ASRB NET: Fisheries and Aquaculture

ASRB NET Fisheries and Aquaculture covers fish biology, aquaculture, fish nutrition and fish pathology. Questions link water quality, feeding and disease.

Core concepts

• Fish osmoregulation differs between freshwater and marine species; euryhaline species tolerate salinity change, while stenohaline species do not.
• Aquaculture systems include pond, raceway, cage and recirculating aquaculture system (RAS); RAS controls ammonia and solids.
• Stocking density affects growth through oxygen, ammonia and social stress.
• Nutrition: feed conversion ratio, FCR = feed fed divided by live weight gain; lower FCR is better. Protein requirement is species- and stage-specific.
• Fish pathology: bacterial causes include Aeromonas and Edwardsiella, viral examples include IPN and WSSV in shrimp, and parasitic examples include Ichthyophthirius; diagnosis needs wet mount and culture or PCR.

Worked example

A pond receives 150 kg feed and fish gain 100 kg. FCR = 150 divided by 100 = 1.5. Feed efficiency = 1 divided by 1.5 = 0.67, or 67%. Reasoning: FCR compares input to output; a lower value means more efficient conversion. If mortality rises, FCR worsens because gain falls while feed input continues.

Traps that cost marks

• Reversing FCR and feed efficiency.
• Treating unionised ammonia, NH3, as equivalent to total ammonia nitrogen; NH3 toxicity rises with pH and temperature.
• Assuming all fish can be fed the same protein level.
• Diagnosing disease from a single moribund fish without water-quality data.