & Banerjee, 2010). In populations, males grow approximately 50% faster and are uniform in size than females (Bhujel, 2014). The addition of Nile tilapia (3000/ha) and sahar (1000/ha) into the existing carps production system could increase yields by 30% and profit margin by 18% (Shrestha, Bhandari, Diana, Jaiswal, Mishra, & Pandit, 2018). Shrestha et al . (2018) and Pandit, Shrestha, Mishra, Wagle, and Diana (2018) have concluded that the addition of Nile tilapia to carp polyculture has increased the yield and production, so incorporating mono-sex Nile tilapia will be a profitable venture.

2.7 Culture species

2.7.1 Labeo rohita (Hamilton, 1822)

Rohu is found in rivers in the terai region of Nepal, north and central India, Pakistan, Bangladesh, and Burma (FAO, 2006). It is the most important and preferred species among IMC due to its higher growth rate, market demands, consumer preference, and taste (Nair & Salin, 2007). The body is moderately elongated, cylindrical with blue to brownish along the back, and silvery on the sides and belly. A distinct red mark appears on the scale during the breeding season, and the fins become greyish or black. Small pointed head, reddish eyes with a small pair of maxillary barbells are present. A sub-terminal mouth with thick-fringed and inner fold lips and three rows of pharyngeal teeth. Moderate size cycloid scales with 40-44 lateral line scales are present (Shrestha, 2008). The first-year growth is slow and attains around 900 g but can attain a meter length and 30 kg in weight during its course of a lifetime (Shrestha & Pandit, 2012).

2.7.2 Hypophthalmichthys molitrix (Valenciennes, 1844)

Silver carp is a native to Eastern Asia from Amur to Xi Jiang, and Hanoi, Vietnam (Ancevski, 2011). It is introduced for aquaculture and control of algal blooms but also for the enhancement of fisheries and water quality on occasion (Kolar, Chapman, Courtenay, Housel, James, & Jennings , 2005). It was introduced to Nepal in 1967 and 1968 from India and Japan, respectively (Shrestha & Pandit, 2012).

The body is laterally compressed, deep, and flat with olive green in color on the dorsal side and silver on the ventral side (Ancevski, 2011). Head is broad, with an upturned mouth and barbells are absent. The scales are small silvery, cycloid, and lateral line scale count typically range from 85 to 108. The ventral keel extends from isthmus to anus, i.e., complete from anterior vent to anterior breast portion, near gill membranes junction. Fins are dark without a real spine. The pectoral fins posterior margin does not extend beyond the pelvic fin base, or only less than 10% overlapping occurs (Shrestha & Pandit, 2012). Long, thin, fused sponge-like gill rakers, which are unique and highly specialized filtering, are present in two separate rows gill arch, creating a V-shaped cavity. It is extremely thin, sponge-like interlaced, and connected (Kolar et al ., 2005). The growth is about 1-2 kg in the first year and can attain up to 40-50 kg in its lifetime (Shrestha & Pandit, 2012). The highest growth rate in size and weight in the second and third years of life, respectively (Jhingran & Pullin, 1985).

2.7.3 Hypophthalmichthys nobilis (Richardson, 1845)

Bighead carp is native to large rivers of eastern Asia. It is a semi-migratory fish and recognized because of its versatility in aquaculture operations. (FAO, 2004a). It was introduced to Nepal in 1969 and 1972 from America and Hungary, respectively (Shrestha & Pandit, 2012).

The body is laterally compressed, deep-bodied, and flat with dark gray above and cream-colored below with dark gray to black irregular blotches on the back and sides. Turbid water may dissolve the blotched or mottled pattern. Head and mouth are extensive. The length of the head is more significant than body height with an upturned mouth and barbells absent. Eyes are situated low in the head, facing ventral and forward. Small, silvery, and brownish, cycloid scales are present, and lateral line scale count is from 96 to 110 Pharyngeal teeth are four in each arch with a single row and shape like a spoon with the grinding surface shallowly concave. Incomplete abdominal keel where it extends from anterior vent to base of pelvic fin. When the posterior part of the pectoral fin of a bighead is pressed, it extended well beyond the pelvic fin base, overlapping 16 – 42% of the length of pelvic carp. Pharyngeal teeth have fine striations. Long, thin unfused gill rakers are present. (Kolar et al ., 2005). The growth is about 1-2 kg in the first year and can attain up to 40-50 kg in its lifetime (Shrestha & Pandit, 2012).

2.7.4 Ctenopharyngodon idella (Valenciennes, 1844)

Grass carp is an herbivorous fish, originally from Vietnam, Amur River on China border (Cudmore & Mandrak, 2004; FAO, 2004b). It is an essential species used for weed control in water bodies (FAO, 2004b). It was introduced to Nepal in 1967 and 1968 from India and Japan, respectively (Shrestha & Pandit, 2012). The body is elongated and cylindrical, with the rounded abdomen, compressed at the rear, and the length of the caudal peduncle is twice the length of width. The body is greenish-yellow laterally, with dark brown dorsally and greyish white in the abdomen. Head is broad with the sub-terminal arch-shaped mouth and barbells absent. Two rows of pharyngeal teeth are present. Large cycloid scales with 39-46 scales on lateral lines. Short and spare gill rakers and the gill membrane is connected to the isthmus (Towers, 2010). Fast-growing fish with a growth of 1-2 kg in the first year and can attain up to 50 kg and 1.5 m in length in its lifetime (Shrestha & Pandit, 2012).

2.7.5 Cyprinus carpio (Linnaeus, 1758)

Common carp is native to rivers and lakes of Asia and Europe dwelling upon deep slow-flowing warm waters and can thrive in large turbid rivers. It is active at dusk and dawn. Hardy, tolerant of a wide variety of conditions and breeds along shores (FAO, 2004c). It was introduced to Nepal in 1956 and 1960 from India and Israel, respectively. Two varieties are mostly culture, i.e., German carp (Cyprinus carpio var. communis) and Israeli carp (Cyprinus carpio var. specularis) . German carp have golden scales covered wholly and uniformly, and whereas Israeli carp have few large shiny scales covered irregularly (Shrestha & Pandit, 2012).

It is also known as an ‘ecological engineer’ and nuisance fish because it causes dramatic ecological disruption to both the aquatic community and the ecosystem (Rahman, 2015). The body is deep, robust, heavy, with slightly compressed laterally. The mouth is underslug with a flashy protrusible lip, and a small head is a relatively small and complete lateral line. Long and serrated trailing edge on the first ray of the anal fin and dorsal fin. Two pair’s small barbells are present in the upper jaw (Shrestha, 2008). The maxillary barbells are shorter than the mandibular barbells. The growth of German is 1-2 kg in the first year, and that of mirror carp is 2-3 kg. It can attain up to 18 kg and 50 cm in length in its lifetime (Shrestha & Pandit, 2012).

2.7.6 Oreochromis niloticus (Linnaeus, 1758)

Nile tilapia is a species of Cichliformes order. It is tropical species native to Africa and the Middle East, distributed widely throughout the world. It is one of the most important food fishes in the world. It was introduced to Nepal from Thailand in 1985 (Shrestha & Pandit, 2012).

The body is laterally compressed to oval and deep, depending on the environment. Body-color depends on environmental, physiological, and dietary factors. Male brooders have a red flush in different parts like head, lower body, dorsal and caudal fins. Lateral line interrupted with 30-34 cycloid scales. Terminal mouth with teeth in 3 to 7 series and varying number. Truncate caudal fin with distinctive and regular 7 – 12 vertical stripes are present, which is a diagnostic feature (FAO, 2020b). Sexual maturity is attained around 5-6 months of age and at 20 g weight too. It is a prolific breeder and spawns spontaneously; that is why mono-sex tilapia is preferred. In a pond, a soft bottom nest is excavated using the mouth to lay eggs over there. Nile tilapia reaches around 50 g in 2-3 months. After that, it gains weight faster, whereas the growth rate remains constant per unit BW. The growth starts to slow down after reaching around 600-800g, but they still grow but at the asymptotic phase, i.e., decreasing rate (Bhujel, 2014).

2.8 Stocking

The stocking rate depends on the biological productivity, supplementary feeding, and water surface area of a pond. So, to maximize the capacity of the pond, four to seven species are stocked at the same time, but sometimes, due to interspecific competition, stocking time can be altered. In contrast, the species ratio depends on pond nutrients, fish seed accessibility, consumer, and market demand. Fingerling has a high chance of survival and better production than a smaller size despite being a little expensive (Rahman, Varga, & Chowdhury, 1992).

The desirable stocking rate is one fish/m2 and the desirable socking ratio is as below:

Table 1. Species combination in carp polyculture system in Nepal

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2.10 Water quality requirements for carps and Nile tilapia

The determining factor for fish production is water quality. Water quality requirements for carps and Nile tilapia are given in Tables 2 and 3, respectively. Nile Tilapia can tolerate a broader range of environmental conditions like temperature, pH, dissolved oxygen, and ammonia levels than most of the carps can (Mjoun, Rosentrater, & Brown, 2010).

Table 2. Water quality requirements for carp

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Table 3. Water quality requirements in Nile tilapia

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2.11 Feed and feeding

In a fish culture, feeding is the most decisive technology element as it directly determines the profitability of the production (Woynarovich et al ., 2010). Fish feed on two types of food: natural and supplementary.

2.11.1 Natural food

It includes the food that is produced in the pond itself like phytoplankton, zooplankton, macrophytes, detritus, etc. (Carballo, Eer, Schie, & Hilbrands , 2008). In general, 100 kg of phytoplankton can produce around 10 kg of zooplankton which in turn produces 1 kg of fish meat (Woynarovich et al ., 2010).

Table 4. Tropical and spatial niche of carp and Nile tilapia

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2.11.2 Supplementary food

It includes the feed that is supplied from outside to maintain the nutrients in the pond as the pond does not produce this feed. Feeds like vegetables (leaves, grasses), oil cakes (mustard, soybean), grain (rice, wheat barn), animal origin (fishmeal, poultry eggs), and additives (vitamins, mineral) are supplements feed and help to reduce the food conversion ratio (FCR) (Agropedia, 2012). Proper feeding of appropriate composition at the right time in a suitable amount so that the fish will accept it optimally. Once the fish reached a daily ration of around 3% BW, they are usually fed once or twice a day generally before mid-morning or late afternoon before dusk. The feeding rate and quantity are necessary to be adjusted, and it requires the number of fish and their total weight to adjust the rate so that they are not over or underfed (Stickney, 2005).

The feed conversion ratio (FCR) should be calculated each month, as well as at the end of the production season. The Thumb rule is that the FCR will be less during the first half of the production season, while it will be more in the second half. FCR of the same feedstuffs to younger fish will be lower than of elder fish because younger consume more natural protein-rich food, consequently, requires supplementary feed to gain 1 kg (Woynarovich et al ., 2010).

Generally, rice bran and mustard oil cake (MOC) are mixed at a 1:1 ratio to make supplementary feed for carps. Shrestha, Bhandari, Diana, Jaiswal, Mishra, and Pandit et al . (2018) and Pandit, Shrestha, Mishra, Wagle, and Diana (2018) feed carp+ tilapia with the local feed (rice barn + MOC) of 20% CP and 24% CP, respectively, at the rate of 2% BW, once each morning from 0900 to 1000 hours. Jha, Rai, Shrestha, Diana, Mandal, and Egna (2018) fed the carps with dough (rice barn + MOC) daily at 5% BW for 60 days, then 2% BW for 150 days every morning at 0900–1000 h, whereas Mandal, Rai, Shrestha, Jha, and Pandit (2018) fed the carps with 24% CP pellet at 3% body weight. Both of them feed grass carp with locally available grass at 50% BW. Rai, Gharti, Shrestha, Ranjan, and Diana (2018) feed carp with rice bran and mustard oil cake at 1.5% BW/d while grass carp were fed with grass and banana leaves at 50% BW/d.

Table 5. Dietary nutrient requirements of carp and Nile tilapia

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2.11.3 Liming

Areas with soft waters and acidic soils need liming but not in soils with a high concentration of carbonates (Egna & Boyd, 1997). Liming raises the alkalinity of the water and increases the availability of carbon dioxide for photosynthesis. So acidic and low alkalinity problems can be solved by lime.

The application of liming materials is not a type of fertilization (Boyd & Tucker, 1998). When agricultural limestone was applied to unfertilized ponds with low alkalinity, the production did not increase even at the highest application rate, 4480 kg/ha compared to un-limed ones. Therefore, liming is a technique for increasing the response to fertilization, not a substitute (Egna & Boyd, 1997).

Generally, two kinds of lime are used which are the powdered limestone, or agricultural lime which acts slowly, and the quicklime, which acts quickly and aggressively. Therefore, quicklime is better at disinfecting or at the treatment of water (Woynarovich et al., 2010).

Table 6. Liming requirement in pond culture at preparation and during production

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Table 7. Liming dose for different soil pH value

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2.11.4 Fertilization

Fertilizer increases the primary productivity by increasing the plant nutrients, which will lead to a higher abundance of natural food and an increase in the productivity of fish (Boyd & Tucker, 1998). A large number of nutrients are required to stimulate phytoplankton growth like major elements (C, N, K, P, etc.) and trace elements (Fe, Mn, Zn, etc.). Therefore, the fertilization requirement is fulfilled by adding nutrients in either organic or inorganic forms (Egna & Boyd, 1997).

Theoretically, pond fertilization is based on Liebig’s law of the minimum. The application of chemical fertilizer with manure that contains a wide C: N ratio is beneficial because the nitrogen stimulates microbial degradation of the manure. Fertilizer dissolves slowly in 3 – 4 h in standing water. Therefore, the dissolution before the application is essential. Less than 20% of phosphorus and greater than 60% of nitrogen dissolved when various solid fertilizers sank through 2 m of the water column (Boyd & Tucker, 1998).

Table 8. Fertilizer requirement in pond culture

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2.11.5 Yield and FCR

Shrestha et al . (2018) conducted two trials to evaluate the benefits of adding Nile tilapia to carp polyculture ponds. Among three separate treatments: carp+ tilapia (C + T) was one of it in which silver: bighead: common: grass: rohu: mrigal were stocked in all ponds at the ratio of 3.5:1:2:2.5:0.5:1.5:1. The gross fish yield (GFY) and net fish yield (NFY) of C+T treatment was 2.31±0.13 and 2.35 ± 0.16 respectively. The overall survival percentage in C+T treatment was 76.02±3.02. The apparent food conversion ratio (AFCR) in C+T treatment was 2.62 ± 0.17.

Pandit et al . (2018) experimented to determine the value of Nile tilapia in polyculture ponds. Among different treatments, carp (1 fish/m2): monosex-sex tilapia (3 fish/m2) was one in which silver carp, bighead carp, common carp, grass carp, rohu, and mrigal were stocked in at the ratio of 3.5:1:2.5:0.5:1.5:1. The extrapolated GFY and NFY of carp+tilapia was 3.29±0.17 and 3.20±0.17 respectively. The overall AFCR was 2.09±0.14. The gross margin per ha was 3491.9±449.5 USD.

Jha et al . (2018) evaluated different carp polyculture systems and in the treatments TF(carp + 100% feed) where silver carp, bighead carp, grass carp, common carp, rohu, and mrigal were stocked at a ratio of 4:1:4:3:5:5. The daily weight gain (g/day), and survival (%) of silver, bighead, grass, common, rohu, mrigal found to be 1.5, 65, and 2.1, 45 and 2.3, 45 and 5.1, 22 and 1.0, 66 and 0.7, 66 respectively. The overall FCR was 2.44. The overall NFY and GFY of carp only were 4.36 t/ha/yr and 4.48 t/ha/yr, respectively.

Mandal et al . (2018) assess the effect of a red algal bloom on the growth and production of carp. The fish silver: common: rohu: mrigal: bighead: grass were stocked at 3.5: 2.5: 1.5: 1:1:0.5 ratio, respectively, at the density of one fish/m2. The overall NFY and extrapolated NFY in red and non-red was 1.8 t/ha, 5.4 t/ha/yr, and 2.02 t/ha, 6.1 t/ha/yr, respectively.

Rai, Gharti, Shrestha, and Diana (2018) carried out a field trial to test substrates for periphyton enhancement in carp-SIS ponds. A control treatment without substrate which uses six carp species at 15,000 fish/ha. The carp survival in Chitwan was 40%. The combined GFY and NFY were 2.93±1.40 and 2.83±1.41 whereas FCR was 3.8.

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