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Fisheries Technologist practice questions

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Question 1Fisheries Technology (domain weights not published in source)

In a closed, static fish pond, the amount of dissolved oxygen that can remain in solution at a given temperature is best described by which term?

  1. Biochemical oxygen demand
  2. Apparent digestibility
  3. Osmotic pressure
  4. Saturation concentration Correct answer.

Explanation

Saturation concentration is the maximum dissolved oxygen a water body can hold at a given temperature and salinity under equilibrium with the atmosphere. BOD measures oxygen consumed by decomposition, not the holding capacity, and digestibility and osmotic pressure belong to nutrition and physiology.

Question 2Fisheries Technology (domain weights not published in source)

A hatchery manager needs to determine the sex of mature Nile tilapia before stocking a breeding pond. Which external feature reliably distinguishes males?

  1. Two separate openings visible on the ventral surface
  2. A rounded, swollen abdomen with a reddish vent
  3. A long anal fin extending beyond the caudal peduncle
  4. A single urogenital papilla with a distinct genital tassel Correct answer.

Explanation

Mature male tilapia show a single urogenital papilla and, in many strains, a genital tassel, whereas females have separate genital and anal openings. Abdomen shape and fin length are not dependable sex indicators in tilapia.

Question 3Fisheries Technology (domain weights not published in source)

Which statement describes the correct use of a Secchi disk in pond management?

  1. It measures the total dissolved solids by weighing the residue left after evaporation.
  2. It estimates water transparency by the depth at which the disk disappears from view. Correct answer.
  3. It quantifies ammonia concentration through a colorimetric reaction.
  4. It records the dissolved oxygen profile at one-metre intervals.

Explanation

The Secchi disk is lowered until it is no longer visible, and that depth is recorded as a transparency index used to judge plankton density and pond fertility. It does not measure dissolved solids, ammonia, or oxygen directly.

Question 4Fisheries Technology (domain weights not published in source)

A pond has a total alkalinity of 15 mg/L as CaCO3 and a morning pH of 6.2. Which management action is most appropriate?

  1. Apply copper sulfate to control algae.
  2. Increase feeding rate to stimulate phytoplankton.
  3. Add ammonium sulfate to increase nitrogen availability.
  4. Apply agricultural limestone to raise alkalinity and buffer pH. Correct answer.

Explanation

Low alkalinity leaves the pond poorly buffered, so pH swings widely and liming with agricultural limestone raises alkalinity and stabilizes pH. Adding acidifying fertilizer, more feed, or an algicide would worsen the imbalance.

Question 5Fisheries Technology (domain weights not published in source)

In a recirculating aquaculture system, which component is primarily responsible for converting ammonia to nitrate?

  1. The ultraviolet sterilizer
  2. The biofilter carrying nitrifying bacteria Correct answer.
  3. The foam fractionator
  4. The mechanical drum filter

Explanation

Nitrifying bacteria in the biofilter oxidize ammonia to nitrite and then nitrate in the two-step nitrification process. Mechanical filtration removes solids, UV disinfects, and foam fractionation strips dissolved organics.

Question 6Fisheries Technology (domain weights not published in source)

A fish farmer wants to induce spawning in common carp without killing broodstock. Which technique fits this requirement?

  1. Feeding a diet containing only plant protein
  2. Applying a cold shock to the brood pond
  3. Injecting a gonadotropin-releasing hormone analogue into the muscle or fin base Correct answer.
  4. Removing the pituitary gland surgically for later implantation

Explanation

GnRH analogues, often combined with a dopamine antagonist, induce ovulation while the broodfish survive and can be reused. Pituitary removal is destructive, cold shock is used for chromosome manipulation, and diet alone does not trigger spawning.

Question 7Fisheries Technology (domain weights not published in source)

Which measure best estimates the apparent feed conversion ratio of a fish population over a production cycle?

  1. Total protein fed divided by final biomass
  2. Total feed offered divided by final biomass
  3. Total weight gain divided by total feed offered
  4. Total feed offered divided by total wet weight gain Correct answer.

Explanation

The feed conversion ratio is feed consumed divided by live weight gained, so a lower value indicates more efficient conversion. The reciprocal is feed efficiency, and the other ratios do not express gain per unit feed.

Question 8Fisheries Technology (domain weights not published in source)

A grow-out cage holds 5,000 fish averaging 200 g. Daily ration is set at 3% of body weight. How much feed is required per day?

  1. 15 kg
  2. 3 kg
  3. 30 kg Correct answer.
  4. 300 kg

Explanation

Total biomass is 5,000 fish times 0.2 kg, which equals 1,000 kg. Three percent of 1,000 kg is 30 kg of feed per day.

Question 9Fisheries Technology (domain weights not published in source)

When sampling a pond with a cast net to estimate relative abundance, which practice most reduces bias?

  1. Using a single haul per sampling date
  2. Repeating hauls at the same time and location across sampling dates Correct answer.
  3. Selecting sites where fish were seen surfacing
  4. Sampling only the deepest point of the pond

Explanation

Consistent effort, timing, and location allow catches to be compared across dates without confounding from diel or spatial variation. Restricting to one site or one haul, or choosing sites by observed surfacing, introduces systematic bias.

Question 10Fisheries Technology (domain weights not published in source)

Which pathogen is most commonly associated with epizootic ulcerative syndrome in freshwater and estuarine fish?

  1. Infectious pancreatic necrosis virus
  2. Ichthyophthirius multifiliis
  3. Aphanomyces invadans Correct answer.
  4. Renibacterium salmoninarum

Explanation

Epizootic ulcerative syndrome is caused by the oomycete Aphanomyces invadans, which produces deep dermal ulcers. IPN is a viral disease, R. salmoninarum causes bacterial kidney disease, and Ichthyophthirius is the white spot ciliate.

Question 11Fisheries Technology (domain weights not published in source)

A farmer reports fish gasping at the surface at dawn with no other clinical signs. Which interpretation is most consistent with pond dynamics?

  1. Acute copper toxicity from an algicide overdose
  2. Night-time oxygen depletion from respiration exceeding photosynthesis Correct answer.
  3. Excess dissolved oxygen from midday algal supersaturation
  4. Low water temperature reducing metabolic demand

Explanation

At night, algal and fish respiration consume oxygen without photosynthetic production, so dissolved oxygen reaches its minimum near dawn and fish gasp at the surface. Supersaturation, toxicity, and cold water do not match the dawn-only pattern.

Question 12Fisheries Technology (domain weights not published in source)

Which statement correctly describes the role of dietary protein in fish feeds?

  1. It is used only as a binder to hold pellets together.
  2. It supplies essential amino acids for tissue growth and is the main energy source in many fish. Correct answer.
  3. It provides the bulk of dietary energy in all species regardless of feeding habit.
  4. It is required only during larval stages and can be omitted in grow-out diets.

Explanation

Protein supplies essential amino acids for growth and, in many fish, is the principal energy source, so its level and amino acid balance are critical. Protein is not merely a binder and remains essential through grow-out.

Question 13Fisheries Technology (domain weights not published in source)

Why is the amino acid methionine often added to soybean-meal-based fish diets?

  1. It is the most abundant amino acid in fish meal.
  2. It improves pellet water stability.
  3. It is the first limiting amino acid in soybean meal for many fish species. Correct answer.
  4. It acts as a vitamin precursor in the diet.

Explanation

Soybean meal is deficient in sulfur amino acids, and methionine is typically first limiting for fish, so supplementation restores amino acid balance. It is not a vitamin precursor and does not serve as a pellet binder.

Question 14Fisheries Technology (domain weights not published in source)

Which method is appropriate for determining the age of a scaly freshwater fish such as common carp?

  1. Counting annuli on scales or otoliths Correct answer.
  2. Measuring total body length only
  3. Weighing the liver
  4. Counting fin rays

Explanation

Annuli on scales or otoliths record seasonal growth and provide age estimates. Length, liver weight, and fin-ray counts do not record annual growth increments.

Question 15Fisheries Technology (domain weights not published in source)

In a pond, a sudden phytoplankton crash turns the water clear and ammonia rises. Which sequence best explains the ammonia increase?

  1. Reduced fish respiration lowering ammonia excretion
  2. Higher pH converting ammonium to nitrate
  3. Increased algal photosynthesis consuming ammonium
  4. Loss of algal nitrogen uptake plus decomposition of dead algae releasing ammonium Correct answer.

Explanation

Algae normally take up nitrogen, and their death adds organic matter that bacteria mineralize to ammonium, while nitrification may be oxygen-limited. Photosynthesis would consume ammonium rather than release it, and pH shifts do not convert ammonium to nitrate.

Question 16Fisheries Technology (domain weights not published in source)

Which practice best reduces the risk of introducing pathogens into a hatchery through live feed?

  1. Quarantining and disinfecting live feed cultures before use Correct answer.
  2. Mixing live feed from several farms to diversify
  3. Storing live feed at high density in the hatchery
  4. Feeding live feed immediately after harvest without treatment

Explanation

Live feed can carry bacteria and parasites, so quarantine and disinfection of cultures before use reduce introduction risk. Immediate feeding, dense storage, and mixing sources increase exposure.

Question 17Fisheries Technology (domain weights not published in source)

Which water parameter most directly limits the carrying capacity of a fertilized freshwater pond for phytoplankton?

  1. Total suspended solids
  2. Available phosphorus Correct answer.
  3. Water colour
  4. Dissolved silica

Explanation

Phosphorus is typically the limiting nutrient for phytoplankton in freshwater ponds, so fertilization programs target it. Silica limits diatoms only, and colour and suspended solids are indicators rather than the limiting nutrient.

Question 18Fisheries Technology (domain weights not published in source)

Which statement about the oxygen consumption of fish is correct?

  1. It is measured in milligrams per litre of pond water.
  2. It is independent of temperature within the normal range.
  3. It rises with temperature and activity and is commonly expressed per unit body weight. Correct answer.
  4. It falls sharply as water temperature rises.

Explanation

Metabolic rate, and thus oxygen consumption, increases with temperature and activity and is expressed as oxygen used per unit weight per unit time. It is not independent of temperature, does not fall with warming, and is not a concentration.

Question 19Fisheries Technology (domain weights not published in source)

A farmer wants to control excessive filamentous algae in a pond without harming fish. Which approach is most consistent with integrated pond management?

  1. Apply a full dose of copper sulfate at midday
  2. Stock additional herbivorous fish at very high density
  3. Reduce nutrient loading and shade or physically remove algae Correct answer.
  4. Increase fertilization to shade out the algae

Explanation

Reducing nutrient inputs and physically removing or shading algae address the cause with low risk to fish. Copper at full dose can deplete oxygen and stress fish, extra fertilization worsens the problem, and overstocking herbivores risks water quality decline.

Question 20Fisheries Technology (domain weights not published in source)

Which statement describes the primary purpose of aeration in intensive fish culture?

  1. To raise water temperature by heating the pond
  2. To remove nitrate by chemical precipitation
  3. To increase dissolved oxygen and promote gas exchange at the water surface Correct answer.
  4. To sterilize the water against pathogens

Explanation

Aeration adds oxygen and improves gas exchange, supporting higher stocking and feed loads. It does not heat water, precipitate nitrate, or sterilize pathogens.

Question 21Fisheries Technology (domain weights not published in source)

In a controlled breeding program, which method is used to produce triploid fish?

  1. Crossing two distinct species
  2. Applying a pressure or heat shock shortly after fertilization to retain the second polar body Correct answer.
  3. Feeding a diet supplemented with hormones during grow-out
  4. Rearing larvae at very low density

Explanation

Triploidy is induced by pressure or heat shock soon after fertilization, which blocks second polar body extrusion and yields three chromosome sets. Hormones, hybridization, and larval density do not alter ploidy.

Question 22Fisheries Technology (domain weights not published in source)

Which indicator best reflects the efficiency of a pond fertilization program?

  1. Total hardness above 500 mg/L
  2. Dissolved oxygen supersaturation at dawn
  3. Secchi disk transparency within a target range Correct answer.
  4. Water temperature exceeding 25 degrees Celsius

Explanation

Fertilization aims to maintain a plankton bloom that keeps Secchi transparency in a target range, indicating adequate but not excessive fertility. Temperature, high hardness, and dawn supersaturation are not fertilization-efficiency indicators.

Question 23Fisheries Technology (domain weights not published in source)

Which sampling gear is most appropriate for collecting benthic macroinvertebrates to assess pond bottom conditions?

  1. A cast net
  2. An Ekman grab Correct answer.
  3. A surface plankton net
  4. A gill net

Explanation

An Ekman grab samples a fixed area of bottom sediment and its associated benthic fauna. Plankton nets target the water column, cast nets capture fish, and gill nets are passive fish gears.

Question 24Fisheries Technology (domain weights not published in source)

A fish population shows a sex ratio heavily skewed toward males in a pond stocked for reproduction. Which explanation is most plausible for a species with environmental sex determination?

  1. Dissolved oxygen was supersaturated at midday
  2. Total alkalinity exceeded 200 mg/L
  3. Water temperature during early development shifted the sex ratio Correct answer.
  4. Feed conversion ratio was unusually high

Explanation

In species with temperature-dependent sex determination, incubation temperature during early development can skew the sex ratio. Feed conversion, oxygen, and alkalinity do not determine gonadal sex in these species.

Question 25Fisheries Technology (domain weights not published in source)

Which statement about the use of antibiotics in fish farming is correct?

  1. They require no withdrawal period because fish metabolize drugs quickly.
  2. They should be used only on veterinary diagnosis and with withdrawal periods observed before harvest. Correct answer.
  3. They are effective against viral diseases such as infectious pancreatic necrosis.
  4. They can be used continuously at low dose to prevent all diseases.

Explanation

Prudent use requires diagnosis, correct dosing, and adherence to withdrawal periods so residues do not reach the market. Antibiotics do not treat viruses, continuous low-dose use promotes resistance, and withdrawal periods are legally required.

Question 26Fisheries Technology (domain weights not published in source)

A hatchery technician needs to transport live tilapia fingerlings for six hours. Which practice best maintains survival during transport?

  1. Feed heavily just before loading to reduce stress during the journey
  2. Reduce dissolved oxygen and raise water temperature to lower metabolic rate
  3. Fast the fish before transport and keep transport water cool and well oxygenated Correct answer.
  4. Add a broad-spectrum antibiotic to the transport tank to prevent infection

Explanation

Fasting fish for 24 hours before transport reduces fecal fouling and oxygen demand in the transport water, while cooling and oxygenation lower metabolic stress. These combined measures are standard for live fish transport. Heavy feeding or antibiotics in the tank add waste and do not address transport stress.

Question 27Fisheries Technology (domain weights not published in source)

Which statement correctly describes the relationship between water temperature and dissolved oxygen in a freshwater pond?

  1. Warmer water holds more dissolved oxygen and supports higher fish biomass
  2. Dissolved oxygen is determined only by atmospheric pressure, not temperature
  3. Temperature has no measurable effect on oxygen solubility in freshwater
  4. Warmer water holds less dissolved oxygen, reducing the oxygen available to fish Correct answer.

Explanation

Oxygen solubility in water decreases as temperature rises, so warm ponds hold less dissolved oxygen at saturation. This is why summer afternoons and warm nights are the highest-risk periods for oxygen depletion in intensive ponds.

Question 28Fisheries Technology (domain weights not published in source)

A farmer wants to estimate the standing stock of fish in a pond where the pond volume is known and a representative sample can be taken. Which approach is most appropriate?

  1. Measure total pond volume and divide by the average fish weight
  2. Count all fish individually by draining and seining the entire pond
  3. Multiply the average fish weight by the estimated number of fish, derived from catch per unit effort Correct answer.
  4. Estimate stock from the amount of feed consumed over one week

Explanation

Standing stock is the product of mean individual weight and population number. Population number is commonly estimated from catch per unit effort or mark-recapture data, then multiplied by mean weight to obtain biomass.

Question 29Fisheries Technology (domain weights not published in source)

Which statement best describes the role of lipids in fish nutrition?

  1. Lipids are the primary source of digestible carbohydrate in fish diets
  2. Lipids supply essential fatty acids and concentrated energy, sparing protein for growth Correct answer.
  3. Lipids are inert bulk that provides no energy to fish
  4. Lipids serve mainly as a source of essential amino acids

Explanation

Dietary lipids are a concentrated energy source and supply essential fatty acids such as EPA and DHA that fish cannot synthesize in sufficient amounts. When energy from lipid is adequate, dietary protein is spared for tissue growth rather than being oxidized for energy.

Question 30Fisheries Technology (domain weights not published in source)

A pond manager observes a dense green surface scum that forms thick mats and produces a foul odor. Which organism group is most likely responsible?

  1. Diatoms such as Cyclotella
  2. Cyanobacteria forming surface blooms Correct answer.
  3. Zooplankton such as Daphnia
  4. Green algae such as Chlorella

Explanation

Cyanobacteria commonly form dense surface scums and can produce odor compounds and toxins. Their bloom-forming behavior and scum formation distinguish them from most green algae and diatoms.

Question 31Fisheries Technology (domain weights not published in source)

Which practice best reduces the risk of oxygen depletion in a heavily stocked pond during a warm, cloudy period?

  1. Applying a copper-based algicide to clear the water
  2. Applying a phytoplankton fertilizer to boost oxygen production
  3. Increasing the daily feeding rate to promote fish growth
  4. Reducing or suspending feeding and running aerators at night Correct answer.

Explanation

During cloudy weather, photosynthesis declines while respiration continues, so oxygen can fall sharply. Cutting feed reduces oxygen demand from digestion and waste, and night aeration maintains oxygen when photosynthesis stops.

Question 32Fisheries Technology (domain weights not published in source)

Which statement about the use of vaccines in finfish aquaculture is correct?

  1. Vaccination is generally most effective when fish are healthy and handled with minimal stress Correct answer.
  2. Vaccines provide immediate protection within hours of administration
  3. Vaccines eliminate the need for good biosecurity and water quality management
  4. All fish vaccines are administered by injection into the body cavity of fry

Explanation

Vaccine efficacy depends on a functional immune system, so healthy fish and careful handling improve protection. Vaccination complements, but does not replace, biosecurity and water quality management.

Question 33Fisheries Technology (domain weights not published in source)

Which measure is the most direct indicator of the survival rate of stocked fingerlings in a nursery pond?

  1. The amount of feed applied over the culture period
  2. The number harvested divided by the number stocked Correct answer.
  3. The average weight of fingerlings at harvest
  4. The plankton density measured at mid-culture

Explanation

Survival rate is calculated by dividing the number of fish harvested by the number originally stocked. The other measures describe growth, feeding, or pond productivity rather than survival.

Question 34Fisheries Technology (domain weights not published in source)

A fish farmer notices that a batch of fry shows a sharply swollen abdomen, spiral swimming, and a distended swim bladder. Which condition is most consistent with these signs?

  1. Infestation by external crustacean parasites
  2. Swim bladder disease associated with gas supersaturation or infection Correct answer.
  3. Nutritional deficiency of vitamin C
  4. Bacterial gill infection

Explanation

Distended swim bladder and spiral swimming point to swim bladder dysfunction, which can arise from gas supersaturation or infection. The other listed conditions do not produce this specific combination of signs.

Question 35Fisheries Technology (domain weights not published in source)

Which statement about the biological oxygen demand of pond water is correct?

  1. BOD is highest in clean, low-nutrient water
  2. BOD is unrelated to feed waste and fish excretion
  3. BOD reflects the oxygen consumed by microorganisms decomposing organic matter Correct answer.
  4. BOD measures the oxygen produced by phytoplankton during the day

Explanation

Biological oxygen demand quantifies oxygen consumed by microbes breaking down organic matter. Feed waste and fish excretion raise organic loading, which increases BOD and lowers oxygen available to fish.

Question 36Fisheries Technology (domain weights not published in source)

A farmer wants to improve the digestibility of a plant-based diet for a carnivorous fish. Which strategy is most appropriate?

  1. Replace fish meal with raw soybean meal without processing
  2. Add more cellulose as a binder
  3. Increase the crude fiber content of the diet
  4. Use extrusion or heat treatment to inactivate anti-nutritional factors Correct answer.

Explanation

Heat treatment and extrusion inactivate anti-nutritional factors in plant ingredients and improve starch and protein digestibility. Increasing fiber or using raw soybean meal reduces digestibility for carnivorous fish.

Question 37Fisheries Technology (domain weights not published in source)

Which method is most suitable for estimating the population size of fish in a pond using marked and recaptured individuals?

  1. Hepatosomatic index calculation
  2. Gonadosomatic index calculation
  3. Petersen mark-recapture estimate Correct answer.
  4. Condition factor calculation

Explanation

The Petersen method estimates population size from the ratio of marked to unmarked fish in a recapture sample. The other indices describe reproductive condition or body condition, not abundance.

Question 38Fisheries Technology (domain weights not published in source)

A pond is treated with lime to raise alkalinity. Which outcome is most likely if agricultural limestone is applied to a low-alkalinity pond?

  1. Alkalinity increases and pH buffering improves Correct answer.
  2. Alkalinity decreases and pH becomes more variable
  3. Phytoplankton growth stops completely
  4. Total hardness falls sharply

Explanation

Liming raises alkalinity and hardness, which improves pH buffering and stabilizes the pond against wide daily pH swings. Better buffering generally supports more stable phytoplankton production rather than stopping it.

Question 39Fisheries Technology (domain weights not published in source)

Which statement about the use of probiotics in aquaculture is correct?

  1. Probiotics are live microorganisms intended to improve the microbial balance of the host or rearing water Correct answer.
  2. Probiotics are synthetic antibiotics used to treat bacterial infections
  3. Probiotics are chemical disinfectants that sterilize pond water
  4. Probiotics are hormones that induce spawning

Explanation

Probiotics are live microbial supplements that can improve digestion, compete with pathogens, and enhance water quality. They are not disinfectants, hormones, or antibiotics.

Question 40Fisheries Technology (domain weights not published in source)

A technician needs to determine the fecundity of a female broodfish. Which measurement is most appropriate?

  1. Count the total number of eggs in a weighed subsample of ovarian tissue and scale up to total ovary weight Correct answer.
  2. Measure the ovary length with a ruler
  3. Measure the diameter of the largest egg only
  4. Record the gonadosomatic index only

Explanation

Fecundity is estimated by counting eggs in a representative weighed subsample and extrapolating to the total ovary weight. This gravimetric method accounts for the whole ovary rather than a single measurement.

Question 41Fisheries Technology (domain weights not published in source)

Which statement about the relationship between stocking density and fish growth in a pond is correct?

  1. Stocking density has no effect on dissolved oxygen demand
  2. Beyond an optimal density, competition for oxygen, feed, and space reduces individual growth Correct answer.
  3. Growth always increases as stocking density rises because more fish share the available feed
  4. Higher density reduces total feed requirement per pond

Explanation

At low to moderate densities, total yield rises with stocking, but beyond an optimum, competition and deteriorating water quality reduce individual growth and may lower survival. Density therefore has an optimum rather than a monotonic effect.

Question 42Fisheries Technology (domain weights not published in source)

A hatchery manager wants to reduce the risk of egg fungal infections during incubation. Which practice is most appropriate?

  1. Treat eggs with an approved antifungal agent and maintain clean, flowing water Correct answer.
  2. Increase organic matter around the incubator to provide nutrients
  3. Reduce water flow to keep eggs undisturbed
  4. Raise water temperature sharply to kill fungi

Explanation

Fungal infections such as Saprolegnia thrive on dead eggs and organic matter, so removing dead eggs, using approved antifungal treatments, and maintaining clean flowing water reduce risk. High temperature or stagnant water can increase stress and mortality.

Question 43Fisheries Technology (domain weights not published in source)

Which statement about the use of recirculating aquaculture systems is correct?

  1. Solids removal is unnecessary in recirculating systems
  2. Recirculating systems eliminate the need for biofiltration
  3. Biofilters in recirculating systems convert ammonia to nitrite and then to nitrate Correct answer.
  4. Recirculating systems require no water quality monitoring because water is reused

Explanation

Nitrifying bacteria in biofilters oxidize toxic ammonia to nitrite and then to less toxic nitrate. Recirculating systems still require solids removal, water quality monitoring, and periodic water exchange.

Question 44Fisheries Technology (domain weights not published in source)

A farmer observes that fish in a pond are feeding poorly and gill tissue shows brownish deposits. Which water quality problem is most likely?

  1. Excess dissolved oxygen
  2. Low nitrate concentration
  3. High iron concentration causing gill deposits Correct answer.
  4. Low water hardness

Explanation

Elevated iron in water can precipitate on gills as brownish deposits, impairing respiration and reducing feeding. Low hardness, high oxygen, and low nitrate do not produce this sign.

Question 45Fisheries Technology (domain weights not published in source)

Which statement about the use of hormones in fish breeding is correct?

  1. Hormones are used to induce ovulation in broodstock that do not spawn spontaneously in captivity Correct answer.
  2. Hormones are used to increase dissolved oxygen in ponds
  3. Hormones are used to sterilize pond water
  4. Hormones are used to change the genetic sex of all offspring

Explanation

Hormonal induction, using agents such as HCG or GnRH analogues, is used when broodstock fail to spawn naturally under culture conditions. Hormones do not sterilize water or directly control dissolved oxygen.

Question 46Fisheries Technology (domain weights not published in source)

A technician is asked to determine the proximate composition of a formulated fish feed. Which method is appropriate for measuring crude protein content?

  1. Dry ashing in a muffle furnace
  2. Bomb calorimetry
  3. Kjeldahl digestion followed by nitrogen determination and conversion to protein Correct answer.
  4. Soxhlet extraction with organic solvent

Explanation

Crude protein is determined by measuring nitrogen content, typically with the Kjeldahl method, and multiplying by a conversion factor. The other methods measure lipid, ash, or energy content.

Question 47Fisheries Technology (domain weights not published in source)

A farmer wants to control excessive growth of submerged aquatic weeds in a pond without harming fish. Which approach is most appropriate?

  1. Drain the pond completely during the growing season
  2. Add fertilizer to shade out the weeds
  3. Introduce herbivorous fish such as grass carp at a controlled stocking rate Correct answer.
  4. Apply a herbicide at the maximum label rate without considering oxygen demand

Explanation

Grass carp are herbivorous and can control submerged vegetation when stocked at an appropriate rate. Herbicide-killed plants decompose and can deplete oxygen, so biological control is often safer.

Question 48Fisheries Technology (domain weights not published in source)

A fish population is being assessed for growth. Which measure best describes the relationship between length and weight in a fish stock?

  1. The length-weight relationship expressed as W = aL^b Correct answer.
  2. The hepatosomatic index
  3. The gonadosomatic index
  4. The condition factor only

Explanation

The length-weight relationship, expressed as W = aL^b, describes how weight scales with length and allows estimation of weight from length. The condition factor is derived from this relationship but is a single index, not the full relationship.

Question 49Fisheries Technology (domain weights not published in source)

A pond experiences a sudden phytoplankton die-off after a period of dense bloom. Which sequence best explains the resulting oxygen decline?

  1. Dead algae release oxygen during decomposition
  2. Bacterial decomposition produces oxygen that offsets the loss
  3. Algae die, oxygen rises, and fish consume more oxygen
  4. Dead algae decay, bacteria consume oxygen, and oxygen falls while respiration continues Correct answer.

Explanation

When algae die, bacterial decomposition of the organic matter consumes oxygen, and the loss of photosynthetic oxygen production compounds the decline. Respiration by remaining organisms continues, so oxygen can fall rapidly.

Question 50Fisheries Technology (domain weights not published in source)

A farmer wants to prevent the development of antimicrobial resistance in pond-cultured fish. Which practice is most consistent with responsible antimicrobial use?

  1. Use antibiotics only when prescribed after diagnosis and follow the full course at the correct dose Correct answer.
  2. Use antibiotics prophylactically at low doses throughout the culture period
  3. Use antibiotics to promote growth in all fish
  4. Combine multiple antibiotics routinely to broaden coverage

Explanation

Responsible use means treating only diagnosed bacterial infections, following the prescribed dose and duration, and observing withdrawal periods. Prophylactic low-dose or routine growth-promoting use selects for resistant bacteria.