Economic zoology: sericulture, apiculture and aquaculture

In short

Economic zoology is the applied study of animals that yield marketable produce — silk from moths, honey and wax from bees, fish and shellfish from water bodies. Sericulture, apiculture and aquaculture are the three largest animal-based rural enterprises in India: raw silk output is of the order of 38,000–39,000 tonnes a year (Central Silk Board, 2023-24, second after China), honey about 1.3–1.4 lakh tonnes, and total fish production roughly 175–185 lakh tonnes with inland aquaculture contributing about three-quarters. The topic is examined in B.Sc Zoology applied/economic zoology papers, in CSIR-UGC NET and ARS/ICAR life-science papers, and in recruitment for Central Silk Board, NFDB, MPEDA, state fisheries and horticulture departments, hatcheries, feed companies and shrimp exporters. Questions are mostly life cycle, rearing steps, yield arithmetic, disease management and the governing Act or regulator.

Explained

Sericulture — the silkworm and the crop

• Definition: the rearing of silkworms for cocoons and the reeling of cocoons into raw silk; moriculture is the cultivation of its food plant, mulberry (*Morus* spp., varieties V1 (Victory-1), S36, S54, G4).
• Four commercial silks in India: mulberry (*Bombyx mori*, domesticated, reeled) and three vanya (wild) silks — tasar (*Antheraea mylitta* on Asan/Arjun), oak tasar (*A. proylei*), eri (*Samia ricini* on castor; spun, not reeled, so called ahimsa silk) and muga (*A. assamensis* on Som/Soalu, golden, Assam only, a GI product).
• Voltinism: univoltine (one generation/year, temperate), bivoltine (two; finer, stronger silk) and multivoltine (many; hardy, coarser). Indian practice uses cross-breeds and bivoltine hybrids (CSR series) for better renditta.
• Life cycle (holometabolous): egg (9–12 days) → larva (5 instars, 4 moults, 24–30 days) → pupa inside cocoon (10–12 days) → adult moth (3–5 days, does not feed). Silk is secreted by a pair of modified labial (salivary) glands; the larva spins a figure-of-eight for 2–3 days.
• Fibre chemistry: fibroin (protein fibre, ~70–75%) coated with sericin gum (~25%); degumming removes sericin and the yarn loses weight accordingly.
• Rearing steps: 1) grainage — production of dfls (disease-free layings) after mother-moth examination for pebrine; 2) incubation and black-boxing for uniform hatching; 3) chawki rearing (1st–2nd instar, tender leaf, high humidity, often in a community centre); 4) late-age rearing on shoots/chopped leaf, bed cleaning and spacing; 5) mountage on chandrike/plastic collapsible mountages when larvae become translucent and stop feeding; 6) harvest after 5–6 days; 7) stifling (hot air/steam/sun) to kill the pupa, cooking, reeling (cottage basin, multi-end, automatic reeling machine), re-reeling, throwing and twisting.
• Diseases: pebrine (*Nosema bombycis*, microsporidian, transovarial — the only one controlled by mother-moth examination), flacherie (bacterial/viral gut disease), grasserie (*BmNPV*, body shines and ruptures), muscardine (*Beauveria bassiana*, white hardened larvae). Pest: uzi fly *Exorista bombycis* (use uzi traps, nylon nets, Uzicide).
• Disinfection: 2% formaldehyde or bleaching powder for the rearing house; bed disinfectants such as Vijetha/Ankush dusted on larvae; strict hygiene is the main yield lever.
• Institutions and law: Central Silk Board Act, 1948 (CSB under the Ministry of Textiles); CSRTIs at Mysuru, Berhampore, Pampore; CTRTI Ranchi, CMERTI Lahdoigarh; Silk Mark authentication; Silk Samagra-2 scheme. Karnataka is the largest raw-silk producer, followed by Andhra Pradesh, Assam, West Bengal, Tamil Nadu and Jharkhand.

Apiculture — bees, hives and products

• Definition: scientific rearing of honey bees in movable-frame hives for honey, wax and pollination; meliponiculture is stingless-bee keeping.
• Species (see table): *Apis cerana indica* (Indian hive bee, the traditional domesticated species), *A. mellifera* (Italian/European bee, highest yield, now dominant in north India), *A. dorsata* (rock bee, single open comb, migratory, not hived), *A. florea* (little bee), *Tetragonula (Trigona) iridipennis* (stingless dammer bee, excellent pollinator of small flowers).
• Colony organisation: one queen (fertile female, lays up to ~1,500–2,000 eggs/day in *mellifera*), a few hundred drones (haploid males from unfertilised eggs — arrhenotoky), and thousands of workers (sterile females doing nursing, wax building, guarding, foraging). Caste is decided by royal jelly feeding, not genetics.
• Equipment: Langstroth (for *A. mellifera*) and Newton/Jeolikote ISI hive type A and B (for *A. cerana*); frames with wax foundation, queen excluder, brood chamber and super, smoker, hive tool, veil and gloves, honey extractor, comb foundation mill, swarm/queen cage.
• Management calendar: spring build-up (give supers), honey flow (extract), dearth period (sugar-syrup 1:1 and pollen-substitute feeding), monsoon (ventilation, mould control), migratory beekeeping following mustard, sunflower, litchi, eucalyptus and coriander flows.
• Colony behaviours: swarming (reproductive split — prevent by supering, de-queening cells), absconding (whole colony leaves due to pest or dearth), supersedure (workers replace a failing queen), robbing, laying-worker colonies.
• Enemies and diseases: wax moth *Galleria mellonella*, Varroa and *Tropilaelaps* mites, Thai sacbrood virus (devastated *A. cerana* in the 1990s), European foulbrood, *Nosema*, ants, wasps, birds. Pesticide spraying during bloom is a major cause of colony loss.
• Products: honey, beeswax (about 1–2% of honey harvested), propolis, royal jelly, bee venom, bee pollen — and the largest economic benefit, pollination service (apple, almond, sunflower, mustard, coriander, onion seed).
• Standards and schemes: honey must meet the FSSAI (Food Products Standards) honey specification — broadly moisture not more than 20%, reducing sugars not less than 65%, sucrose not more than 5%, HMF not more than 80 mg/kg, with fructose/glucose ratio and C4-sugar/SMR-TMR tests for adulteration (check the current amendment, as limits have been revised); Agmark grading under the Agricultural Produce (Grading and Marking) Act, 1937; National Beekeeping and Honey Mission (NBHM, 2020) with Honey FPOs and Madhukranti traceability portal; exports through APEDA. Uttar Pradesh, Punjab, West Bengal, Bihar and Rajasthan lead production.

Aquaculture — freshwater, brackish water and mariculture

• Definition: controlled cultivation of aquatic organisms with ownership of the stock; capture fishery harvests wild stock, aquaculture inputs seed, feed and water management.
• Intensity classes: extensive (no feed, low density, <1 t/ha), semi-intensive (fertiliser + supplementary feed, 3–6 t/ha), intensive (complete feed, aeration, >10 t/ha), plus biofloc and RAS (recirculatory aquaculture system).
• Culture patterns: monoculture (shrimp, tilapia, pangasius), polyculture, and the Indian standard composite (six-species) carp culture — catla (*Labeo catla*, surface plankton), rohu (*Labeo rohita*, column), mrigal (*Cirrhinus mrigala*) and common carp (*Cyprinus carpio*) (bottom), silver carp (phytoplankton), grass carp (macrophytes); the niches are complementary so one pond yields more than any single species.
• Integrated systems: paddy-cum-fish, duck-cum-fish, poultry/pig-cum-fish, horticulture on dykes, sewage-fed culture (Kolkata bheries).
• Pond preparation: desilting; liming 200–500 kg/ha depending on soil pH; eradication of weed fish and predators (mahua oil cake 2,500 kg/ha or bleaching powder); organic manuring (raw cattle dung ~10 t/ha/year) and inorganic fertiliser (urea, single superphosphate); stocking when plankton appears (transparency 30–40 cm).
• Water-quality targets: dissolved oxygen above 5 mg/L (critical below 3), pH 7.0–8.5, un-ionised ammonia below 0.1 mg/L, nitrite low, alkalinity above 50 mg/L (shrimp 100–150), salinity 10–25 ppt for *vannamei*.
• Seed production and induced breeding: Indian major carps do not breed in confinement, so hypophysation is used — carp pituitary extract, typically a total of 6–8 mg/kg to the female in two doses (a priming dose of 2–3 mg/kg, then a resolving dose of 4–6 mg/kg six hours later) and 2–3 mg/kg to the male in a single dose given with the female's second injection, or synthetic sGnRH-a + domperidone (Ovaprim/Ovatide) at about 0.4–0.5 ml/kg for females and 0.2 ml/kg for males. Spawning follows in 4–6 hours in a Chinese circular hatchery (breeding pool + hatching pool). Stages: egg → spawn (3 days) → fry (nursery, 15 days) → fingerling (rearing pond, 2–3 months) → stocking pond.
• Brackish-water and marine: *Penaeus monodon* (tiger shrimp) and the now dominant Litopenaeus vannamei (introduced with SPF broodstock under CAA conditions), mud crab, seabass, cage culture of cobia and pompano, seaweed (*Kappaphycus*), green mussel and edible oyster farming, ornamental fish culture.
• Diseases: white spot syndrome virus (WSSV), EHP, running mortality syndrome, vibriosis and white faeces in shrimp; EUS (epizootic ulcerative syndrome), argulosis, dropsy, ich and columnaris in carps; TiLV in tilapia. Management is biosecurity, quality seed, probiotics and water exchange — antibiotics such as chloramphenicol and nitrofurans are banned in aquaculture for export.
• Law, regulators, schemes: Coastal Aquaculture Authority Act, 2005 (registration of coastal farms; the Amendment Act, 2023 brought hatcheries, broodstock-multiplication and nucleus-breeding centres into its scope and eased penalties); CAA and MPEDA/NaCSA for pre-harvest testing and export certification; NFDB Hyderabad; PMMSY (2020, total outlay of about ₹20,050 crore, of which the central share is about ₹9,407 crore) and the earlier Blue Revolution; FIDF credit; ICAR institutes CIFA Bhubaneswar, CIFRI Barrackpore, CIBA Chennai, CMFRI Kochi, CIFE Mumbai, CIFT Kochi. Andhra Pradesh is by far the largest producer, then West Bengal, Gujarat, Odisha, Tamil Nadu and Kerala.

Economics and quality grading, sector by sector

• Sericulture income is per crop (5–6 crops/year in south India) and hinges on renditta — cocoon kilograms needed per kilogram of raw silk; lower is better (bivoltine 6–7, multivoltine 8–9).
• Raw silk is graded (4A/3A/2A/A, etc.) on evenness, cleanness, neatness and tenacity; finer denier fetches more.
• Honey price depends on moisture, colour, flora (mono-floral mustard, litchi, jamun) and absence of C4 sugars; export rejection is usually for antibiotic residue or adulteration.
• Shrimp is priced by count (pieces per kg): 30 g animals are about 33 count; a *lower* count (fewer, bigger animals per kg) earns more per kg, so farmers trade off a longer crop against disease risk.
• All three are seasonal and price-volatile; quoted prices below are indicative and change with the market.

Key points

• Moriculture - cultivation of mulberry; leaf quality decides cocoon weight, so about 60–65% of sericulture cost is leaf production.
• dfl - disease-free laying, one moth's egg batch (~400–500 eggs), the unit in which worms are bought and yield is quoted (kg cocoons per 100 dfls).
• Chawki rearing - young-age (1st–2nd instar) rearing in controlled humidity; most crop failures trace back to it.
• Pebrine - *Nosema bombycis*, transmitted through the egg; prevented only by mother-moth examination at grainage.
• Renditta - kg of cocoons per kg of raw silk; raw silk recovery % = 100/renditta.
• Shell ratio - cocoon shell weight as % of whole cocoon weight; 20–25% in good bivoltines, the best single predictor of silk yield.
• Sericin and fibroin - gum and fibre of silk; degumming removes about a quarter of the weight.
• Vanya silks - tasar, oak tasar, eri and muga; eri is spun because the moth is allowed to emerge, muga is exclusive to Assam.
• Caste determination in bees - royal jelly feeding, not genes; drones are haploid from unfertilised eggs.
• Swarming vs absconding - a reproductive split leaving a queen cell behind, versus total desertion of the hive.
• Queen excluder - grid that keeps the queen out of the super so honey combs stay brood-free.
• Composite fish culture - six species in complementary feeding niches; 4–6 t/ha/year with manure and supplementary feed.
• Hypophysation - induced breeding with pituitary extract or sGnRH-a + domperidone, since IMCs do not breed in ponds.
• FCR - feed given per kg of weight gained; 1.3–1.6 in good shrimp crops, 1.5–2.0 in fed carp culture.
• Stocking density - 5,000 fingerlings/ha for composite carp; 30–60 post-larvae/m² for semi-intensive *vannamei*.
• Dissolved oxygen - must stay above 5 mg/L; dawn is the daily minimum, hence paddle-wheel aeration at night.
• CAA registration - compulsory for coastal aquaculture farms; the 2023 amendment extended it to hatcheries and nucleus breeding centres.
• Banned inputs - chloramphenicol, nitrofurans and other listed antibiotics in aquaculture; residues cause export consignment rejection.

Formulas and examples

1. Sericulture crop and renditta. A farmer with one acre of V1 mulberry brushes 300 dfls per crop, 5 crops a year, and gets 65 kg cocoons per 100 dfls.

• Cocoons per crop = 65 × 300/100 = 195 kg; annual = 195 × 5 = 975 kg.
• At renditta 6.5, raw silk = 975/6.5 = 150 kg; recovery = 100/6.5 = 15.4%.
• Cocoon price ₹450/kg (varies with market and grade) → gross ₹450 × 975 = ₹4,38,750/year.
• If better hygiene cuts renditta to 6.0, the same cocoons give 975/6.0 = 162.5 kg silk — 12.5 kg extra silk for no extra leaf.

2. Shell ratio and denier. A cocoon weighs 1.80 g, its shell 0.42 g; a reeled filament 900 m long weighs 0.25 g.

• Shell ratio = (0.42/1.80) × 100 = 23.3% (good bivoltine).
• Denier = (0.25 × 9,000)/900 = 2.5 denier per single filament.
• To reel a 20/22 denier raw silk thread (take 21), cocoons needed together = 21/2.5 ≈ 8 cocoons.

3. Apiculture enterprise. 50 *A. mellifera* colonies yielding 30 kg honey each per year.

• Honey = 50 × 30 = 1,500 kg; at ₹180/kg (bulk, indicative) = ₹2,70,000.
• Beeswax at 1.5% of honey = 22.5 kg; at ₹400/kg = ₹9,000.
• If dearth-period feeding costs 4 kg sugar per colony at ₹45/kg = 50 × 4 × 45 = ₹9,000, it is recovered by ~50 kg of extra honey.

4. Composite carp culture, 1 ha. Stocked 5,000 fingerlings of 20 g each; survival 85%; average harvest weight 750 g; supplementary feed (rice bran + groundnut cake) 4,500 kg used.

• Harvested number = 0.85 × 5,000 = 4,250 fish; standing crop = 4,250 × 0.750 = 3,187.5 kg.
• Stocked biomass = 5,000 × 0.020 = 100 kg → net yield = 3,187.5 − 100 = 3,087.5 kg/ha/year.
• FCR = 4,500/3,087.5 = 1.46; FCE = 100/1.46 ≈ 68%.
• At ₹120/kg, gross = 3,187.5 × 120 = ₹3,82,500/ha.

5. *L. vannamei* semi-intensive crop, 1 ha. 40 PL/m² stocked and nursery-reared to ~1 g before release into the grow-out pond (a hatchery PL10 itself weighs only about 2 mg), 110 days, survival 85%, harvest average body weight 30 g, feed consumed 15.3 t.

• Seed stocked = 40 × 10,000 = 4,00,000; harvested = 0.85 × 4,00,000 = 3,40,000.
• Biomass = 3,40,000 × 0.030 = 10,200 kg = 10.2 t/ha/crop; count = 1,000/30 ≈ 33 pieces per kg.
• Stocked biomass = 4,00,000 × 0.001 = 400 kg → gain = 10,200 − 400 = 9,800 kg; FCR = 15,300/9,800 = 1.56.
• SGR = [(ln 30 − ln 1)/110] × 100 = (3.4012/110) × 100 = 3.09% per day; ADG = (30 − 1)/110 = 0.26 g/day.
• At ₹320/kg for 33 count (farm-gate prices move weekly), gross = 10,200 × 320 = ₹32,64,000 per crop.

Where it is used

• Silk value chain: Central Silk Board and CSRTIs, state sericulture departments, grainages, chawki rearing centres, cocoon markets (Ramanagara, Siddlaghatta), reeling and twisting units, silk weaving clusters (Kanchipuram, Varanasi, Bhagalpur, Sualkuchi) — roles as sericulture inspector, technical assistant, silk reeling supervisor, Silk Mark auditor.
• Honey and pollination: NBHM/NAFED honey FPOs, Dabur, Patanjali, Apis India and Kashmir Apiaries procurement, migratory beekeeping contracts with apple and mustard growers, bee-breeding and equipment units — roles in quality control (moisture, HMF, C4 testing) and extension.
• Freshwater aquaculture: carp and pangasius farms in Andhra Pradesh, Kolleru belt, West Bengal bheries, Chhattisgarh and Odisha reservoir ranching; hatcheries doing induced breeding; NFDB and state fisheries projects; roles as farm manager, hatchery technician, aqua-feed sales and nutritionist.
• Brackish water and export: shrimp farms and feed mills (CP Aquaculture, Avanti, Growel), MPEDA/NaCSA aqua-labs for pre-harvest antibiotic and WSSV PCR testing, processing and export plants in Nellore, Bhimavaram, Surat and Kochi.
• Research, teaching and regulation: ICAR institutes (CIFA, CIBA, CMFRI, CIFE, CIFT), CAA registration and inspection, FSSAI and APEDA compliance, bank and NABARD appraisal of sericulture, bee and fish-pond loans.
• Rural livelihood programmes: farm-pond works under the rural employment guarantee (MGNREGA, replaced from 1 July 2026 by the VB-G RAM G Act, 2025), PMMSY beneficiary schemes, KVIC and KVK training in beekeeping and vermi/fish integration, self-help group ornamental fish and mushroom-plus-apiary models.

Interview questions

• Q: Why is mother-moth examination done in a grainage? A: To detect *Nosema bombycis* (pebrine), which passes through the egg; infected moths' layings are destroyed so only disease-free layings (dfls) go to farmers.
• Q: What is renditta and what does a value of 6.5 mean? A: The cocoon weight needed per kg of raw silk; 6.5 means 6.5 kg of cocoons give 1 kg of silk, i.e. 15.4% recovery.
• Q: Why is eri called ahimsa silk and why can it not be reeled? A: The moth is allowed to emerge, so the continuous filament is broken; the open cocoon is degummed and spun into yarn.
• Q: Which silk is produced only in Assam and on which host plants? A: Muga, from *Antheraea assamensis* reared on Som (*Persea bombycina*) and Soalu; it has a GI tag.
• Q: How is caste determined in a honey bee colony? A: By larval feeding — a larva fed royal jelly throughout becomes a queen, a female fed worker jelly becomes a worker; drones develop from unfertilised eggs.
• Q: Difference between swarming and absconding? A: In swarming the colony divides and half leaves with the old queen, leaving brood and a queen cell; in absconding the entire colony deserts the hive, usually from dearth, mites or disturbance.
• Q: Why is *Apis mellifera* preferred commercially over *A. cerana indica*? A: Larger colonies, less swarming, gentler behaviour and three to four times the honey yield; but it is exotic, needs more feeding and is Varroa-susceptible.
• Q: Why is composite fish culture more productive than monoculture of rohu? A: The six species feed at different levels — surface plankton, column, bottom detritus, phytoplankton and macrophytes — so the pond's full food web is harvested without competition.
• Q: What is hypophysation and why is it needed? A: Injecting pituitary extract or sGnRH-a with domperidone to trigger ovulation, because Indian major carps will not spawn in confined ponds without the riverine flood stimulus.
• Q: A shrimp pond shows an FCR of 2.2. What are the likely causes? A: Overfeeding or poor feed management, low survival that is not yet visible, poor water quality or disease suppressing growth, or wet/spoiled feed — check feed trays, survival estimate and DO first.
• Q: Which approvals does a new coastal shrimp farm need? A: Registration with the Coastal Aquaculture Authority under the CAA Act, 2005 (as amended in 2023), CRZ compliance, and for export, MPEDA registration with pre-harvest antibiotic testing.
• Q: Why is dissolved oxygen lowest just before dawn? A: Photosynthesis stops at night while fish, plankton and sediment keep respiring, so oxygen falls through the dark hours and bottoms out at sunrise — hence night aeration.

Common mistakes

• Inverting renditta — writing raw silk per kg of cocoons; and forgetting that lower renditta is better.
• Calling eri and muga "mulberry silks", or saying all four silks are reeled (eri is spun).
• Confusing pebrine with flacherie or grasserie, or claiming disinfectants cure pebrine.
• Saying royal jelly is fed only to the queen larva — all larvae get it for the first few days; the queen keeps getting it.
• Treating *A. dorsata* as a hive species, or quoting its wild yield as achievable from a managed colony.
• Computing FCR against the harvested biomass instead of the gain (harvest minus stocked weight), which flatters the figure.
• Quoting shrimp or fish yield without the area, stocking density or crop duration — a denominator-free "10 tonnes" means nothing.
• Writing stocking density per hectare and per m² interchangeably (1 ha = 10,000 m²), which shifts the answer by four orders of magnitude.

Related topics

Animal behaviour · Parasitology · Wildlife conservation · Zoology careers · Entomology and insect morphology · Fish biology and physiology