In September 2021, aquaculture nutrition scientists, Santosh P. Lall and Sadasivam J. Kaushik published a review on nutrition and metabolism of minerals in fish in the open access journal Animals. The authors said that the It is also to identify areas that require future research, particularly the trace elements.
Mineral nutrition of fish has received limited attention as compared to other nutrients. Therefore, the main focus of the current review is trace element nutrition and metabolism of fish with a brief discussion on major macrominerals (calcium, phosphorus and magnesium). To date, only the requirements for nine minerals have been investigated. They added that this review is focused on the absorption and the dietary factors that reduce their absorption from feed ingredients of plant and animal origin. Some diseases, such as cataracts, anemia and bone deformity, have been linked to dietary deficiency of minerals.
The essentiality of macrominerals (calcium, phosphorus, magnesium, sodium, potassium and chloride) and certain trace elements (cobalt, copper, iodine, iron, manganese selenium and zinc) have been confirmed in fish. Some of the other trace elements (arsenic, fluorine, nickel, lithium, lead, molybdenum, silicon and vanadium) considered essential for humans and animals based on the impairment of specific physiological functions have not been reported in fish.
The number of farmed crustaceans, freshwater and marine fish species has increased considerably, often a generalisation is made estimating their mineral requirements based on salmonids and certain freshwater species with proper consideration for the determination made on different types of diets (purified, semi-purified and practical diet) and the use of inorganic supplements with high bioavailability. In addition, fish feeds increasingly comprise alternate sources of plant-based feed ingredients as compared to previously widely used fish meal due to the increase in global aquaculture production and its limited supply.
“Obviously, there is a need to reassess the mineral requirements as well as their bioavailability from a wide range of plant feed ingredients as well as new alternate sources of feed ingredients compared to fish meal,” said Kaushik.
“Some factors to consider are that absorption of minerals may vary between fish species because of differences in gastric acid secretion in fish with stomach and agastric or stomachless fish; uptake of minerals from water; differences in methodology used to measure the mineral requirements and response criteria (such as growth, feed utilisation and changes in specific enzyme activities) and synergistic or antagonistic interactions.”
Authors also addressed the minerals discharge from the uneaten feeds, faeces, urine from hatcheries and culture operations. These affect water quality and particulate forms settle in pond/tank bottoms. Fishery by products and other ingredients can contribute a minor amount of Cd which can be ultimately deposited.
Optimum levels of essential macro- and microminerals are required for growth and maintenance of normal health of farmed fish. The authors noted that increased attention is certain micronutrients and immunostimulants to reduce susceptibility to various stressors and diseases, but the knowledge in this area for fish and shrimp is rather scant, as compared to that for animals and humans.
The review covered requirement, deficiency, toxicity and bioavailability for essential trace elements, copper (Cu) and Iron (Fe), and that of Manganese (Mn), Selenium (Se) and Zinc (Zn). Here are some points extracted from the review for each trace element:
- In the case of Cu, requirements are relatively low as compared to other trace elements. It is necessary to know the concentration of Cu in water, feed ingredients and tissue prior to requirement studies. An interaction of Cu and Se have been observed in the Atlantic salmon. With regards to toxicity, the mechanism of Cu toxicity differs in freshwater and seawater. The EU Commission has authorized maximum content of Cu in complete feed for salmonids and other fish species at 25 mg/kg.
- A meta-analysis of published information on Fe requirements of several fish species showed estimates for Fe requirements ranging from 60 to 166 mg/kg, with a wide variation for all parameters tested. It should be emphasized that weight gain alone may not provide a good estimate of Fe requirement. Little is known about the bioavailability of Fe from feed ingredients and inorganic/organic iron feed supplements for fish. There is also a need to standardize the method to predict the bioavailability of Fe in fish diets.
- Manganese requirements of fish range from 2.5 (channel catfish) to 25 mg/kg diet (cobia). Mn deficiency causes skeletal abnormalities in rainbow trout, carp and tilapia. High concentrations of dietary Mn supplementation (1 g/kg ) caused changes in feeding behaviour, a decrease in body Fe concentration and elevation in Zn concentration in the body and vertebrae of grouper. In Europe, the maximum limit for fish feed is 100 mg/kg.
- The minimum Se requirement of fish varies with the form of Se (inorganic or organic) ingested, Se availability from different feed ingredients from the diet, vitamin E content of the diet and concentrations of waterborne selenium. Fish meal represent the best natural source of Se among the common feedstuffs with concentrations ranging from 1–2.4 mg/kg with the exception of tuna and mackerel meals where concentrations may exceed 5 mg/kg diet. Until the initiatives to reduce the amount of fish meal with plant ingredients, Se supplementation of farmed fish diets was not considered necessary.
- A meta-analysis of published information on Zn requirements of several fish species showed estimates ranging from3 3.5–64.6mg/kg on the basis of different parameters tested. Although fish meal produced from whole fish (e.g., herring and capelin meal) is considered a good source of Zn (80 to 130 mg Zn/kg and other minerals, the concentration of Zn varies in meals produced from processing discards containing partial fish parts. A higher limit in fish feed has been set for salmonids (150 mg/kg g of diet) and other fish (100 mg/kg of diet) in Europe.
Other micro minerals -Iodine (I), Chromium (Cr), Cobalt (Co), Boron (B), Cadmium (Cd) and Arsenic (Ar) were covered to a lesser degree because of lack of available information. As for the other trace elements, they said that the biochemical functions of F, Li, Ni, Pb, Si and V) have been shown in animals and humans, but their dietary essentiality based on the defined criteria of physiological impairment has not been widely accepted. These minerals have been studied in fish mostly from physiological aspects of their uptake from water and toxicity.
Finally, the authors presented the following messages:
- Many gaps exist in the knowledge of mineral nutrition of fish and shrimp related to their dietary requirements, physiological functions, absorption from the gastrointestinal tract and bioavailability from feed ingredients.
- Extensive research on farm animals has demonstrated that mineral requirements differ at various stages of their production cycle, certain trace elements play important roles in immune functions and disease prevention and application of specific methodologies are useful to predict the bioavailability of minerals from feed ingredients; however, the research in these areas on fish is limited.
- Most known mineral requirements (Ca, P, Mg, Cu, Zn, Mn, Se) were determined for young fish. Many studies were short term and gave little consideration to the dietary intake or mineral status prior to the experimental period and to the effect that the previous diet may have on body stores at the commencement of the study.
- A shift from the use of fish meal as a major source of protein and minerals in feeds to proteins of plant origin and land animal products now requires better assessment of mineral bioavailability for improving feed formulation more precisely. There are also new trace element supplements available which require proper assessment of their rate of absorption and potential impact on fish performance.
- Additional reliable new data on mineral requirements of major farmed fish species are needed to generate reliable information for use in feed formulation.
Citation: Lall, S.P.; Kaushik, S.J. Nutrition and Metabolism of Minerals in Fish. Animals 2021, 11, 2711. https://doi.org/10.3390/ani11092711 (open access).
With regards to the shrimp, Kaushik said, “Published available data in shrimp show that, over the past decade, summarised in NRC (2011) there is not much concrete /specific data on requirements of shrimp for trace elements (except maybe for selenium), despite the large volume of farmed shrimp today.” Note: some information on trace elements in shrimp is available at preprints, https://www.preprints.org/manuscript/202108.0088/v1
He added, “There is definitely worth undertaking systematic / serious work with shrimp. A recent initiative is Truong HH, Moss AF, Bourne NA, Simon CJ. 2020. Determining the importance of macro and trace dietary minerals on growth and nutrient retention in juvenile Penaeus monodon. Animals, 10(11): 2086. https://doi.org/10.3390/ani10112086
This is also an open access paper.”
Nevertheless, Kaushik has kindly summarised some information on trace minerals in marine shrimp.
Copper: Davis et al. (1993) found that Pacific white shrimp Penaeus vannamei would require no more than 34 mg total Cu/kg diet and that high levels of dietary Cu levels did not have any adverse effects on growth or survival. In black tiger shrimp, P. monodon, Lee and Shiau (2002) established the dietary Cu requirement to be 15–21 mg Cu/kg diet. Based on immune response indicators, a dietary Cu requirement of about 10– 30 mg Cu/kg diet was established to elicit non-specific immune responses. When fed very high dietary Cu levels, an increase in dietary vitamin C improved growth, haemocyte respiratory burst response and prevented tissue Cu accumulation (Lee and Shiau, 2003)
Iron: Even a dietary level of around 12 mg Fe/kg diet was found to be sufficient for P. vannamei when fed practical diets and with diets containing processed land animal proteins, which are rich in Fe, there was no need for iron supplementation. High levels of dietary Fe did not appear to induce any adverse effects in P. vannamei (Davis et al. 1992; Morgan, 2013).
Manganese: Kanazawa et al. (1984) suggested that a dietary supply of Mn was not required for the Kuruma prawn P. japonicus. Similar observations were also made by Fa-Yi and Lawrence (1997) who found that there was no need for a dietary supplementation with Mn to P. vannamei.
Zinc: Studies by Shiau and Jiang (2006) showed 32-34 mg/kg for improved growth, but an increased supply (35-48 mg Zn/kg diet) led to beneficial effects in terms of non-specific immune responses. Shi et al (2021) showed that dietary organic zinc promoted growth, immune response and antioxidant capacity. But the optimal dietary zinc level required was estimated to be 104.8 mg/kg and even a higher dietary level (130.6 mg/kg) led to increased tissue zinc concentrations. Davis et al. (1993) showed that a dietary supplementation of 200 mg Zn/kg diet was required to maintain normal zinc levels in the hepatopancreas.
Selenium: Se requirement for maximum growth was established to be about 0.6-0.7 mg Se kg-1 diet for freshwater prawn (Kong et al. 2017) who also showed that higher dietary Se levels (>1.1 mg kg-1) were required to maximise body Se concentrations. In P. vannamei, a dietary supply of 0.45 mg/kg was found sufficient for improving growth (Yu et al. 2021) and higher levels (0.8 mg/kg diet) led to increased antioxidant enzyme activities but also led to stress and tissue damage. In the same species, a dietary supply of 0.43 to 0.45 mg Se/kg diet in the form of hydroxyl methionine selenium (HMSe) was likewise found to be effective (Wang et al. 2021) for maintaining high growth and an antioxidant response.
Santosh Lall (Retired) was with National Research Council of Canada, Halifax, NS Canada. Email: firstname.lastname@example.org
Sadasivam J. Kaushik (retired) was with INRA, St Pée sur Nivelle, France and subsequently with Ecoaqua Institute, Universidad de Las Palmas de Gran Canaria, Las Palmas, Spain. Email: email@example.com
Keywords: minerals; trace elements; fish; copper; iron; selenium; manganese; zinc; calcium; phosphorus; magnesium