Feed requirements vary with diet, species, life history stage (e.g. juveniles require more energy per unit weight than adult fish); water quality (e.g. temperature, salinity); exercise level and habitat size; and social interactions (e.g. dominance hierarchy). In aquaculture, feed amount is calculated as a percentage of the total biomass of fish, with the percentage decreasing as the individuals grow. Rates for juvenile cultured species range from 4–11% BW, decreasing in adults to 0.5–2% BW, but this is highly species‐ and temperature‐dependent (New 1987). In aquarium‐maintained species, feed amounts can be more difficult to assess since the goal is longevity rather than production, and animals are often maintained in complex, multispecies systems. Generally, fish species in aquariums are fed at lower rates than those in aquaculture. In adult bony fish, 0.5–1% BW/day is a good starting point, as this is the average stomach volume of many bony fish. This should be reduced if the entire ration is not consumed within five minutes for individuals, or within 15 minutes for animals maintained in large groups. Food around the edges of the tank or settling on the bottom, or increases in ammonia, are signs of overfeeding and should be avoided. For adult elasmobranchs, starting food amounts have been outlined by Janse et al. (2004), with bottom‐dwelling sharks (e.g. Hemiscylliidae and Stegostomatidae), bottom‐dwelling rays (e.g. Dasyatidae), and ram‐ventilating rays (e.g. Myliobatidae) at 4–6% BW/week; slow‐swimming ram‐ventilating sharks (e.g. Odontaspididae) at 1.0–2.5% BW/week; and fast‐swimming ram‐ventilating sharks (e.g., Carcharhinidae) at 3–4% BW/week. Elasmobranchs with higher metabolic rates (e.g. Mobula spp.) or those that are more endothermic may require much higher rations than described above. Rations for juveniles should be multiplied by a factor of 1.5–3.0. Feeding amounts should be adjusted based on growth data, body weight and body condition comparisons with wild counterparts, and blood analyses where available (Janse et al. 2004).
Body Condition
Body condition scores (BCSs) are a useful way to assess the health and nutritional status of fish at a point in time. They are often designed with a 5‐point scale where 3 represents optimal condition and 1 and 5 represent under‐ and over‐conditioned animals, respectively.
Studies have evaluated body condition indices in wild and cultured fish by examining the relationship between body mass and body length (Kohler et al. 1995; Hussey et al. 2009). Visual BCS systems are more desirable in managed collections as they do not require fish handling for morphometrics. These have been published for zebrafish (Danio rerio) and spotted eagle rays (Aetobatus narinari) (Wilson et al. 2013; Kamerman et al. 2017). BCS systems for fusiform teleosts similar to koi (Cyprinus carpio koi), demersal rays similar to southern stingrays (Hypanus americanus), and pelagic sharks similar to requiem sharks (Carcharhinus spp.) are shown in Figures A4.1–A4.3. These are meant as a guide only, as different species will build fat and muscle in different anatomical locations.
Since body condition scores are subjective, they are best assessed by a team of people (e.g. husbandry staff, technicians, veterinarians, and nutritionists). They are particularly useful when compared across a group or across time, especially during periods of physiologic change (e.g. around breeding and growth).
Food Storage and Preparation
Appropriate food storage and handling are crucial. All aspects of the feeding program should be evaluated to ensure that offered food items are free of contamination (biological, chemical, and physical) and are stored, thawed, prepared, and fed in a manner that preserves nutritional quality.
Food Safety and Monitoring
Hazard Analysis and Critical Control Point (HACCP) programs can be applied to the entire food handling pathway from harvest, catch, or manufacturing through animal consumption (Schmidt et al. 2006). These can help ensure food safety with regard to biological (pathogenic micro‐organisms or parasites), chemical (natural toxins, pesticides, drug residues, manufactured chemicals), or physical contamination (foreign objects). HACCP programs involve the following steps:
1 Identify potential hazards or risks within the system.
2 Identify critical control points in the system where hazards could occur.
3 Establish critical limits for each potential hazard.
4 Establish monitoring of the control points.
5 Establish corrective measures when critical limits are exceeded.
6 Develop record‐keeping and verification methods.
To ensure the best‐quality diets, each facility should develop their own HACCP programs and ask their vendors to share their HACCP programs. Readers are referred to Schmidt et al. (2006) and Henry et al. (2010) for further discussions on developing and implementing HACCP programs.
Storage
High standards for food storage prevent nutrient loss and product degradation. Temperature, humidity, air exposure, and lighting can all affect food quality.
Frozen foods should be stored between −30 and −18°C (−22 and 0°F) in order minimize oxidation and thiaminase activity (Crissey 1998; Henry et al. 2010). Refrigeration at <4°C (39°F) should be used for storing vegetables, fruits, forage, and for short‐term holding (<24 hours) of thawed seafood and gel foods. Some pelleted and flake foods also require refrigeration. Room temperature storage, e.g. 18–21°C (64–70°F) and 50–60% relative humidity, can be used for some dry foods. The foods should be off the ground and the area should be well‐ventilated (Henry et al. 2010). Temperatures of food storage locations should be monitored and recorded routinely to ensure conditions are suitable.
It is common to purchase food in bulk and store items until use. Using sealed containers to minimize air and light exposure helps maintain nutrient content. It is important that containers are labeled with the:
Date of catch, manufacture, or receipt.
Date of opening.
Date of discard.
The discard date, or shelf life, should be provided by the manufacturer for pelleted, flake, and gel foods. For frozen seafood, the discard date should be less than 12 months from catch. This may be reduced to six months for high‐fat foods (e.g. mackerel and herring) but nutritional testing is a more reliable way of evaluating nutrient losses.
Figure A4.1 Body condition score system for koi (Cyprinus carpio koi) and similar fusiform fish.
Source: Image courtesy of Amanda Slade; copyright reserved.
Figure A4.2 Body condition score system for southern stingrays (Hypanus americanus) and similar demersal rays.
Source: Image courtesy of Amanda Slade; copyright reserved.
Figure A4.3 Body condition score system for reef sharks (Carcharhinus sp.) and similar pelagic sharks.
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