Mycotoxins in Aquaculture

Rui Gonçalves, Michele Muccio, Anneliese Müller

• Publisher: 5m Books
• Year: 2019
• ISBN:
  9781789180794
• Topic: Technology & Engineering
• Subtopic: Fisheries & Aquaculture
• Index: Technology & Engineering

With the current trend for the replacement of the fishmeal content of aquaculture feeds, the issue of antinutrients contained in plant-based materials is of growing concern in aquaculture production. Mycotoxins are known antinutrients; however, their role in aquaculture feeds has still to be fully elucidated. The interest of the scientific community towards these toxic metabolites is increasing, with a large number of recently published studies.Mycotoxins in Aquaculture is a comprehensive guide, commencing with a chapter covering general concepts, to help the reader to become familiar with the topic. The book then proceeds to cover the potential implications of the presence of mycotoxins, with chapters on aquatic species defense mechanisms, mycotoxins in aquaculture and in feeds, the analysis of mycotoxin content in commodities and feeds, and fighting mycotoxins. This important book brings together the authors' experience from work with terrestrial animals to identify the targets of these antinutrients in aquatic species.Mycotoxins in Aquaculture aims to help producers in their daily challenges and, at the same time, to contribute to the scientific community, by offering a new tool to whoever is approaching aquaculture in this era of finite resources.

01

Mycotoxins – general concepts

Karin NAEHRER
Edited by Anneliese Mueller

© Shutterstock, Kaulitzki

1.1 What are mycotoxins?

Mycotoxins are naturally occurring secondary metabolites produced by certain molds/fungi. Whereas primary metabolites (e.g. amino acids, sugars, etc.) are essential for the survival of organisms, the benefit of many secondary metabolites, such as mycotoxins, is not fully understood. Mycotoxins are chemical compounds of low molecular weight and low immunogenic capacity (Mallmann and Dilkin, 2007). There are some secondary metabolites of fungal origin with medicinal or industrial applications, for example, penicillin, but many exert detrimental effects on human and animal health, and animal productivity. Unfortunately, mycotoxins are known to contaminate crops and consequently animal feeds and animal products. In addition to the negative impacts on health, their presence can lead to significant economic losses. Crops with large amounts of mycotoxins often have to be destroyed (Vila-Donat et al., 2018). The mycotoxins that cause the biggest economic impacts on animal production are aflatoxins (Afla), trichothecenes (namely deoxynivalenol [DON] and T-2 toxin [T-2]), zearalenone (ZEN), ochratoxin A (OTA), fumonisins (FUM) and ergot alkaloids (Ergots). The focus of this book will be on these mycotoxins.

1.2 Mycotoxin-producing fungi

In general, the process of mycotoxin production by fungi is not well understood. Fungi, just like any living organism need nutrients to survive and they might have to compete for plant nutrients with the plant itself as well as with other microorganisms. Thus, mycotoxins may allow the fungus to prevail in adverse conditions by conferring a competitive advantage over other organisms (Rankin and Grau, 2002). Some insights on the effect of mycotoxins on the host plant have been gained for the mycotoxin DON: Its production has been found to prevent the formation of a thick cell wall, which could help the plant to avoid fungal infection. Furthermore, its production has been reported to be induced as a response to host defenses. Deoxynivalenol has also been observed to help the fungi to infect further until now healthy plant parts (Khaneghah et al., 2018). Unfortunately, even if we cannot entirely explain the reasons for their existence, mycotoxins are produced during different stages of food and feed production and are a serious problem worldwide.

Conditions suitable for fungal growth can occur at all times during crop growth, harvest and storage. Fungal species can be roughly categorized as field molds, which infect crops as parasites and storage fungi, which grow in feedstuffs stored under sub-optimal conditions.

Field fungi such as Fusarium spp. generally require higher moisture levels (> 0.9 water activity) to grow and produce mycotoxins. Therefore, they mainly infect seeds and plants in the field. Storage fungi such as Aspergillus spp. and Penicillium spp. require lower water activity and are thus more prominent after harvest and during storage (see Chapter 1.3).

Infection by Claviceps spp. and Neotyphodium spp. occurs only in the field. Claviceps are plant pathogens that replace plant structures such as grain kernels with hardened fungal tissues called ergots or sclerotia (Tudzynski et al., 2001). Sclerotia are a protection mechanism of the fungus allowing it to survive adverse environmental conditions. The sclerotia subsequently produce conidiospores and sugar containing secretions to attract insects and favor dispersion of spores to new hosts. In autumn, the sclerotia fall to the ground and overwinter until the following spring. Infection is usually favored by a cold winter followed by a wet spring. The fungus uses the nutrients from the plant for the development of the sclerotia and the production of Ergots. Sclerotia often contain a broad range of Ergots. The Claviceps genus, mainly Claviceps purpurea, parasitizes more than 600 plant species including some economically important cereal grains such as rye, wheat, barley, millet and oats (Strickland et al., 2011). In addition, ergot contamination in sorghum due to Claviceps africana has been discovered: here the Claviceps spores germinate and grow into the unfertilized seed producing a sclerotium (Krska and Crews, 2008).

Ergot alkaloids cause a disease known as ergotism, which was one of the first recognized mycotoxicoses (CAST, 2003; Flieger et al., 1997). The alkaloid pattern and individual alkaloid content of sclerotia vary largely according to fungal strain, host plant, differences in the maturity of the sclerotia, geographical regions and weather conditions (European Food Safety Authority [EFSA], 2011a).

In Table 1.1 the most important mycotoxin-producing fungi and their mycotoxins are listed. Some substances listed in Table 1.1 are so called “emerging mycotoxins”, for example, moniliformin (see Chapter 1.6).

Table 1.1 – The most important mycotoxins and their producers
Source: www.mycotoxins.info

1.3 Conditions for fungal growth and mycotoxin production

Mycotoxins occur worldwide. However, geographic and climatic factors affect the production and thus the occurrence of individual mycotoxins (Kuiper-Goodman, 2004). Preferences for a certain temperature range and water activity for growth and mycotoxin production have been observed for some fungal species (Table 1.2) (CAST, 2003; FAO, 2004; Hussein and Brassel, 2001; Marth, 1992; Ribeiro et al., 2006; Sanchis, 2004; Sweeney and Dobson, 1998). Water activity describes the water availability more precisely than the moisture content and is “the ratio of the water vapor pressure above the grains to that above pure water at the same temperature and pressure” (Mannaa and Kim, 2017: 245).

For instance, for the growth of F. graminearum, the optimum temperature and the minimum water activity have been estimated to be 24–26°C and 0.90, respectively (Sweeney and Dobson, 1998). The production of trichothecenes and ZEN by this fungal species is ubiquitous, but more prevalent in warm and moderate climates.

Aspergillus ochraceus grows at temperatures of 8–38°C and produces OTA within the temperature range 12–37°C. Temperature optima for growth and OTA production are 24–37°C and 31°C, respectively.

Penicillium verrucosum grows within the temperature range 0–31°C (optimum 20°C) and at a minimum water activity of 0.80. The temperature optimum for growth and OTA production is 20°C. However, OTA production occurs over the whole temperature range and significant quantities of the toxin can be produced at a temperature as low as 4°C and a water activity as low as 0.86 (Sweeney and Dobson, 1998).

Fusarium verticillioides and F. proliferatum growing on corn showed an optimum temperature for FUM production between 15 and 25°C (Samapundo et al., 2005).

Favorable environmental conditions, such as warm temperatures, high rainfall and humidity and a high soil fertility, increase the abundance of Claviceps spp. and the production of Ergots (Strickland et al., 2011). Toxic alkaloid-containing ergot sclerotia are used for sexual reproduct...

Table of contents

• Cover
• Half Title
• Title
• Copyright
• Contents
• List of acronyms
• List of figures and tables
• Acknowledgement
• Introduction
• 1. Mycotoxins – general concepts
• 2. Aquatic species defense mechanisms
• 3. Mycotoxins in aquaculture
• 4. Occurrence of mycotoxins in aquaculture feed
• 5. Analyzing mycotoxin content in commodities/feeds
• 6. Fighting mycotoxins
• 7. References
• 8. Index