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Maharashtra HSC Fresh Water Fish Culture (C1) study materials
Maharashtra HSC Fresh Water Fish Culture (C1) study resources

Maharashtra HSC Fresh Water Fish Culture (C1) practice questions

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Question 1Introduction to Freshwater Aquaculture and Fisheries Resources

In freshwater aquaculture terminology, which group of organisms is referred to as 'plankton' that serves as natural food for fish fry in a pond?

  1. Phytoplankton and zooplankton drifting in the water column Correct answer.
  2. Macrophytes rooted in the pond soil
  3. Predatory insects flying above the pond surface
  4. Benthic snails and mussels attached to the pond bottom

Explanation

Plankton means the free-floating or weakly swimming microscopic organisms, comprising phytoplankton (algae) and zooplankton (rotifers, cladocerans, copepods). They form the base of the pond food chain and are the first natural food of fish fry. Benthic molluscs, rooted macrophytes and aerial insects are not plankton.

Question 2Introduction to Freshwater Aquaculture and Fisheries Resources

Which of the following is classified as an exotic (introduced) freshwater fish species in India?

  1. Catla catla
  2. Oreochromis niloticus Correct answer.
  3. Cirrhinus mrigala
  4. Labeo rohita

Explanation

Oreochromis niloticus, the Nile tilapia, was introduced to India from Africa and is therefore an exotic species. Catla, mrigal and rohu are the Indian major carps, native to the Indian subcontinent. Recognizing exotic status matters because introduced species can compete with native carp stocks.

Question 3Introduction to Freshwater Aquaculture and Fisheries Resources

A farmer wants to stock a pond with the three Indian major carps in a polyculture system. Which combination correctly names them?

  1. Catla, rohu and mrigal Correct answer.
  2. Catla, silver carp and tilapia
  3. Rohu, common carp and grass carp
  4. Mrigal, milkfish and mullet

Explanation

The Indian major carps are catla (Catla catla), rohu (Labeo rohita) and mrigal (Cirrhinus mrigala). They are the traditional species of composite carp culture in India because they occupy different feeding niches. Common carp, silver carp, grass carp and tilapia are exotic or non-major species.

Question 4Introduction to Freshwater Aquaculture and Fisheries Resources

Which term describes the practice of rearing fish in ponds where the water is largely stagnant and managed mainly by fertilization and supplementary feeding?

  1. Cage culture in a reservoir
  2. Static pond culture Correct answer.
  3. Raceway culture
  4. Pen culture in a wetland

Explanation

Static pond culture is the traditional freshwater system in which water is not continuously flowing and production depends on natural food generated by fertilization plus supplementary feed. Raceway, cage and pen systems depend on flowing or exchanged water and enclosed structures. The distinction is fundamental to freshwater aquaculture classification.

Question 5Introduction to Freshwater Aquaculture and Fisheries Resources

In fish culture, the term 'stocking density' refers to which quantity?

  1. Percentage of dissolved oxygen present in the pond
  2. Weight of supplementary feed given per day
  3. Depth of water maintained in the pond
  4. Number of fish introduced per unit area or volume of water Correct answer.

Explanation

Stocking density expresses how many fish are released into a pond per unit area (for example per square metre or hectare) or per unit volume. It is distinct from feeding rate, water depth and water quality parameters. Correct density calculation is essential for planning seed requirements and avoiding overcrowding.

Question 6Introduction to Freshwater Aquaculture and Fisheries Resources

Which freshwater fish is commonly described as a 'weed fish' that competes with cultured carp for food in nursery ponds?

  1. Gambusia affinis Correct answer.
  2. Cirrhinus mrigala
  3. Catla catla
  4. Labeo rohita

Explanation

Gambusia affinis, the mosquito fish, is a small prolific species often regarded as a weed or unwanted fish in carp nursery ponds because it multiplies rapidly and competes for food and space. Rohu, catla and mrigal are the desired cultured major carps. Weed fish control is part of pond preparation.

Question 7Introduction to Freshwater Aquaculture and Fisheries Resources

A pond manager observes that the water has turned deep green with dense algal growth and the morning dissolved oxygen is very low. Which explanation best fits this situation?

  1. Excess supplementary feed has raised oxygen levels directly
  2. High water transparency indicates a collapse of the food chain
  3. Heavy phytoplankton bloom causes night-time oxygen depletion through respiration Correct answer.
  4. Low alkalinity prevents any algal growth in the pond

Explanation

A dense phytoplankton bloom produces oxygen by day but consumes large amounts of oxygen at night through respiration, so pre-dawn oxygen can fall sharply. This is a classic cause of early-morning oxygen depletion and fish distress. Low alkalinity and high transparency would not explain dense green water.

Question 8Introduction to Freshwater Aquaculture and Fisheries Resources

In composite fish culture, catla, rohu and mrigal are stocked together mainly because they occupy different feeding niches. Which pairing of species with its feeding zone is correct?

  1. Catla as a bottom feeder, rohu as a surface feeder and mrigal as a column feeder
  2. Catla as a bottom feeder, rohu as a column feeder and mrigal as a surface feeder
  3. Catla as a surface feeder, rohu as a column feeder and mrigal as a bottom feeder Correct answer.
  4. Catla as a column feeder, rohu as a bottom feeder and mrigal as a surface feeder

Explanation

Catla has an upturned mouth and feeds in the upper water layer, rohu feeds in the middle column, and mrigal with its inferior mouth grubs on the bottom. This spatial separation reduces competition and allows higher total yield per pond. It is the ecological basis of composite carp culture.

Question 9Introduction to Freshwater Aquaculture and Fisheries Resources

A farmer calculates that a 1-hectare pond stocked at 5,000 fingerlings per hectare will give a survival of 80 percent. Approximately how many fish will be harvested?

  1. 1,000
  2. 800
  3. 4,000 Correct answer.
  4. 5,000

Explanation

Expected harvest equals stocking number multiplied by survival rate, so 5,000 multiplied by 0.80 gives 4,000 fish. This calculation is used to estimate final yield and marketable biomass. Stocking number itself, or the mortality figure, must not be mistaken for the harvest count.

Question 10Introduction to Freshwater Aquaculture and Fisheries Resources

Which pond preparation step is most important for eliminating unwanted predatory and weed fish before stocking carp seed?

  1. Introducing floating macrophytes for shade
  2. Drying and applying lime or a suitable fish toxicant such as mahua oil cake Correct answer.
  3. Adding urea and single super phosphate to boost plankton
  4. Increasing water depth by pumping in canal water

Explanation

Pond preparation for eradication of predators and weed fish involves sun-drying the bottom and applying lime or a recommended fish toxicant such as mahua oil cake before stocking. Fertilization and water addition come after eradication, not instead of it. Introducing macrophytes would shelter unwanted fish rather than remove them.

Question 11Introduction to Freshwater Aquaculture and Fisheries Resources

Which freshwater fish species is a herbivore commonly stocked to control excessive aquatic macrophytes in a pond?

  1. Clarias batrachus
  2. Mrigal (Cirrhinus mrigala)
  3. Grass carp (Ctenopharyngodon idella) Correct answer.
  4. Silver carp (Hypophthalmichthys molitrix)

Explanation

Grass carp is a herbivorous exotic carp that consumes aquatic weeds and is stocked for weed control as well as production. Silver carp is a filter feeder on phytoplankton, mrigal is a bottom detritus feeder, and Clarias is an air-breathing catfish. Matching species to feeding habit is central to aquaculture planning.

Question 12Introduction to Freshwater Aquaculture and Fisheries Resources

A nursery pond manager wants to produce zooplankton-rich water quickly for newly hatched carp spawn. Which management action is most appropriate?

  1. Lowering water temperature by adding cold well water
  2. Applying well-rotted organic manure to encourage zooplankton Correct answer.
  3. Applying copper sulphate to sterilize the pond water
  4. Removing all phytoplankton to leave clear water

Explanation

Organic manure supplies bacteria and nutrients that stimulate the microbial and algal food chain, promoting zooplankton such as rotifers and cladocerans needed by spawn. Copper sulphate is algicidal and would reduce food organisms. Cooling water and clearing algae would reduce rather than increase natural food.

Question 13Introduction to Freshwater Aquaculture and Fisheries Resources

Which of the following best describes 'composite fish culture' as practised in Indian freshwater ponds?

  1. Rearing several compatible carp species with different feeding habits together in one pond Correct answer.
  2. Rearing a single species at very high density in a recirculating system
  3. Rearing fish together with prawns in brackishwater ponds
  4. Rearing fish in floating cages within a large reservoir

Explanation

Composite fish culture combines several carp species with complementary feeding niches in the same pond so that food available at all levels is used efficiently. It is not a single-species intensive system, nor a brackishwater polyculture, nor a cage system. The ecological complementarity raises total production per unit area.

Question 14Introduction to Freshwater Aquaculture and Fisheries Resources

Which water quality parameter is most directly managed by applying agricultural lime to a freshwater fish pond?

  1. Water temperature
  2. Total alkalinity and pH Correct answer.
  3. Ammonia toxicity directly
  4. Dissolved oxygen concentration

Explanation

Lime raises total alkalinity and pH and buffers the pond against wide pH swings, which in turn supports stable plankton production. It does not directly control temperature or dissolve oxygen. Ammonia toxicity may be indirectly influenced but is not the primary target of liming.

Question 15Introduction to Freshwater Aquaculture and Fisheries Resources

A hatchery technician needs to induce breeding in an Indian major carp outside the natural spawning season. Which technique is standard?

  1. Exposure of brood fish to strong light for 24 hours
  2. Starvation of brood fish for one week
  3. Transfer of brood fish to saline water
  4. Injection of pituitary gland extract or a synthetic hormone such as ovaprim Correct answer.

Explanation

Induced breeding in carps is done by injecting pituitary gland extract or synthetic hormones such as ovaprim or human chorionic gonadotropin to trigger ovulation and spawning. Light exposure, saline transfer and starvation are not spawning induction methods. This technique allows seed production when natural spawning does not occur.

Question 16Introduction to Freshwater Aquaculture and Fisheries Resources

A farmer's pond shows abundant plankton but fish growth is poor and the water has a musty odour with decaying bottom sludge. Which management measure is most appropriate?

  1. Reduce excessive feeding and remove or oxidize the bottom sludge Correct answer.
  2. Increase feeding rate to compensate for slow growth
  3. Add more organic manure to boost plankton further
  4. Stop all water exchange permanently

Explanation

Accumulated uneaten feed and organic sludge decompose and consume oxygen, producing off-flavours and stressing fish even when plankton looks abundant. Reducing feed and removing or oxidizing sludge restores bottom condition. Adding more feed or manure would worsen the oxygen demand of the pond.

Question 17Introduction to Freshwater Aquaculture and Fisheries Resources

In a polyculture pond, silver carp and catla both feed on plankton, while grass carp eats macrophytes. A manager wants to maximize use of the phytoplankton crop without excessive competition. Which reasoning is most sound?

  1. Silver carp should be stocked at a moderate proportion because it competes with catla for plankton Correct answer.
  2. Grass carp should be stocked heavily because it eats phytoplankton
  3. No plankton feeder should be stocked if catla is present
  4. Silver carp should replace all catla because filter feeders always yield more

Explanation

Silver carp and catla overlap in feeding on plankton, so over-stocking silver carp would intensify competition and depress catla growth. A moderate proportion of silver carp uses the finer phytoplankton fraction while leaving room for catla. Grass carp does not eat phytoplankton, and excluding all plankton feeders wastes the food resource.

Question 18Introduction to Freshwater Aquaculture and Fisheries Resources

A 0.5-hectare pond is stocked with 3,000 rohu fingerlings and 2,000 catla fingerlings. What is the combined stocking density per hectare?

  1. 5,000 per hectare
  2. 10,000 per hectare Correct answer.
  3. 2,500 per hectare
  4. 6,000 per hectare

Explanation

Total fingerlings stocked are 3,000 plus 2,000, equal to 5,000, in a 0.5-hectare pond. Dividing 5,000 by 0.5 gives 10,000 fingerlings per hectare. Reporting the raw total or dividing by the wrong area gives misleading density figures.

Question 19Introduction to Freshwater Aquaculture and Fisheries Resources

A farmer plans to introduce Nile tilapia into an existing carp pond. Which consideration is most important from a resource-management viewpoint?

  1. Tilapia cannot survive in freshwater ponds at all
  2. Tilapia is a strict carnivore that will eliminate all plankton
  3. Tilapia breeds prolifically and may overpopulate and compete with carp, so controlled all-male stocking is preferred Correct answer.
  4. Tilapia is a slow breeder and will not affect carp populations

Explanation

Nile tilapia matures early and breeds repeatedly in ponds, producing stunted populations that compete with carp for food and space. All-male or monosex stocking is a common management response. Tilapia is an omnivorous filterer that thrives in freshwater, so the other statements are incorrect.

Question 20Introduction to Freshwater Aquaculture and Fisheries Resources

Why is regular sampling of fish growth in a nursery pond considered essential management practice?

  1. It replaces the need for any water quality monitoring
  2. It allows adjustment of feeding and stocking before stunting and size variation become severe Correct answer.
  3. It guarantees that no fish will die during the culture period
  4. It is required only to calculate the market price of the final harvest

Explanation

Growth sampling reveals whether fish are growing at the expected rate and whether size variation or stunting is developing, allowing timely adjustment of feed, density or grading. It does not replace water quality checks or guarantee survival. Market pricing is not the purpose of growth sampling.

Question 21Fish Biology, Anatomy and Identification of Cultivable Species

In the body of a typical culturable freshwater teleost such as Catla catla, the swim bladder lies immediately ventral to which structure?

  1. The kidney
  2. The liver
  3. The vertebral column Correct answer.
  4. The intestine

Explanation

In most freshwater teleosts the swim bladder is a gas-filled sac lying in the dorsal coelom just below the vertebral column and above the gut. This dorsal position lets it act as a hydrostatic organ without displacing the heavier visceral mass. The kidney in carps is retroperitoneal and more closely applied to the vertebral column itself.

Question 22Fish Biology, Anatomy and Identification of Cultivable Species

Which scale type, with its exposed portion bearing fine ridges (circuli) and its buried portion marked by radii, is characteristic of Indian major carps?

  1. Cycloid scale Correct answer.
  2. Ganoid scale
  3. Placoid scale
  4. Ctenoid scale

Explanation

Cycloid scales are thin, rounded, overlapping scales with concentric circuli and no spines on the posterior margin; they are typical of carps and other soft-rayed fishes. Placoid scales occur in sharks and rays, ganoid scales in gars, and ctenoid scales in spiny-rayed fishes. Annuli on cycloid scales are also used in age determination.

Question 23Fish Biology, Anatomy and Identification of Cultivable Species

A culturist wants to confirm the identity of Labeo rohita among harvested carps. Which feature combination best supports this identification?

  1. Superior mouth with a long dorsal fin and no barbels
  2. Small upward mouth with a scaleless head and no lateral line
  3. Terminal mouth with a pointed snout and no barbels
  4. Inferior mouth with a pair of barbels and a reddish tinge on the fins Correct answer.

Explanation

Rohu is recognised by a somewhat inferior mouth, a pair of short barbels, a fairly deep body and often a reddish tinge on the pectoral, pelvic and anal fins. The inferior mouth suits bottom and mid-water grazing. Catla, by contrast, has an upturned mouth and no barbels, which is a useful field separation.

Question 24Fish Biology, Anatomy and Identification of Cultivable Species

In a fish, the structure that connects the swim bladder to the gut and allows gas to be added or removed is called the:

  1. Pneumatic duct Correct answer.
  2. Spiral valve
  3. Branchiostegal ray
  4. Nephrostome

Explanation

The pneumatic duct is the tube linking the swim bladder to the oesophagus or gut, allowing gas to be released or taken in. Fishes with this duct are called physostomous, a condition found in carps. In physoclistous fishes the duct is absent in the adult and gas is handled by the gas gland and rete mirabile.

Question 25Fish Biology, Anatomy and Identification of Cultivable Species

A pond manager notices a carp holding position near the surface with its mouth frequently breaking the water and gulping air. Which anatomical feature most directly explains this behaviour?

  1. A reduced gill surface area
  2. A well-developed accessory respiratory organ Correct answer.
  3. An open connection between the opercular cavity and the gut
  4. A physostomous swim bladder with a pneumatic duct

Explanation

Several culturable fishes such as Clarias, Heteropneustes and Anabas possess accessory respiratory organs that let them use atmospheric air, and they habitually come to the surface to gulp it. Their tolerance of low dissolved oxygen in stagnant ponds follows directly from this anatomy. In carps, by contrast, the physostomous bladder is not an air-breathing organ.

Question 26Fish Biology, Anatomy and Identification of Cultivable Species

The gill filaments of a freshwater teleost are supported by which skeletal element?

  1. Maxillary and premaxillary bones
  2. Cleithrum and coracoid bones
  3. Ceratobranchial and epibranchial bones Correct answer.
  4. Basihyal and glossohyal bones

Explanation

The gill arch is built of paired bones including the ceratobranchial and epibranchial, which carry the filaments and their secondary lamellae. These arch elements are part of the branchial skeleton. Maxillary and premaxillary bones belong to the jaws, and cleithrum and coracoid to the pectoral girdle.

Question 27Fish Biology, Anatomy and Identification of Cultivable Species

Which of the following culturable species is best described as an air-breathing catfish with a long, scaleless body and a single long dorsal fin running almost to the tail?

  1. Cirrhinus mrigala
  2. Clarias batrachus Correct answer.
  3. Oreochromis mossambicus
  4. Cyprinus carpio

Explanation

Clarias batrachus, the walking catfish, has an elongated scaleless body and a long-based dorsal fin without a spine, and it can breathe air through a dendritic accessory organ. This makes it suited to shallow, oxygen-poor waters. Mrigal, common carp and tilapia all have scaly bodies and different fin arrangements.

Question 28Fish Biology, Anatomy and Identification of Cultivable Species

In a cross-section of a fish's body, the lateral line canal runs along the flank. Its primary function is to:

  1. Detect pressure waves and water movements Correct answer.
  2. Carry oxygenated blood to the skin
  3. Provide attachment for the myotomes
  4. Secret mucus for body lubrication

Explanation

The lateral line is a mechanosensory system of neuromasts in a canal that detects water currents, pressure waves and low-frequency vibrations. It helps schooling, prey detection and predator avoidance. Mucus production, blood supply and muscle attachment are separate functions of other tissues.

Question 29Fish Biology, Anatomy and Identification of Cultivable Species

A candidate examines a preserved specimen and finds a stout serrated spine at the front of the dorsal fin, a pair of long barbels at the corners of the mouth and a scaly body. Which species is most likely?

  1. Labeo catla
  2. Cyprinus carpio Correct answer.
  3. Heteropneustes fossilis
  4. Channa punctatus

Explanation

Common carp, Cyprinus carpio, has a stout serrated spine as the first dorsal-fin ray and two pairs of barbels, one short and one long. The serrated spine is a reliable distinguishing character in the field. Heteropneustes lacks the spiny dorsal fin, catla lacks barbels, and Channa has a long dorsal fin without a serrated spine.

Question 30Fish Biology, Anatomy and Identification of Cultivable Species

Which structure in the fish heart receives deoxygenated blood returning from the body before it enters the atrium?

  1. Ventricle
  2. Bulbus arteriosus
  3. Sinus venosus Correct answer.
  4. Conus arteriosus

Explanation

In the fish heart, blood returns via the sinus venosus, which feeds the atrium, then the ventricle, and leaves through the bulbus or conus arteriosus. The sinus venosus is a thin-walled collecting chamber and acts as the pacemaker region in many fishes. The ventricle is the muscular pump downstream of the atrium.

Question 31Fish Biology, Anatomy and Identification of Cultivable Species

In the digestive tract of a carp, the pharyngeal teeth are located in the:

  1. Lower jaw
  2. Upper jaw
  3. Pharyngeal region behind the gills Correct answer.
  4. Oesophagus

Explanation

Carps have no oral teeth; instead they bear pharyngeal teeth on the lower pharyngeal bones in the throat region behind the gill arches. These teeth grind food against a horny pad on the base of the skull. The shape and number of pharyngeal teeth are also used in species identification.

Question 32Fish Biology, Anatomy and Identification of Cultivable Species

A pond owner reports that stocked grass carp are eating only soft aquatic vegetation and ignoring coarser plants. Which anatomical feature most directly relates to this feeding habit?

  1. Pharyngeal teeth with comb-like serrations for shredding plant matter Correct answer.
  2. A stomach with a thick muscular gizzard
  3. A short oesophagus with no pharyngeal teeth
  4. A very long intestine suited only to plankton

Explanation

Grass carp possess comb-like, serrated pharyngeal teeth that shred coarse plant material before it passes to the gut. Their long coiled intestine then handles the bulky, low-quality diet. This anatomy explains why they are effective for macrophyte control in ponds.

Question 33Fish Biology, Anatomy and Identification of Cultivable Species

Which fin formula feature helps distinguish a fish with a spiny dorsal fin from one with only soft rays?

  1. Presence of a lateral line
  2. Number of caudal fin lobes
  3. Number of pelvic fin rays
  4. Presence of unbranched, stiff rays in the anterior dorsal fin Correct answer.

Explanation

Spiny-rayed fishes have stiff, unbranched, pointed rays at the front of the dorsal fin, while soft-rayed fishes have segmented, branched and flexible rays. Fin formulae record this as, for example, D XI, 12 versus D 15. The caudal lobes, lateral line and pelvic ray count do not separate these conditions.

Question 34Fish Biology, Anatomy and Identification of Cultivable Species

The operculum of a teleost fish is formed mainly by which set of bones?

  1. Frontal, parietal and supraoccipital
  2. Cleithrum, scapula and coracoid
  3. Opercle, preopercle, interoperculum and subopercle Correct answer.
  4. Maxilla, premaxilla and dentary

Explanation

The gill cover of a teleost is a series of dermal bones: opercle, preopercle, interoperculum and subopercle. These protect the gills and help pump water across them during respiration. The frontal and parietal bones belong to the skull roof, and the maxilla and premaxilla to the jaws.

Question 35Fish Biology, Anatomy and Identification of Cultivable Species

In an Indian major carp polyculture pond, a fish with a deep body, a very large head and an upturned mouth is caught. Which species is it?

  1. Labeo bata
  2. Labeo rohita
  3. Cirrhinus mrigala
  4. Labeo catla Correct answer.

Explanation

Labeo catla (catla) is identified by its deep body, very large head and short upturned mouth with a projecting lower jaw, and it lacks barbels. This surface-feeding habit is why it occupies the upper zone in composite culture. Rohu has an inferior mouth with barbels, and mrigal has a more slender body.

Question 36Fish Biology, Anatomy and Identification of Cultivable Species

The air-breathing organ of Heteropneustes fossilis is best described as:

  1. A modified swim bladder only
  2. A pair of tubular, posteriorly extended respiratory sacs Correct answer.
  3. A labyrinthine chamber in the head
  4. A set of arborescent gill trees above the gills

Explanation

Heteropneustes fossilis, the stinging catfish, has a pair of long tubular air sacs extending backwards from the gill chamber, which function as accessory respiratory organs. Anabas has a labyrinth, Clarias has arborescent dendritic organs, and many other fishes use a modified swim bladder. Knowing these differences helps match species to oxygen-poor ponds.

Question 37Fish Biology, Anatomy and Identification of Cultivable Species

A fish is found to have a heterocercal tail in which the upper lobe is larger and contains the upturned vertebral column. This tail type is most typical of:

  1. Tilapia
  2. Channa species
  3. Sharks and other elasmobranchs Correct answer.
  4. Indian major carps

Explanation

A heterocercal tail has unequal lobes with the vertebral column extending into the larger upper lobe, as in sharks and other elasmobranchs. Most culturable freshwater teleosts, including carps, tilapia and Channa, have a homocercal tail with externally symmetrical lobes. Tail form is a useful identification character at the higher taxonomic level.

Question 38Fish Biology, Anatomy and Identification of Cultivable Species

In the classification of cultivable fishes, which feature is used to place catfishes separately from carps in field identification keys?

  1. Absence of scales and presence of a stout leading dorsal spine in many forms Correct answer.
  2. Presence of a lateral line
  3. Presence of barbels around the mouth
  4. Presence of paired pectoral fins

Explanation

Catfishes typically have scaleless skin, and many culturable forms have a stout dorsal spine, which separates them from scaled carps in identification keys. Barbels occur in both groups, so they do not separate them. The lateral line and paired pectoral fins are common to both.

Question 39Fish Biology, Anatomy and Identification of Cultivable Species

The number of gill arches bearing filaments on each side of a typical teleost is:

  1. Three
  2. Four Correct answer.
  3. Six
  4. Five

Explanation

A typical teleost has four functional gill arches on each side, each bearing two rows of filaments. A fifth arch is usually reduced and lacks filaments, forming the lower pharyngeal skeleton. The total gill surface is therefore organised over eight arches, four per side.

Question 40Fish Biology, Anatomy and Identification of Cultivable Species

A hatchery technician needs to sex mature Cyprinus carpio brooders before induced breeding. Which external feature is most reliable?

  1. Males are always larger and deeper-bodied than females
  2. Males have a distinct genital papilla and a softer belly
  3. Females have a longer dorsal fin base than males
  4. Females have a rounded, distended abdomen and males show pearl organs on the head and pectoral fins Correct answer.

Explanation

In mature common carp, females have a fuller, rounded abdomen swollen with eggs, while males develop rough pearl organs on the head and pectoral fin rays during the breeding season. The genital papilla is more useful in tilapia and catfish. Size and dorsal fin base are not reliable sex characters in carp.

Question 41Fish Biology, Anatomy and Identification of Cultivable Species

Which statement correctly describes the position of the pectoral fins in a typical carp?

  1. They are paired fins just behind the operculum on the sides Correct answer.
  2. They are paired fins on the ventral surface behind the pelvic fins
  3. They are median fins just before the tail
  4. They are median fins on the mid-dorsal line

Explanation

Pectoral fins are paired appendages placed on the sides just behind the operculum and are supported by the pectoral girdle. They help in steering, braking and slow swimming. Pelvic fins are also paired but lie further back on the ventral surface, while dorsal, anal and caudal fins are median and unpaired.

Question 42Fish Biology, Anatomy and Identification of Cultivable Species

During examination of a fish gut, a technician finds a long coiled intestine with several loops and no distinct stomach. This anatomy is most consistent with which feeding type?

  1. Purely carnivorous feeding
  2. Planktonic filter feeding only
  3. Detritus feeding with a gizzard
  4. Herbivorous or omnivorous feeding Correct answer.

Explanation

Herbivorous and omnivorous fishes such as carps have a long, coiled intestine to increase digestion and absorption time for bulky plant food, and many lack a distinct stomach. Carnivores typically have a short, straight gut and a well-defined stomach. Filter feeders and detritus feeders have other specialised features.

Question 43Fish Biology, Anatomy and Identification of Cultivable Species

The characteristic dark spot at the base of the caudal fin, together with a long dorsal fin and a scaleless head, is used to identify which culturable species?

  1. Channa punctatus Correct answer.
  2. Labeo catla
  3. Clarias batrachus
  4. Cirrhinus mrigala

Explanation

Channa punctatus, the spotted snakehead, has an elongated body, a long dorsal fin of soft rays, a scaleless head and a dark blotch or spot near the caudal base. These features fit the snakehead body plan. Catla, mrigal and Clarias differ in body shape and in the presence of scales or barbels.

Question 44Fish Biology, Anatomy and Identification of Cultivable Species

Which of the following correctly pairs a culturable fish with its typical feeding zone in a composite pond?

  1. Mrigal with the surface zone
  2. Rohu with the middle zone Correct answer.
  3. Catla with the bottom zone
  4. Grass carp with the surface plankton zone

Explanation

In Indian major carp polyculture, catla feeds near the surface, rohu in the middle column and mrigal near the bottom. This partitioning reduces competition for food among the stocked species. Grass carp is primarily a macrophyte feeder rather than a surface plankton feeder.

Question 45Pond Construction, Soil and Water Quality Management

In freshwater fish pond construction, which soil characteristic is most desirable for the pond bottom to hold water effectively?

  1. A high proportion of gravel mixed with pebbles
  2. A high proportion of clay with adequate compaction Correct answer.
  3. A high proportion of coarse sand with loose structure
  4. A high proportion of organic muck with plant debris

Explanation

Clay-rich soil swells when wet and, when properly compacted, forms a dense layer with very low permeability that limits seepage. Sandy, gravelly, or highly organic bottoms have large pore spaces or decaying matter and allow water to drain away or destabilise the bottom.

Question 46Pond Construction, Soil and Water Quality Management

A pond dyke is being built on a site where the subsoil is highly permeable sand. Which construction measure best reduces seepage through the dyke base?

  1. Extending a clay core trench down into an impervious layer Correct answer.
  2. Increasing the height of the dyke above the water line
  3. Adding a gravel apron along the inner face of the dyke
  4. Widening the top width of the dyke for vehicle access

Explanation

A clay core trench carried down to an impervious stratum cuts off the permeable path beneath the dyke, which is the usual seepage route on sandy sites. Height, top width, and surface aprons affect stability or access but do not block subsurface flow.

Question 47Pond Construction, Soil and Water Quality Management

Which pond type is designed so that water can be drained completely by gravity for harvesting and bottom drying?

  1. A pond constructed at a level below the drainage channel
  2. A pond fed only by seepage with a raised embankment
  3. A pond with a properly sloped bottom and a monk or sluice outlet Correct answer.
  4. A pond with a flat bottom and no outlet structure

Explanation

Complete gravity drainage requires the bottom to slope towards an outlet whose sill is at the lowest point and whose discharge level is above the drainage channel. A flat bottom without an outlet, or a pond sited below the outlet channel, cannot be emptied by gravity.

Question 48Pond Construction, Soil and Water Quality Management

In a brackish or saline groundwater area, which pond management practice is most appropriate to limit salt accumulation in the pond bottom?

  1. Applying lime heavily at every water addition
  2. Adding organic manure to the bottom before filling
  3. Periodic flushing and avoiding excessive evaporation without replenishment Correct answer.
  4. Keeping the pond permanently full without any exchange

Explanation

Salts accumulate in the soil and water when evaporation concentrates them, so periodic flushing with good-quality water and maintaining adequate depth reduce accumulation. Heavy liming, permanent stagnation, or raw manure application does not remove salts and may worsen water quality.

Question 49Pond Construction, Soil and Water Quality Management

Which water quality parameter is most directly measured with a Secchi disc in a fish pond?

  1. Water transparency as an index of plankton density Correct answer.
  2. Total alkalinity expressed as calcium carbonate
  3. Dissolved oxygen concentration in milligrams per litre
  4. Free ammonia concentration in the water

Explanation

A Secchi disc measures the depth at which it disappears from view, giving a simple index of turbidity and plankton abundance. Dissolved oxygen, alkalinity, and ammonia require chemical or electronic measurement, not a visibility disc.

Question 50Pond Construction, Soil and Water Quality Management

Pond water shows a total alkalinity of about 15 mg/L as CaCO3. Which treatment is most appropriate to raise alkalinity and stabilise pH?

  1. Increasing the stocking density of carp
  2. Adding urea to stimulate phytoplankton growth
  3. Applying agricultural lime at a rate based on soil and water testing Correct answer.
  4. Applying common salt to the pond water

Explanation

Low alkalinity reduces the buffering capacity, so liming with agricultural lime raises alkalinity and stabilises pH swings. Urea, higher stocking, and common salt do not increase carbonate buffering and may stress fish.