Spatial and Temporal Variation of Cestode Infection and its Effects on Two Small Barbs (Barbus humilis and B. tanapelagius) in Lake Tana, Ethiopia

Abstract

Pseudophyllidean cestodes as Ligula have a complex life cycle with cyclopoid copepods as first intermediate host, zooplanktivorous fish as second, and piscivorous birds as final host. We studied the effects of diet, season and habitat occupation on the prevalence of plerocercoid larvae of the tapeworm Ligula intestinalis in two closely related small barbs and the effects of the parasites on the barbs life histories in Lake Tana (Ethiopia) during 1 year. In all affected barbs L. intestinalis caused retardation in gonad development, maturation at reduced size and lower absolute fecundity. Infection rate, averaged over all habitats was significantly higher in B. tanapelagius (10%) than in B. humilis (6%). Below a threshold of 48 mm the infection rate was zero for both barbs, this coincided with a very low proportion of copepods in their diets, increasing up to 90 and 55%, respectively, for their largest size class (81-90 mm). The relatively high infection rate in B. tanapelagius is explained by its obligatory zooplanktivorous feeding behaviour, ingesting a relatively high proportion of infected cyclopoid copepods. This is in contrast with B. humilis, which is a polyphagous species, feeding both on zooplankton and benthic invertebrates. Significant seasonal effects in infection rates were observed. In both barb species infection rates were lower during the breeding season. Only for B. tanapelagius a significant negative correlation was observed between rain fall and infection rate, probably caused by an increased turbidity that decreases feeding efficiency on zooplankton. Habitat type had also a significant effect on infection rate. Barbus humilis showed a much higher infection rate in shallow clear water (10%) than in shallow turbid water (3%), whereas B. tanapelagius showed much higher infection rates in the shallow sublittoral (13%) than in the deeper pelagic (7%). Most likely, birds predate more efficiently on barbs in shallow clear waters than in shallow turbid and deep waters.

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

“…6b). Our results are, however, contrary to findings of Dejen et al (2006). These authors observed a decline in Ligula intestinalis infection and attributed this to a reduced uptake of plankton because of high turbidity.…”

“…The host length was significantly correlated with A. macracantha and not with Bolbophorus sp. As reported in various studies from other species, larger fish harboured more endohelminths than smaller ones (Bell and Burt 1991;Poulin 1999;González and Acuña 2000;Fellis and Esch 2004;Dejen et al 2006). The positive correlation is explained by parasite accumulation in larger fish due to prolonged exposure and ontogenetic habitat and feeding shifts (Esch and Fernändez 1993;Paperna 1996;Marcogliese 2002).…”

“…In space, helminths infection levels are linked to differences in the physicochemical characteristics of the water bodies (Hartvigsen and Halvorsen 1994;Ondrackova et al 2004a). Habitat characteristics, such as waterbed morphology and type, gradient of the banks, the surrounding vegetation cover and the size of the water body, influence the establishment and interaction between hosts and, consequently, the transmission and proliferation of parasites (Ondrackova et al 2004a;Dejen et al 2006). The creation of artificial water bodies such as ponds and reservoirs may create favourable habitats that promote parasite proliferation (Lafferty and Kuris, 1999;Morley 2007).…”

“…Some studies found no seasonality in parasite populations (Aloo 2002;Vincent and Font 2003). Other studies reported apparent seasonal variations in parasite abundance associated with rainfall (Steinauer and Font 2003;Jiménez-García and VidalMartínez 2005;Dejen et al 2006). Such inconsistent information hampers developing sustainable disease management plans for aquaculture systems.…”

THE OCCURRENCE OF Ligula intestinalis IN ITS FISH HOST Rutilus rutilus (L.) AND THE EFFECTS OF PARASITE ON THE FISH GROWTH (BÜYÜKÇEKMECE RESERVOIR, TURKEY)

“…Also, many researchers have studied some effects of this parasite for fish host such as growth, endocrine system, gonadal development and had determined that L. intestinalis was caused many pathogenic effect on host fish. The parasite can cause damage to the host fish specimens especially by compression and atrophy of vital organs including the gonads, liver in the coelomic cavity of the infected fish (Öztürk and Altınel, 2001;Jopling and Taylor, 2003;Oğuz et al, 2004;Carter et al, 2005;Hecker and Karbe, 2005;Dejen et al, 2006). Similarly, in present study, macroscopic investigations showed that stomachs of fish specimens were swollen and gonads were deformed.…”