Phytochemicals such as alkaloids, flavonoids, pigments, phenolics, terpenoids, steroids and essential oils are a large group of plant-derived compounds commonly found in diets high in fruits, vegetables, beans and cereals. Plant remedies are closely linked to the maintenance of good health in the cultural heritage of many countries. Despite the potential benefits to health and performance as noted in various terrestrial animals, the use of phytochemicals in fish farming has rarely been investigated. Fish culture is under pressure to decrease the use of synthetic antibiotics and chemotherapeutics because of the risk caused to humans by chemical residues in food and by antibiotic resistance being passed on to human pathogens. Consequently, efforts are being made to exploit plants, plant extracts or natural plant compounds as potential alternatives to synthetic chemicals for the stimulation of immune responses and disease resistance in fish. The phytochemicals contained in herbs may enhance the innate immune system and possess antimicrobial capabilities that may be of immense use in fish culture without causing any environmental and ⁄ or hazardous problems. Most phytochemicals are redox active molecules that have anti-oxidant characteristics that may improve the general physiological condition of fish. This review discusses the results emanating from different studies related to the in vivo application of plants and ⁄ or phytochemicals in fish in relation to immunostimulation, antipathogenic and antistress activities. Special emphasis is given to the use of Chinese and Indian herbs as immunostimulants in different finfish species during culture and as antibacterial agents against Aeromonas hydrophila.

There is a constant need to increase productivity in aquaculture, particularly to improve growth rate, feed utilization as well as stress resistance of fish. Because of consumer concerns and strict regulations in many countries, the use of synthetic chemicals, hormones and antibiotics is becoming unviable and natural compounds are more acceptable to the public. A wide variety of chemical compounds are found in plants, and many of them have been shown to have beneficial effects on appetite, growth and the immune status of fish acting through different mechanisms. Phytochemicals contained in herbs may enhance the innate immune system, possess antimicrobial capabilities, and are redox active molecules with antioxidant characteristics that may help to improve the general physiological condition of fish. Many studies have discussed the values of phytochemicals as feed additives. Another paramount concern related to phytochemicals is their endocrine modulator effect that can be applied both in aquaculture targeting the production of table fish and the growing sector of ornamental fish production. Different mechanisms such as the effects at the steroid receptor level, effects on steroid synthesis, distribution and excretion, actions on the hypothalamuspituitary-gonad axis, as well as indirect mechanisms including thyroid and growth hormone disruption have been postulated for the reproductive endocrine disruption in fish populations by phytochemicals. This paper reviews the results of a great number of studies focusing on phytochemicals such as essential oils, saponins, flavonoids and phytosterols discussing their effects on productive traits and the putative mechanism of action.

In this study the predation and ®sh prey selection of otters Lutra lutra L. living by eutrophic ®sh ponds on agricultural land and in a protected area of temperate climate in Hungary were investigated. The correlations between ®sh in the diet of the otters (by spraint analysis involved 1942 and 1280 samples for the two habitats) and the ®sh stock available (by harvest and sample ®shing) were generally close. Prey selection was signi®cantly related to selected species of a particular size range (P < 0.01). The preference calculations were performed with Ivlev's index of preference (E i , minimum 71, maximum +1). Regardless of species, the otters avoided (E i = 70.51) ®sh heavier than 1000 g, with a preference for individuals weighing between 500 and 1000 g (E i = 0.79). No substantial or clear preference was observed in the weight range below 500 g (E i = 70.02±0.38). The preference for ®sh in accordance with their characteristic sites of occurrence within the body of water was also signi®cant (P < 0.01). They avoided ®sh living primarily in open water (E i = 70.64) and to a lesser degree those occurring near the pond bed (E i = 70.22). They favoured ®sh inhabiting the area with a covering of aquatic plants (E i = 0.46), and showed a preference to a lesser degree for ®sh living in the shallow littoral regions (E i = 0.14). With the cessation of ®sh farming and the effect of the drastic changes which occurred in the vegetation, the otters fed substantially on the stock of alternative sources of prey such as amphibians and water insects as well as terrestrial animals, and at such times, depending on season, ®sh became a secondary source of prey.

No abstract

. 1999. Feeding habits and trophic niche overlap in a Carnivora community of Hungary. Acta Theriologica 44: 429-442.The seasonal feeding habits of the red fox Vulpes vulpes (Linnaeus, 1758), the stone marten Marłeś foina (Erxleben, 1777), the stoat Mustela erminea Linnaeus, 1758, the badger Meles meles (Linnaeus, 1758) and the otter Lutra lutra (Linnaeus, 1758) were studied in south-west Hungary, in the course of four years. The habitat conditions, because of human influences, were different in the first and second two years. Diet was examined by scat analysis (238, 262, 67, 50 and 1033 samples, respectively). Small mammals, mainly rodents, were the most important prey for foxes, stone martens and stoats in winter and spring. In summer and autumn insects and fruit were added to fox and marten diet, while birds were added to stoat diet. The badger's main food resources were invertebrates (mainly insects) and maize and, in autumn, rodents. Domestic animals (mainly poultry and rabbit) occurred in the diet of the foxes and martens in all seasons, carcasses (mainly Cervidae) in the diet of these predators and in that of the badgers. The predominant prey of otters was fish, but when the abundance of fish declined, the consumption of amphibians increased. Predation on game birds and hare was not significant. In all seasons, niche overlap was high between foxes, martens and stoats. Niche overlap between these species and the badger increased from spring to autumn. Niche overlap between terrestrial predators and the otter was low. The diet of predators were different between the 1st and 2nd periods.