A Guide to Acceptable Procedures Practices for Aquaculture Fisheries Research - Part 1

1. Animal husbandry

1.1. Basic husbandry

1.1.1. Facilities

‘Facilities’ includes the ponds, raceways, tanks, cages and aquaria in which animals are kept. Scientists and the investigators, ACEC's and fisheries research institutions are responsible for ensuring that facilities are appropriately staffed, designed, constructed, equipped, operated and maintained to achieve a high standard of animal care and to fulfil scientific requirements. The overall condition and management of facilities must permit effective maintenance and servicing and be compatible with maintaining the animals in good health.

Operation of facilities

All fish-holding facilities must be operated in a manner that optimises conditions for fish. Guidelines for the design and operation of fish hatcheries and aquaculture facilities are given in Rowland and Tully (2004) and Rowland et al. (2007). 

Appropriate stocking densities, aeration and water management must be used. All facilities should be aerated; tanks and aquaria continuously with diffused air or oxygen and ponds nightly for around 8 h/day with diffused air or mechanical aerators such as paddlewheels. At very high temperatures and feeding rates, or on overcast, still days, ponds may need to be aerated for longer periods or continuously. Cages should be located in aerated ponds.

In circular, self-cleaning tanks, a constant flow of water is used to facilitate the removal of solids and dissolved wastes (eg. ammonia) and to supplement aeration. If tanks need to be static, eg. during chemical treatment, fish should not be fed and water (10-30 %) should be exchanged daily. Tanks should be placed under cover or in a building out of direct sunlight to provide an environment with relatively low light intensity. It is beneficial to some species, eg. Murray cod, to partially cover tanks to reduce stress.

Static ponds should be managed (stocking densities, aeration, water quality, diseases, feeding etc.) according to guidelines for particular species, eg. techniques for the culture of silver perch have been published (Rowland and Bryant, 1995; Rowland et al., 2007).

Stocking densities 

Optimal stocking densities vary with a number of factors including culture unit (pond, tank, cage), species, size of fish, culture phase, water quality etc. The following table gives optimal and upper densities for the different units. 

Requires greater control of water quality, more experience and entails higher risk.

Monitoring requirements

All fish holding facilities and support systems must be inspected every 24 hours. Things to observe include changes to the fishes’ external body, especially any signs of diseases, abnormal swimming behaviour, abnormal feeding behaviour, as well as unexpected changes in he appearance of the water. Water quality variables and fish health need to be monitored regularly (see following). 

1.1.2. Nutrition and feeding 

Commercial diets are available from a number of feed manufacturers in Australia and overseas for marine and freshwater fish including diets for larvae, fry, fingerlings, juveniles and adults. Wherever possible, manufactured fish diets should be stored for as short a time as possible before use. If the diets are to be stored for longer than a month or two, they should be kept in cool (<15°C), dry conditions, or frozen. At all times, manufactured diets should be kept cool and dry. If there is any sign of fungal contamination, diets should be discarded. 

The manufactured diet should be designed for the target species, life-stage and size. The nutritional requirements of silver perch have been determined and practical diets formulated for silver perch (Allan and Rowland, 2002). Fresh or frozen bait fish or other aquatic plant or animal material are often used as a food source. They usually need to be stored frozen and care must be taken to ensure they are not contaminated and do not deteriorate. 

Fish should be fed to optimise survival, health and growth. Appropriate feeding strategies should be followed for each species, where available. Guidelines for feeding silver perch on restricted rations have been published (Rowland et al., 2001) and these would be good guidelines for other species. Under feeding will reduce growth and potentially compromise health, and excess feeding can adversely affect water quality. At such times feeding rates can be reduced or feeding suspended until water quality improves. Fish held in quarantine should not be fed. 

1.1.3. Water quality variables 

The water quality variables alkalinity, hardness, conductivity and metals are relatively stable and ‘characterise’ the water in which fish are held and grown. Dissolved oxygen, pH, ammonia and nitrite are unstable variables that are influenced by culture activities and can change rapidly. Other important variables are; temperature, salinity, nitrogen, hydrogen sulphide and turbidity. Each species will have an optimal range for each variable, as well as lethal limits. Details of each of these variables and their importance for holding and growing fish can be found in Rowland (1998) and much of the following summary is taken from that publication. 

Temperature 

Water temperature influences chemical and biological procedures. Fish are cold-blooded (poikilothermic) and so water temperature affects their metabolism, digestion, growth, sexual maturity and reproduction. Rates of chemical and biological reactions roughly double for every 10°C increase in temperature. As water temperature increases, fish become more active, consume more food, use more oxygen and grow faster. However, when the temperature exceeds the critical level for a particular species, fish become stressed, more vulnerable to disease, may stop growing and can die. 

Salinity 

Salinity refers to the total concentrate of all dissolved ions. As salinity rises, the ability of water to conduct electricity also increases and conductivity is therefore often used to measure or estimate salinity. In general, freshwater is 0-500 mg/L salinity and full seawater is 35 000 mg/L (or 35 g/L; the units are sometimes presented as ‘parts per thousand’, ppt or ‰). Many Australian native freshwater fish, such as silver perch, golden perch, Murray cod and catfish can tolerate long-term exposure up to at least 5 g/L salt, while many estuarine species such as mulloway and snapper can tolerate salinities down to as low as 10 g/L. Rainbow trout, 10 NSW Department of Primary Industries (Fisheries) ACEC, October 2015A Guide to Acceptable Procedures and Practices for Aquaculture and Fisheries Research Australian bass and barramundi can tolerate salinities of 0-35 g/L. When changing salinity, fish should be allowed to adjust slowly (eg. 1-5 g/L/day). Salt reduces stress, increases mucus production, promotes healing of damaged skin and kills some ectoparasites in freshwater fish. 

Dissolved oxygen 

Dissolved oxygen is the most critical and limiting variable in fish husbandry and aquaculture. Like all animals, fish cannot live without oxygen and lethal levels vary from just less than 1 mg/L to about 3 mg/L. Sub-lethal levels (eg. 2-4 mg/L) can stress fish, reduce growth and increase susceptibility to disease. Oxygen enters water through diffusion at the air-water interface and as a result of photosynthesis when there are plants (eg. algae) in the water. In ponds and natural waters, dissolved oxygen undergoes significant diurnal and seasonal fluctuations (see Rowland 1998). In aquaria, tanks and raceways, dissolved oxygen is usually maintained by aeration of the water using low pressure compressors or blowers (through diffusers like air stones). In ponds, paddle-wheel aerators are among the most efficient methods of transferring oxygen from the air to the water. Mechanical aeration creates currents and so assists with mixing water throughout the pond. 

pH and carbon dioxide 

The pH of water is the measure of the hydrogen ion concentration and indicates whether it is acidic (pH < 7), neutral (pH = 7) or alkaline (pH > 7). The desirable range for most species of fish is 6-9. A pH of 4 is lethal for most species, while prolonged exposure to pH levels of above 10 can be lethal. 

Carbon dioxide affects pH because it has an acidic reaction in water. Phytoplankton and other aquatic plants remove carbon dioxide (and produce oxygen) from water during photosynthesis in daylight hours and all organisms add carbon dioxide through respiration. Typically, in ponds or water bodies with algal blooms (phytoplankton) or other aquatic vegetation, the pH will rise during the day, peaking in the afternoon, then decline to a minimum around dawn. As with many water quality variables, the interaction of pH with other variables can be critically important. The inter-relationship of pH with ammonia is one of the most obvious examples (see following).