I85PREP
⌘ K
WBCHSE HS Fisheries study materials
WBCHSE HS Fisheries study resources

WBCHSE HS Fisheries practice questions

One question at a time. Build your WBCHSE HS Fisheries understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Introduction to Fisheries and Aquaculture: scope, sector status in West Bengal and India, capture vs culture fisheries, terminology

In fisheries terminology, the general term for the controlled rearing of aquatic organisms - fish, molluscs, crustaceans and aquatic plants - is:

  1. Hatching
  2. Fish curing
  3. Capture fishery
  4. Aquaculture Correct answer.

Explanation

Aquaculture is the controlled rearing of aquatic organisms, including fish, crustaceans, molluscs and aquatic plants, in managed water bodies. Capture fishery, by contrast, depends on harvesting naturally recruited wild stocks rather than on planned stocking and feeding.

Question 2Introduction to Fisheries and Aquaculture: scope, sector status in West Bengal and India, capture vs culture fisheries, terminology

West Bengal's nationally recognised strength in fish production lies mainly in:

  1. Marine seaweed harvesting
  2. Deep-sea tuna longlining
  3. Cold-water trout ranching
  4. Inland freshwater aquaculture Correct answer.

Explanation

West Bengal is one of India's leading inland fish producers, with extensive pond, tank and canal-based freshwater culture, and it also supplies fish seed to other states. Its coastline supports marine fishing, but that is not the state's defining strength in national fisheries statistics.

Question 3Introduction to Fisheries and Aquaculture: scope, sector status in West Bengal and India, capture vs culture fisheries, terminology

In hatchery and pond management, the term 'fish seed' refers to:

  1. Spawn, fry and fingerlings for stocking ponds Correct answer.
  2. Waste fish parts ground into meal for animal feed
  3. Fish that have been preserved by drying and salting
  4. Mature brood fish kept separately only for breeding purposes

Explanation

Fish seed is the collective term for spawn, fry and fingerlings produced in hatcheries or nurseries and stocked into rearing ponds. It is the input that determines stocking density and, therefore, the expected yield of a culture system.

Question 4Introduction to Fisheries and Aquaculture: scope, sector status in West Bengal and India, capture vs culture fisheries, terminology

Which statement correctly distinguishes culture fisheries from capture fisheries?

  1. Culture involves deliberate stocking and management Correct answer.
  2. Capture fisheries always use formulated feed
  3. Both depend entirely on natural recruitment of juveniles
  4. Both are practised only in marine waters

Explanation

In culture fisheries the farmer stocks seed, feeds the fish and manages water quality, so the harvest is planned rather than left to natural recruitment. Capture fisheries, in contrast, take fish from self-recruiting wild stocks, and management there focuses on regulating gear and fishing effort.

Question 5Introduction to Fisheries and Aquaculture: scope, sector status in West Bengal and India, capture vs culture fisheries, terminology

In global fish production, India is generally placed second, behind which country?

  1. Norway
  2. Japan
  3. China Correct answer.
  4. Brazil

Explanation

China is the world's largest fish producer, and India occupies the second position in global fish production, with inland aquaculture and marine capture both contributing substantially. India is likewise the second largest aquaculture producer after China.

Question 6Introduction to Fisheries and Aquaculture: scope, sector status in West Bengal and India, capture vs culture fisheries, terminology

Which list best represents the scope of the fisheries sector as studied in fisheries science?

  1. Only marine fishing by mechanised trawlers
  2. Capture, culture, processing and marketing Correct answer.
  3. Only pond farming of freshwater carps
  4. Only the catching of wild fish from rivers

Explanation

Fisheries as a discipline and industry covers harvesting, farming, handling, processing, value addition, by-product utilisation and marketing. Narrow descriptions such as catching alone or pond farming alone leave out major segments of the sector and its employment.

Question 7Introduction to Fisheries and Aquaculture: scope, sector status in West Bengal and India, capture vs culture fisheries, terminology

In a fish hatchery, 'brood stock' means:

  1. Fish reared purely for ornamental display
  2. Small fish used as live bait in capture fishing
  3. Mature fish kept for breeding Correct answer.
  4. Fish graded and packed for retail sale

Explanation

Brood stock are sexually mature fish selected and maintained under good nutrition and water quality so that they can breed naturally or be induced to breed in hatcheries. Their quality directly influences the quantity and quality of seed produced.

Question 8Introduction to Fisheries and Aquaculture: scope, sector status in West Bengal and India, capture vs culture fisheries, terminology

Which of the following is an exotic carp widely used in Indian composite fish culture?

  1. Grass carp Correct answer.
  2. Mrigal
  3. Catla
  4. Rohu

Explanation

Grass carp, silver carp and common carp are exotic Chinese carps introduced into India, whereas catla, rohu and mrigal are the Indian major carps. Composite fish culture combines both groups so that food available at different pond levels is used efficiently.

Question 9Introduction to Fisheries and Aquaculture: scope, sector status in West Bengal and India, capture vs culture fisheries, terminology

A fishery in which the stock is harvested by many operators, no one owns the fish until they are caught, and management depends on limiting licences, gear or season is best described as:

  1. A hatchery-based seed unit
  2. An open-access capture fishery Correct answer.
  3. A recirculating aquaculture system
  4. A monoculture pond farm

Explanation

An open-access capture fishery is one in which no individual or group owns the stock, so fishers compete for a common resource and management must be achieved by restricting licences, gear, season or catch. Pond farms, hatcheries and recirculating systems all have defined owners and stocked populations, so they are not open-access fisheries.

Question 10Introduction to Fisheries and Aquaculture: scope, sector status in West Bengal and India, capture vs culture fisheries, terminology

In a six-species composite fish culture pond, which species is stocked mainly to control submerged and floating aquatic weeds?

  1. Rohu
  2. Grass carp Correct answer.
  3. Mrigal
  4. Catla

Explanation

Grass carp is a herbivorous feeder that consumes aquatic macrophytes, so it is stocked to keep weeds in check and convert them into fish flesh. Catla feeds on zooplankton in the surface layer, rohu is a mid-water column feeder and mrigal feeds on bottom detritus, so none of these three controls weeds.

Question 11Introduction to Fisheries and Aquaculture: scope, sector status in West Bengal and India, capture vs culture fisheries, terminology

Which of the following sets consists only of Indian major carps?

  1. Mrigal, silver carp and common carp
  2. Catla, rohu and mrigal Correct answer.
  3. Grass carp, silver carp and common carp
  4. Rohu, catla and grass carp

Explanation

Indian major carps are the three native riverine carps - catla (Catla catla), rohu (Labeo rohita) and mrigal (Cirrhinus mrigala). Grass carp, silver carp and common carp are exotic species introduced from outside India and are not classified as Indian major carps.

Question 12Introduction to Fisheries and Aquaculture: scope, sector status in West Bengal and India, capture vs culture fisheries, terminology

In Indian fisheries, the term 'Blue Revolution' refers to:

  1. licensing of foreign vessels for deep-sea fishing
  2. a planned programme to expand fish and aquaculture production Correct answer.
  3. cold-chain development for marine fish only
  4. a programme for coral reef conservation in tropical coastal waters

Explanation

The Blue Revolution refers to India's planned strategy, launched in the mid-1980s, to raise fish and aquaculture production through extension support, hatchery development and pond-based culture. It is not a coral-reef, foreign-vessel licensing or marine cold-chain programme.

Question 13Introduction to Fisheries and Aquaculture: scope, sector status in West Bengal and India, capture vs culture fisheries, terminology

Rearing a single species of fish in a pond to the exclusion of all other species is known as:

  1. Mixed culture
  2. Polyculture
  3. Monoculture Correct answer.
  4. Composite fish culture

Explanation

Monoculture means rearing only one species in a pond, so all stocked fish share the same food and space niche. Polyculture, mixed culture and composite fish culture all involve several species together and are therefore not single-species systems.

Question 14Introduction to Fisheries and Aquaculture: scope, sector status in West Bengal and India, capture vs culture fisheries, terminology

In carp seed terminology, a 'fingerling' is best described as:

  1. a young fish of about 75–100 mm in length Correct answer.
  2. a newly hatched larva still carrying its yolk sac
  3. a fry of about 20–25 mm reared for a few days
  4. a post-larva of about 10 mm before stocking

Explanation

Carp seed is graded by size: spawn is the newly hatched larva, fry are small post-larvae of about 20–25 mm, and fingerlings are 75–100 mm long and finger-like. A fingerling is therefore the advanced stage used for stocking grow-out ponds.

Question 15Introduction to Fisheries and Aquaculture: scope, sector status in West Bengal and India, capture vs culture fisheries, terminology

The East Kolkata Wetlands are internationally recognised for which fisheries practice?

  1. Sewage-fed fish culture using treated wastewater Correct answer.
  2. Hatchery production of ornamental fish
  3. Cage culture of tilapia in saline water
  4. Deep-sea trawling for tuna and other oceanic fish

Explanation

The East Kolkata Wetlands are a Ramsar site where the city's sewage is treated naturally in a network of ponds and the nutrient-rich water is used for fish culture. This wastewater-fed aquaculture is a recognised West Bengal speciality, not deep-sea trawling, saline cage culture or ornamental hatchery work.

Question 16Introduction to Fisheries and Aquaculture: scope, sector status in West Bengal and India, capture vs culture fisheries, terminology

In the Sundarbans region of West Bengal, a 'bheri' is:

  1. a bunded brackishwater pond for fish and prawn Correct answer.
  2. a cold store for dried marine fish
  3. a freshwater hatchery used for Indian major carp seed
  4. a cast net used for catching estuarine hilsa

Explanation

Bheris are traditional brackishwater impoundments in the Sundarbans, enclosed by earthen bunds, where tidal water is let in and fish and prawns are cultured or trapped. They are distinct from freshwater carp hatcheries, cast nets and dried-fish cold stores.

Question 17Introduction to Fisheries and Aquaculture: scope, sector status in West Bengal and India, capture vs culture fisheries, terminology

Integrated fish farming is best described as:

  1. rearing a single fish species at very high stocking density
  2. using only formulated feed and no pond manure
  3. harvesting wild fish from rivers and estuaries
  4. combining fish culture with crop or livestock farming Correct answer.

Explanation

Integrated fish farming links pond culture with another farm enterprise, such as poultry, piggery, horticulture or rice, so that wastes and by-products become pond inputs. This recycling lowers feed and fertiliser costs; it is not monoculture, wild capture or a feed-only system.

Question 18Introduction to Fisheries and Aquaculture: scope, sector status in West Bengal and India, capture vs culture fisheries, terminology

The giant freshwater prawn, Macrobrachium rosenbergii, is commonly marketed in India under which name?

  1. Scampi Correct answer.
  2. Tiger prawn
  3. Hilsa
  4. Mrigal

Explanation

Macrobrachium rosenbergii is the giant freshwater prawn, sold in Indian markets as scampi. Penaeus monodon is the brackishwater tiger prawn, while hilsa is a fish and mrigal is a carp.

Question 19Introduction to Fisheries and Aquaculture: scope, sector status in West Bengal and India, capture vs culture fisheries, terminology

Which of the following is an example of a capture fishery in West Bengal?

  1. A carp hatchery on the Kangsabati river
  2. Sewage-fed carp ponds of the East Kolkata Wetlands
  3. A bheri in the Sundarbans stocked with prawn seed
  4. Hilsa fishery of the Hooghly estuary Correct answer.

Explanation

A capture fishery relies on naturally recruited wild stock that is caught without stocking or feeding by the operator. The Hooghly hilsa fishery fits this, whereas sewage-fed ponds, stocked bheris and hatcheries are culture-based systems.

Question 20Introduction to Fisheries and Aquaculture: scope, sector status in West Bengal and India, capture vs culture fisheries, terminology

Why can the yield of a capture fishery not be raised indefinitely by increasing fishing effort?

  1. because recruitment and growth limit sustainable yield Correct answer.
  2. because wild fish do not accept formulated feed
  3. because fishing gear becomes less effective with each season
  4. because captured fish have no market value

Explanation

In a capture fishery, production depends on natural recruitment, growth and mortality, and the stock can sustain only a limited harvest called the maximum sustainable yield. Fishing beyond this level reduces the spawning stock and future recruitment, so extra effort lowers rather than raises the catch.

Question 21Fish Biology, Taxonomy and Identification: external morphology, fin formula, scales, major freshwater and brackishwater species of the region

In a fin formula such as D. XI–XIII, 14–16, what does the Roman numeral section (XI–XIII) represent?

  1. The total number of rays in the dorsal fin
  2. The number of unbranched spinous rays in the dorsal fin Correct answer.
  3. The number of branched soft rays in the dorsal fin
  4. The number of scales along the lateral line

Explanation

By convention, Roman numerals in a fin formula count the unsegmented, unbranched spinous rays, while the Arabic numerals after the comma count the branched soft rays. Thus XI–XIII means 11 to 13 dorsal spines, and 14–16 means 14 to 16 soft rays.

Question 22Fish Biology, Taxonomy and Identification: external morphology, fin formula, scales, major freshwater and brackishwater species of the region

Which accessory respiratory structure allows Anabas testudineus to survive for hours out of water?

  1. Swim bladder
  2. Labyrinthine organ Correct answer.
  3. Suprabranchial air sac
  4. Arborescent organ

Explanation

Anabas testudineus, the climbing perch, possesses a labyrinthine organ in the suprabranchial chamber that absorbs atmospheric oxygen. This is why the fish can breathe air and remain alive outside water for long periods.

Question 23Fish Biology, Taxonomy and Identification: external morphology, fin formula, scales, major freshwater and brackishwater species of the region

The lateral line of a teleost fish is primarily concerned with which function?

  1. Grinding food before it reaches the stomach
  2. Secreting mucus to protect the body surface
  3. Maintaining neutral buoyancy in the water column
  4. Detecting water currents and low-frequency vibrations Correct answer.

Explanation

The lateral line is a sense-organ system of neuromasts that detects water movements, pressure changes and low-frequency vibrations. It helps the fish in schooling, predator avoidance and orientation in currents.

Question 24Fish Biology, Taxonomy and Identification: external morphology, fin formula, scales, major freshwater and brackishwater species of the region

Which freshwater fish of West Bengal possesses a fleshy, ray-less adipose fin between the dorsal fin and the caudal fin?

  1. Labeo rohita
  2. Mystus vittatus Correct answer.
  3. Clarias batrachus
  4. Channa punctatus

Explanation

An adipose fin is a small, fleshy, ray-less fin located behind the dorsal fin, and it is characteristic of many bagrid catfishes such as Mystus vittatus. Labeo rohita, Clarias batrachus and Channa punctatus do not have an adipose fin.

Question 25Fish Biology, Taxonomy and Identification: external morphology, fin formula, scales, major freshwater and brackishwater species of the region

How many pairs of barbels are normally present in Clarias batrachus?

  1. Two pairs
  2. Five pairs
  3. Three pairs
  4. Four pairs Correct answer.

Explanation

Clarias batrachus bears four pairs of barbels: nasal, maxillary, inner mandibular and outer mandibular. These long tactile barbels help the walking catfish locate food in turbid, oxygen-poor water.

Question 26Fish Biology, Taxonomy and Identification: external morphology, fin formula, scales, major freshwater and brackishwater species of the region

Catla catla is placed in the surface-feeding zone of a composite carp pond mainly because its mouth is

  1. subterminal with thick fleshy lips
  2. inferior and sucker-like
  3. terminal and horizontally directed
  4. superior and upturned Correct answer.

Explanation

Catla catla has a large head with an upturned, superior mouth, which adapts it to feed on plankton at the water surface. This mouth orientation is the main morphological reason for its surface-feeding habit in composite culture.

Question 27Fish Biology, Taxonomy and Identification: external morphology, fin formula, scales, major freshwater and brackishwater species of the region

Channa punctatus is classified under which family?

  1. Bagridae
  2. Clariidae
  3. Cyprinidae
  4. Channidae Correct answer.

Explanation

Channa punctatus, the spotted snakehead, belongs to the family Channidae. Its elongated body, long dorsal and anal fins, and accessory air-breathing habit are characteristic of this family.

Question 28Fish Biology, Taxonomy and Identification: external morphology, fin formula, scales, major freshwater and brackishwater species of the region

Which regional fish is anadromous, spending most of its life in the sea but migrating up rivers to breed?

  1. Catla catla
  2. Tenualosa ilisha Correct answer.
  3. Labeo rohita
  4. Mugil cephalus

Explanation

Tenualosa ilisha, the Indian shad or hilsa, is anadromous: adults live in coastal waters and migrate upstream in rivers to spawn. Labeo and Catla are freshwater carps, while Mugil cephalus is catadromous rather than anadromous.

Question 29Fish Biology, Taxonomy and Identification: external morphology, fin formula, scales, major freshwater and brackishwater species of the region

A cyprinid from a West Bengal pond has two pairs of barbels, a dorsal fin with 12–14 branched rays, and cycloid scales. It is the most extensively cultured Indian major carp. Identify the fish.

  1. Catla catla
  2. Labeo rohita Correct answer.
  3. Cirrhinus mrigala
  4. Cyprinus carpio

Explanation

Labeo rohita, the rohu, is identified by two pairs of barbels, a dorsal fin with about 12–14 branched rays and cycloid scales. Catla lacks barbels and has an upturned mouth, while Cirrhinus mrigala has only one pair of barbels.

Question 30Fish Biology, Taxonomy and Identification: external morphology, fin formula, scales, major freshwater and brackishwater species of the region

Which fish–scale type pairing is correct?

  1. Catla catla – ctenoid scales
  2. Labeo rohita – ctenoid scales
  3. Lates calcarifer – ctenoid scales Correct answer.
  4. Mugil cephalus – placoid scales

Explanation

Ctenoid scales have tiny comb-like ctenii on their posterior margin and occur in higher teleosts such as Lates calcarifer. Carps like Labeo and Catla and mullets like Mugil have cycloid scales, while placoid scales occur only in elasmobranchs.

Question 31Fish Biology, Taxonomy and Identification: external morphology, fin formula, scales, major freshwater and brackishwater species of the region

In the fin system of a teleost fish such as Labeo rohita, which pair of fins constitutes the paired fins?

  1. Dorsal and anal fins
  2. Caudal and anal fins
  3. Pectoral and pelvic fins Correct answer.
  4. Dorsal and adipose fins

Explanation

Paired fins are the pectoral and pelvic fins, one of each on either side of the body; they are serially homologous with the limbs of land vertebrates. Dorsal, caudal, anal and adipose fins are median, unpaired fins because they lie on the mid-line.

Question 32Fish Biology, Taxonomy and Identification: external morphology, fin formula, scales, major freshwater and brackishwater species of the region

Which fish of the Sundarbans estuarine region is a brackishwater species that supports a valued capture fishery?

  1. Lates calcarifer Correct answer.
  2. Labeo rohita
  3. Wallago attu
  4. Clarias batrachus

Explanation

Lates calcarifer, the beckti or barramundi, is a large perch-like fish of estuaries, coastal lagoons and tidal rivers and is a well-known brackishwater food fish of coastal West Bengal. The other three species are freshwater fishes of ponds, tanks and rivers.

Question 33Fish Biology, Taxonomy and Identification: external morphology, fin formula, scales, major freshwater and brackishwater species of the region

The caudal fin of an advanced teleost such as Labeo rohita is best described as:

  1. Homocercal, with externally symmetrical lobes and the vertebral column ending at the fin base Correct answer.
  2. Heterocercal, with the vertebral column running into the larger upper lobe
  3. Diphycercal, with the vertebral column running straight to the tip of the fin
  4. Hypocercal, with the lower lobe markedly larger than the upper lobe

Explanation

In a homocercal tail the two lobes look externally equal and the vertebral axis stops at the base of the fin, which is the usual condition in advanced bony fishes such as carps. A heterocercal tail, in which the axis bends into the larger upper lobe, is typical of sharks.

Question 34Fish Biology, Taxonomy and Identification: external morphology, fin formula, scales, major freshwater and brackishwater species of the region

In a bottom-dwelling catfish such as Clarias batrachus, the barbels around the mouth are chiefly useful because they:

  1. Bear taste buds and help in locating food in turbid water Correct answer.
  2. Support the body against the muddy bottom while the fish rests
  3. Act as accessory respiratory organs in stagnant water
  4. Detect pressure waves made by distant swimming prey

Explanation

Barbels are fleshy, taste-bud-bearing appendages around the mouth that allow a nocturnal, bottom-dwelling catfish to sample mud and water for food in darkness or turbidity. They are sensory structures and take no part in respiration or in propping up the body.

Question 35Fish Biology, Taxonomy and Identification: external morphology, fin formula, scales, major freshwater and brackishwater species of the region

Fishery biologists estimate the age of a carp by counting annuli on its scales. These annuli are:

  1. Fine spines (ctenii) arranged along the posterior margin of the scale
  2. Concentric growth rings formed when growth slows during a poor-feeding season Correct answer.
  3. Radiating grooves that mark the course of the lateral-line canal
  4. The first-formed central focus of the scale, laid down in the fry stage

Explanation

A scale grows faster in the favourable season and slowly in the poor season, so each year's growth leaves a concentric band whose boundary with the next band is an annulus. Counting these rings gives an estimate of the fish's age, a standard technique in carp fishery biology.

Question 36Fish Biology, Taxonomy and Identification: external morphology, fin formula, scales, major freshwater and brackishwater species of the region

Cirrhinus mrigala is placed in the bottom-feeding zone of a composite carp pond. Its mouth is best described as:

  1. Superior, with an upturned lower jaw
  2. Inferior, directed downwards beneath a blunt snout Correct answer.
  3. Tubular and protrusible, used for sucking insects
  4. Terminal, with the two jaws meeting in front

Explanation

An inferior, downward-directed mouth allows mrigal to graze on algae, detritus and bottom organisms, which is why it is grouped with the bottom feeders in composite carp culture. A superior or terminal mouth belongs to surface- and column-feeding fishes.

Question 37Fish Biology, Taxonomy and Identification: external morphology, fin formula, scales, major freshwater and brackishwater species of the region

A greyish mullet taken from a brackishwater bheri has two short dorsal fins placed far apart, a small mouth, and a dark bluish spot at the base of the pectoral fin. The species is:

  1. Tenualosa ilisha
  2. Mugil cephalus Correct answer.
  3. Lates calcarifer
  4. Chanos chanos

Explanation

Mugil cephalus, the grey mullet, is recognised by two widely separated short dorsal fins, a small mouth and a bluish spot at the pectoral-fin base, and it is a common fish of coastal bheris and estuaries. The combination of two dorsal fins and the pectoral spot separates it from the other species listed.

Question 38Fish Biology, Taxonomy and Identification: external morphology, fin formula, scales, major freshwater and brackishwater species of the region

The Weberian apparatus, a chain of modified anterior vertebrae linking the swim bladder to the inner ear, is present in:

  1. Channa striata
  2. Lates calcarifer
  3. Tenualosa ilisha
  4. Labeo rohita Correct answer.

Explanation

The Weberian apparatus transmits vibrations from the swim bladder to the inner ear and thus sharpens hearing, and it is a defining character of the Ostariophysi. Carps such as Labeo rohita and catfishes belong to this group, whereas clupeids, channids and latids do not possess it.

Question 39Fish Biology, Taxonomy and Identification: external morphology, fin formula, scales, major freshwater and brackishwater species of the region

A fish landed at a Hooghly estuary landing centre has placoid scales, five pairs of gill slits, and a heterocercal caudal fin with the vertebral column running into the upper lobe. It should be placed in:

  1. Osteichthyes, because its scales are dermal plates like those of a carp
  2. Holocephali, because placoid scales occur only in chimaeras and not in sharks
  3. Dipnoi, because a heterocercal tail is typical of lungfishes
  4. Chondrichthyes (Elasmobranchii), because all three features are elasmobranch characters Correct answer.

Explanation

Placoid scales, exposed gill slits in five pairs and a heterocercal caudal fin are classic elasmobranch characters, so the specimen is a cartilaginous fish such as a shark or ray. Bony fishes normally have cycloid or ctenoid scales, a single gill opening covered by an operculum, and a homocercal tail.

Question 40Fish Biology, Taxonomy and Identification: external morphology, fin formula, scales, major freshwater and brackishwater species of the region

Labeo rohita is placed in the family Cyprinidae. In the standard classification of bony fishes, the rank immediately above family that contains this species is:

  1. Teleostei
  2. Cypriniformes Correct answer.
  3. Actinopterygii
  4. Ostariophysi

Explanation

In the Linnaean hierarchy the order stands directly above the family, and the carp family Cyprinidae belongs to the order Cypriniformes. Actinopterygii, Teleostei and Ostariophysi are all higher categories placed above the level of the order.

Question 41Pond Construction, Soil and Water Quality Management: site selection, pond types, liming, fertilization, dissolved oxygen, pH, ammonia

A farmer in the Gangetic plains wants to dig a pond that will retain water throughout the year. Which pond-bottom soil is the most suitable for this purpose?

  1. Coarse sand with a high percolation rate
  2. Gravel mixed with pebbles and stones
  3. Fissured rocky subsoil
  4. Clayey loam Correct answer.

Explanation

A pond bottom must hold water, so a soil with an adequate clay fraction is preferred. Clayey loam has enough clay to seal the pores, yet it can still be worked and does not crack as severely as pure clay. Sandy, gravelly and fissured rocky soils allow rapid seepage, making filling uneconomic.

Question 42Pond Construction, Soil and Water Quality Management: site selection, pond types, liming, fertilization, dissolved oxygen, pH, ammonia

In composite fish culture, the small shallow pond in which spawn is reared up to the fry stage is called a

  1. production pond
  2. stocking pond
  3. rearing pond
  4. nursery pond Correct answer.

Explanation

In composite fish culture the rearing sequence runs from spawn to fry, then fingerling, then grow-out, and each stage is held in a pond of a particular size. The small, shallow pond that receives spawn and produces fry is the nursery pond. Fry are then transferred to a rearing pond and later to stocking ponds.

Question 43Pond Construction, Soil and Water Quality Management: site selection, pond types, liming, fertilization, dissolved oxygen, pH, ammonia

Liming an acidic pond bottom and water primarily aims to

  1. increase the toxicity of un-ionized ammonia
  2. supply nitrogen and phosphorus to the phytoplankton
  3. increase the oxygen demand of the bottom mud
  4. raise pH and total alkalinity Correct answer.

Explanation

Lime neutralises acidity in the bottom soil and the water, raising pH and increasing total alkalinity, which buffers the daily pH swing. Higher alkalinity also improves the availability of phosphorus to phytoplankton. Reduced disease pressure in the mud is a useful secondary benefit.

Question 44Pond Construction, Soil and Water Quality Management: site selection, pond types, liming, fertilization, dissolved oxygen, pH, ammonia

For good feeding and growth in a managed carp pond, dissolved oxygen should preferably be maintained above

  1. 1 mg per litre
  2. 3 mg per litre
  3. 2 mg per litre
  4. 5 mg per litre Correct answer.

Explanation

Carp feed actively and grow well when dissolved oxygen stays above about 5 mg per litre. Below 3 mg/L, feeding declines and fish crowd at the surface. Values near 1 to 2 mg/L can cause mortality, especially at dawn or after cloudy weather.

Question 45Pond Construction, Soil and Water Quality Management: site selection, pond types, liming, fertilization, dissolved oxygen, pH, ammonia

At a fixed total ammonia concentration in pond water, the proportion present as toxic un-ionized ammonia rises when

  1. pH and temperature decrease
  2. pH and temperature increase Correct answer.
  3. pH increases and temperature falls
  4. pH falls and temperature rises

Explanation

Total ammonia exists as ammonium ion and un-ionized ammonia in an equilibrium that depends on pH and temperature. As pH rises, more ammonium ion loses a proton and becomes NH3. Higher temperature also favours the un-ionized, toxic form.

Question 46Pond Construction, Soil and Water Quality Management: site selection, pond types, liming, fertilization, dissolved oxygen, pH, ammonia

Using a Secchi disc, a pond is judged to have an adequate plankton bloom for carp culture when the disc disappears at a depth of about

  1. 30-40 cm Correct answer.
  2. 60-80 cm
  3. 100-120 cm
  4. 10-15 cm

Explanation

Secchi disc transparency is a practical field index of plankton density. A reading of roughly 30-40 cm indicates a healthy bloom that shades the bottom and supports fish food organisms. Much shorter readings suggest over-fertilization, with a risk of nocturnal oxygen depletion.

Question 47Pond Construction, Soil and Water Quality Management: site selection, pond types, liming, fertilization, dissolved oxygen, pH, ammonia

For a tropical grow-out carp pond, the recommended water depth at the deepest point is about

  1. 0.8-1.0 m
  2. 0.3-0.5 m
  3. 5-7 m
  4. 1.5-2.5 m Correct answer.

Explanation

A grow-out carp pond in the tropics is normally built with 1.5-2.5 m of water at the deepest point. This depth moderates temperature swings, gives fish a refuge from surface heat or cold, and still allows light to reach the bottom for plankton production. Shallow ponds overheat, while very deep ponds develop anoxic bottom layers.

Question 48Pond Construction, Soil and Water Quality Management: site selection, pond types, liming, fertilization, dissolved oxygen, pH, ammonia

The most suitable water pH range for carp culture is

  1. 9.0-10.0
  2. 6.5-8.5 Correct answer.
  3. 5.5-6.5
  4. 4.5-5.5

Explanation

Carp culture performs best in water of pH 6.5 to 8.5, where nutrients remain available and ammonia toxicity stays limited. Values below 6.5 reduce growth, reproduction and plankton production. Values above 9 shift a larger share of ammonia into the toxic un-ionized form.

Question 49Pond Construction, Soil and Water Quality Management: site selection, pond types, liming, fertilization, dissolved oxygen, pH, ammonia

In a pond carrying a dense phytoplankton bloom, the concentration of toxic un-ionized ammonia is usually highest in the late afternoon because

  1. phytoplankton absorb ammonium and release ammonia at sunset
  2. respiration adds carbon dioxide and raises the pH of the water
  3. photosynthesis raises pH, favouring NH3 Correct answer.
  4. ammonia is excreted by fish only during daylight hours

Explanation

In the afternoon, intense photosynthesis by dense phytoplankton removes carbon dioxide from the water, and the loss of CO2 raises pH. A higher pH shifts the ammonium-ammonia equilibrium towards un-ionized NH3. Thus the toxic fraction peaks late in the day even when total ammonia is unchanged.

Question 50Pond Construction, Soil and Water Quality Management: site selection, pond types, liming, fertilization, dissolved oxygen, pH, ammonia

A pond soil has pH 5.0 and the water shows total alkalinity of only 20 mg per litre as CaCO3. The most appropriate management action before stocking is to

  1. add fresh cow dung at 5,000 kg per hectare
  2. apply agricultural limestone and re-test before stocking Correct answer.
  3. flush the pond with saline water
  4. apply urea to stimulate a phytoplankton bloom

Explanation

A soil pH of 5.0 together with water alkalinity of only 20 mg/L as CaCO3 indicates a strongly acidic, poorly buffered pond. Agricultural limestone raises soil pH and total alkalinity, and the dose should be checked by re-testing before fish are stocked. Fertilizers should be applied only after the lime requirement is corrected.