Infection patterns of Nile tilapia (Oreochromis niloticus L.) by two helminth species with contrasting life styles

Abstract

The larval stages of Bolbophorus sp. (digenean) and Amirthalingamia macracantha (cestode) are frequently reported in Oreochromis niloticus in Uganda. Little, however, is known about their infection patterns. This study examined the influence of habitat type, host size, and sex and weather patterns on the parasite populations in Uganda. A total of 650 fish were collected between January and November 2008 from a reservoir, cages, fishponds and a stream. The prevalence and intensity of A. macracantha and the prevalence of Bolbophorus sp. differed across the water bodies reflecting the effect of habitat characteristics on parasite transmission. Host sex did not significantly influence the infection patterns, although female fish were slightly more parasitized than male and sexually undifferentiated individuals. The fish size was positively correlated with helminth infections demonstrating accumulation and prolonged exposure of larger (older) fish to the parasites. The metacercariae population did not vary significantly across months, while monthly A. macracantha infection fluctuated markedly. With regard to rain seasons, higher prevalence and intensity of A. macracantha were recorded in wet season. For Bolbophorus sp., only the prevalence varied with seasons, with higher prevalence recorded in the dry season than in wet season. Generally, Bolbophorus sp. responded weakly to changes in water body, host sex and size and weather patterns. Rainfall appears to be an essential cue for coracidia hatching.

Parasite communities of the elongate tigerfish Hydrocynus forskahlii (Cuvier 1819) and redbelly tilapia Tilapia zillii (Gervais 1848) from Lake Turkana, Kenya: influence of host sex and size

“…Nonetheless, the correlations of A. macracantha prevalence and mean intensities with T. zillii size (substrate spawner) were weak and contrasted with the study of Akoll et al (2012a), who found positive correlations with O. niloticus size (mouth brooder), probably reflecting host-specific differences. In contrast to our findings, other authors found no relationships between helminth abundance and fish size (Kadlec et al 2003;Ferrari-Hoeinghaus et al 2006;Morenikeji and Adepeju 2009;Madanire-Moyo et al 2010;Ibrahim 2012;Olurin et al 2012).…”

“…This co-occurrence raises new questions, particularly regarding the parasite`s unknown life cycle. Several authors (Aloo 2002;Florio et al 2009;Akoll et al 2012a;Otachi et al 2014) have reported A. macracantha plerocercoids encysted in the liver or intestinal wall of tilapias. To our knowledge, the only exception was in the original species description (Bray 1974), which did not explicitly mention whether the specimens were found encysted or free in the liver of T. nilotica from Sudan.…”

“…Its high prevalence and intensity can be explained by the possible ingestion of abundant intermediate hosts (possibly the copepod, Cyclops spp.) infected with procercoids (Aloo 2002;Akoll et al 2012a). Although the life cycle of A. macracantha has not been described (Bray 1974;Aloo 2002;Scholz et al 2004), those of the related gryporhynchid taxa involve planktonic copepods (e.g.…”

“…This means that H. forskahlii is maximally exposed to Contracaecum sp. 1 as juveniles inhabiting shallower waters, because, coincidentally, littoral zones exhibit high abundances of intermediate and definitive hosts (Akoll et al 2012a). This explains the high prevalence in smaller fish.…”

Why are the prevalence and diversity of helminths in the endemic Pyrenean brook newt Calotriton asper (Amphibia, Salamandridae) so low?

“…Host–parasite interactions may vary in accordance with ecological factors, habitat characteristics and phylogeny (Dobson, 2009; Lafferty, 2009; Akoll et al , 2011). An interesting question in parasitology is why some species or populations are more parasitized than others.…”