Sources: Janse et al. (2004), NRC (2011), and Hamre et al. (2013). © John Wiley & Sons.
| Nutrient | Juvenile teleost | Larval teleost | Elasmobranchs |
|---|---|---|---|
| Calcium (%) | 0.87 (0.34–2.00) | 0.5 | |
| Phosphorus (%) | 0.61 (0.33–0.80) | 0.70 | |
| Sodium (%) | 0.11 (0.06–0.15) | (0.1–0.3) | |
| Magnesium (%) | 0.05 (0.04–0.06) | 0.05 | |
| Potassium (%) | 0.53 (0.26–0.80) | (0.1–0.3) | |
| Chloride (%) | 0.16 (0.15–0.17) | (0.1–0.5) | |
| Copper (ppm) | 4.3 (3.0–5.0) | (1–4) | |
| Iodine (ppm) | 1.1 (1–1.1) | (100–300) | |
| Iron (ppm) | 88 (30–150) | (50–100) | |
| Manganese (ppm) | 9 (2–12) | 40 | (20–50) |
| Selenium (ppm) | 0.34 (0.15–0.70) | (1.4–3.0) | (0.15–038) |
| Zinc (ppm) | 23 (15–37) | (15–100) |
All values are on a dry matter basis and represent the mean (range) from published literature.
Iodine is important for all fish and functions as a component of thyroid hormones. The requirements of elasmobranchs for iodine are well‐described and deficiency is a common cause of goiters (Janse et al. 2004). Ozone filtration reduces the bioavailability of water‐based iodine (iodide) due to oxidation to the unavailable iodate (IO3−). Additionally, high nitrate levels or other goitrogenic compounds can reduce iodide uptake (Morris et al. 2011).
Mineral (and vitamin) requirements of elasmobranchs are not well‐defined. Few comprehensive studies have examined the vitamin and mineral content of their wild prey. A recent study of lemon shark prey items found that the daily Zn intake exceeded the minimum requirements for teleosts, while daily intake of Fe, Cu, and Mn was much lower than the minimal requirements for teleosts (Pettitt‐Wade et al. 2011). Daily intake was calculated as a percentage of total diet at 6.6% Ca, 1.1% Na, 1.0% K, 0.3% Mg, 0.008% Zn, 0.005% Fe, 0.0007% Cu, and 0.0001% Mn.
Other Additives
Other dietary compounds can modulate animal health or performance in fish. Work in fish has demonstrated benefits from immune stimulants, probiotics, and prebiotics.
Immune stimulants are naturally occurring compounds that can increase resistance to disease. Most, if not all, essential nutrients influence disease resistance, particularly vitamins C and E (Blazer and Wolke 1984; Verlhac and Gabaudan 1994). Within non‐nutrient compounds, β‐glucans are the most commonly reported immune stimulants. When fed at low levels (<0.2% of the diet), β‐glucans can modulate fish immune responses and improve survival following subsequent disease challenge, particularly for extracellular bacterial infections (Sinha et al. 2011; Hixson 2014). Other examples of immune stimulants include garlic and propolis (Sforcin 2007; Lee and Gao 2012). Short‐chain fatty acids such as propionate may also modulate immune responses in fish (Hoseinifar et al. 2016). Further information on immune stimulants is available in Chapter A12 and reviews such as Lall and Tibbetts (2009), Nayak (2010), Verhlac‐Trichet (2010), and Kiron (2012).
Probiotics are cultures of micro‐organisms intended to colonize or influence intestinal flora (Nayak 2010). Numerous microbes have been identified as probiotics in fish (Lactobacillus, Lactococcus, Leuconostoc, Enterococcus, Carnobacterium, Shewanella, Bacillus, Aeromonas, Vibrio, Enterobacter, Pseudomonas, Clostridium, and Saccharomyces spp.). Many help feed conversion efficiency and growth, modulate the immune response, and confer protection against pathogens (Burr et al. 2005; Nayak 2010; De et al. 2014). Stability in the diet and efficacy are both concerns and more research is needed.
Prebiotics are nondigestible food ingredients that benefit the host by stimulating established microbial activity in the GI system (Yousefian and Amiri 2009). They are usually carbohydrates that are resistant to gastric acidity, hydrolysis, and fermentation. Prebiotics include oligofructose, transgalactooligosaccharides (TOS), inulin, and lactulose. They have shown similar benefits to probiotics in feed efficiency, growth, and immune function, but more research is needed (Yousefian and Amiri 2009).
Nutrient Choice
There is some evidence that fish can select for certain nutrients when given dietary choices, particularly for macronutrients such as protein (da Silva et al. 2016). When fish could self‐select between protein (from casein and gelatin), lipid (from fish oil/soybean oil mix), and carbohydrate (from dextrin), selection varied by wild‐type feeding strategy. More carnivorous species selected for higher protein intake of 55–62% protein, 16–23% carbohydrate, and 16–22% lipid (Sánchez‐Vázquez et al. 1999; Rubio et al. 2003; Almaida‐Pagán et al. 2006). More omnivorous species selected lower protein intake levels: Nile tilapia ~45% protein, 32% carbohydrate, and ~22% lipid; and goldfish ~22% protein, 45% carbohydrate, and ~32% lipid (Sánchez‐Vázquez et al. 1998; Fortes‐Silva et al. 2011). Selection of lipid sources has also been demonstrated: tilapia selected flaxseed or fish oil‐based diets (sources of omega‐3 fatty acids) in preference to soybean oil‐based diets (omega‐6 fatty acids) (Fortes‐Silva et al. 2010). There is less evidence of selection for appropriate nutrient intake of vitamins or minerals in fish. An important caveat is that low quality food items may not allow for selection to occur, because of an inability to modify intake levels to meet nutrient needs (e.g. low‐protein diet), a net loss of nutrients (e.g. increased synthesis of microbial protein resulting in a net protein loss), and/or ingestion of toxins that may limit intake. An excellent discussion of these factors and the dietary choices of the herbivorous butterfish (Odax pullus) is presented by Baker et al. (2016).
Feeding
Diet Selection and Formulation
Diets should be palatable, free from contamination, and of sufficient quantity and quality. They should mimic wild diets where possible and provide variety and enrichment. Consideration should be given to the species, life stage, size, body condition, reproductive state, and/or disease state of each individual.
Diet formulation involves matching food items with the specific