Phenomenon of soil ingestion, or geophagy, attracts an attention of numerous researchers for years (Woywodt & Kiss, 2002). Geophagy is not exhibited everywhere, but it is widespread in many animals and human (for review, see Mahaney & Krishnamani, 2003; Limpitlaw, 2010).

Johns & Duquette (1991) suggest that the physiological significance of geophagy made it important in the evolution of human dietary behaviour.

More than 50 species of animals have been reported to ingest various types of clays, salt and other Earth materials, in particular at sites named "licks”. In general, this form of dietary behaviour allows an animal to provide its organism with the needed nutrients, solve gastrointestinal and intoxication problems, suppress some maladies and improve general vital indexes (Limpitlaw, 2010).

In particular, parrots are ones of the most studied soil-eaters (e.g., Gilardi et al., 1999; Brightsmith, 2004; Brightsmith et al., 2004, 2008).

Members of our group have started the first experiments with clay-eating in fishing in the end of 1980s, after lucky detectiing an open deposit of high quality white clay on an abrupt bank of the Dnipro river (localities in Ukraine). First of all, this clay was used to prepare fishing groundbaits (with an excellent attractive effect). In the subsequent years, four basic ways to use clay-eating in fishing (see below) were elaborated. Taking into account the current hazardous ecological situation in the most part of water bodies, we have decided to enter such technological products as the Dietary Clay Pellets & Dietary Clay Boilies into mass production.

In total, the following basic clayey products (of the white, green, yellow, orange and red colors) are elaborated:

1. Paste, or Plasticine

2. Polenta

3. Dietary Clay & Rice Pellets

4. Dietary Clay & Rice Boilies

In the latter two cases, the white processed rice (up to about 30 weight percent) has been used in the capacity of an extender and binder. This rice is lighter than the common rice meal and flakes. It quickly dissolves in the water. Yet, it is quickly digested in the intestines of fish. Recall also, rice products (without salt, sugar and spices) are widely and effectively used in the human diets.

To test dietary pellets and boilies, one week pre-baiting campaigns with the everyday morning and evening sessions were conducted in the field. For the first presentation in the 1st day, items enhanced with powder, liquid or spray attractants (one type within all sessions) were only used. In the 2nd, 3rd and 4th days, mixes of enhanced and non-enhanced items, taken in the percent ratio of 70:30, 50:50 and 30:70, were used. Finally, in the remaining days, non-enhanced pellets and boilies or even practically blank kaolin balls with small amount of binder were only offered.

According to our observations, to the end of the pre-baiting campaigns fish usually readily eat non-enhanced or blank clayey pellets (used for roach, Rutilus rutilus, and other relatively small fish) and boilies (used for carp, Cyprinus carpio), demonstrating in this way that they include these items in their natural, in water bodies with weak angling pressure, or semi-narural, in other cases, diets.

Generally, this form of dietary behaviour, named dietary self-selection or macronutrient self-selection, is determined by an individual experience of an animal and reflects the positive associations between some macronutrients and physiological state of this animal, which are established during its learning in the nature, aquaculture, zoo or laboratory (for review, see Moore et al., 2005; Huntingford et al., 2012). These macronutrients provide energy requirements, optimum protein, fat and carbohydrate levels, or, more specifically, vitamin, mineral and other requirements.

In respect of fish, the phenomenon of dietary self-selection has attracted an undivided attention of numerous researchers approximately from the second part of 1990s (e.g., Sánchez-Vázquez et al., 1999; Aranda et al., 2000, 2001; Yamamoto et al., 2001; Rubio et al., 2003; Vivas et al., 2003; Yamamoto et al., 2003). Of course, direct biochemical, trophological and biomedical investigations of clayey diets in fish will be useful to the further development of diet designing in aquaculture, fishing (baits, lures, groundbaits) and related areas.

Basic References

Aranda A., Sánchez-Vázquez F.J., Zamora S., Madrid J.A. 2000. Self-design of fish diets by means of self-feeders: validation of procedures. Journal of Physiology and Biochemistry 56, 155-166.

Aranda A., Sánchez-Vázquez F.J., Madrid J.A. 2001. Effect of short-term fasting on macronutrient self-selection in sea bass. Physiology & Behavior 73, 105-109

Brightsmith D. J. 2004. Effects of weather on parrot geophagy in Tambopata, Peru. Wilson Bulletin 116, 134-145

Brightsmith D. J., Aramburú R. 2004. Avian geophagy and soil characteristics in Southeastern Peru. Biotropica 36, 534-543

Brightsmith D. J., Taylor J., Phillips T.D. 2008. The roles of soil characteristics and toxin adsorption in avian geophagy. Biotropica 40, 766-774

Gilardi J.D., Duffey S.S., Munn C.A., Tell L.A. 1999. Biochemical functions of geophagy in parrots: Detoxification of dietary toxins and cytoprotective effects. Journal of Chemical Ecology 25, 897-922

Huntingford F., Jobling M., Kadri S. (Editors). 2012. Aquaculture and Behavior. Wiley-Blackwell, The Atrium, Southern Gate, Chichester, United Kingdom

Johns T., Duquette M. 1991. Detoxification and mineral supplementation as functions of geophagy. American Journal of Clinical Nutrition 53, 448-456

Limpitlaw U.G. 2010. Ingestion of Earth materials for health by humans and animals. International Geology Review 52, 726-744

Mahaney W.C., Krishnamani R. 2003. Understanding geophagy in animals: standard procedures for sampling soils. Journal of Chemical Ecology 29, 1503-1523

Moore B., Marsh K., Wallis I. 2005. Taught by animals: how understanding diet selection leads to better zoo diets. International Zoo Yearbook 39, 43-61

Rubio V.C., Sánchez-Vázquez F.J., Madrid J.A. 2003. Macronutrient selection through postingestive signals in sea bass fed on gelatine capsules. Physiology & Behavior 78, 795-803

Sánchez-Vázquez F.J., Yamamoto T., Akiyama T., Madrid J.A., Tabata M., 1999. Macronutrient self-selection through demand-feeders in rainbow trout. Physiology & Behavior 66, 45-51

Vivas M., Sánchez-Vázquez F.J., Garcia Garcia B., Madrid J.A. 2003. Macronutrient self-selection in European sea bass in response to dietary protein or fat restriction. Aquaculture Research 34, 271-280

Yamamoto T., Shima T., Furuita H., Shiraishi M., Sánchez-Vázquez F.J., Tabata M. 2001. Influence of decreasing water temperature and shortening of the light phase on macronutrient self-selection by rainbow trout Oncorhynchus mykiss and common carp Cyprinus carpio. Fisheries Science 67, 420-429

Yamamoto T., Shima T., Furuita H., Suzuki N. 2003. Effect of water temperature and short-term fasting on macronutrient self-selection by common carp (Cyprinus carpio). Aquaculture 220, 655-666

Woywodt A., Kiss A. 2002. Geophagia: the history of earth-eating. Journal of the Royal Society of Medicine 95, 143-146