Length–length and length–weight relationships for four endemic Cyprinid species in Küçük Menderes River Basin,Turkey

Length–length and length–weight relationships were studied for four endemic Cyprinid species from the Küçük Menderes River Basin located in the Western Anatolian region of Turkey. Fish were sampled from Tahtal? and Beyda?? reservoirs, Bulgurca, ?a?al and Azmak streams during 2013–2014, using multimesh gillnets in the reservoirs and by electrofishing in the streams. First records of length–weight relationships for Barbus pergamonensis Karaman, 1971, Squalius kosswigi (Karaman, 1972) and Petroleuciscus smyrnaeus (Boulenger, 1896) are reported in addition to three new maximum total lengths for Chondrostoma holmwoodii (Boulenger, 1896), Squalius kosswigi (Karaman, 1972) and Petroleuciscus smyrnaeus (Boulenger, 1896).     

GnRH-systems in the forebrain of cichlid fish.

The neuronal systems that contain gonadotropin-releasing hormone (GnRH) were quantitatively examined in the forebrain of two cichlid species (Oreochromis niloticus Lin. and Tilapia maria Boulenger) using tracing methods and immunostaining. In both species the nucleus olfacto-retinalis and a population of neurons in the basal preoptic region contained GnRH. The nucleus olfacto-retinalis was divided into several neuronal subpopulations which differed with respect to cytology, projection pattern, and peptide content. GnRH cell number increased with body size, the rates being different for the different subpopulations. A sexual dimorphism was found in the basal preoptic region of Tilapia; males had significantly fewer GnRH-containing cells than females. Selective staining of the basal preoptic region demonstrated that this cell group is the main source of GnRH-innervation of the pituitary gland and indicate that the molecular forms of GnRH expressed in the two cell populations studied may be different.     

The food and feeding habits of Tilapia species in the Lagos Lagoon

The food of Tilapia mariae (Boulenger), Tilapia guineensis * (Bleeker) and Tilapia melano-theron melanotheron * (Rupell) were investigated. It is shown that T. guineensis and T. m. melanotheron which were the more abundant species had similar food habits. The intensity of feeding of both species and the possible competition for food between them are discussed.     

A Redescription of the Tropical Brazilian Serpent Apostolepis Nigrolineata (Peters 1869), (Colubridae: Elapomorphinae), Synonymous With A. pymi Boulenger 1903

The re-examination of the holotypes of both Apostolepis nigrolineata (Peters 1869) and Apostolepis pymi Boulenger 1903 revealed the former as the juvenile stage of the latter. According to priority, A. pymi is rendered void, and this later given name is hereby declared invalid. The synonymy is confirmed by data of a publication on agedependent variation in size, coloration and scalation, based on recently collected specimens. These characters also allow a clear discrimination of the closely related A. quinquelineata Boulenger 1896.     

The importance of the littoral epiphyton as food for commercial fish in the recent African man-made lake, Nyumba ya Mungu reservoir, Tanzania

Nyumba ya Mungu reservoir is a man-made lake in the Kilimanjaro region of northern Tanzania. The commercial fisheries are principally based on the cichlids, Sarotherodon pangani Lowe, S. jipe Lowe, S. esculentus Graham, and Tilapia rendalli Boulenger.
Examination of gut contents revealed that the dominant species, S. pangani and S. jipe , fed on the epiphyton attached to the vegetation in the littoral zone, S. esculentus was a phytoplankton filter feeder, and T. rendalli consumed macrophytes and associated epiphytes.
A fish exclosure quantitatively demonstrated that the epiphyton community was appreciably depleted by the grazing of fish. After 35 days the mean epiphyton density on the submerged surfaces of Cyperus articulatus L. within the exclosure was 285 times 10³ individuals cm^-2 shoot, but only 181 times 10³ individuals cm^-2 shoot on grazed surfaces outside the exclosure. The differences were statistically significant, and corresponded to a difference in biomass of about 6.5 g organic dry weight m^-2 lake surface. Vertical profiles of periphyton density on Cyperus indicated that fish grazed mainly below a depth of 100 mm from the water surface.
The littoral epiphyton → commercial fish food chain, which may be unique, is considered to predominate in Nyumba ya Mungu, and is compared with the major food chains of commercial fish in some other African natural and man-made lakes.     

Mercury in tigerfish (Hydrocynus vittatus, Castelnau), green happy (Sargochromis codringtonii, Boulenger) and kapenta (Limnothrissa miodon, Boulenger) from Lake Kariba, Zimbabwe

Concentrations of total mercury were determined in Hydrocynus vittatus (Castelnau), Sargochromis codringtonii (Boulenger), and Limnothrissa miodon (Boulenger) from two localities in Lake Kariba, Zimbabwe.
The mean concentrations of total mercury in H. vittatus from Basin 5 and Basin 2 were 0.08 mg kg⁻¹ and 0.094 mg kg⁻¹, respectively. In S. codringtonii, mean concentrations were 0.004 mg kg⁻¹ and 0.026 mg kg⁻¹ for Basins 5 and 2, respectively. No mercury was detected in L. miodon from Basin 2 while samples from Basin 5 had a mean concentration of 0.069 mg kg⁻¹ (wet weight). Total mercury concentrations were also determined on a dry weight basis.
Within each sampling area, total mercury concentrations were significantly different among species ( P  < 0.05). For H. vittatus and S. codringtonii, total mercury concentrations (in the same species) were not significantly different between the two localities ( P  < 0.05).
The factors causing the observed differences in total mercury between similar species from different localities and among different species in the same locality (sampling area) are discussed. From the observed low levels of mercury in all three species, it was concluded that the mercury constituted 'background levels'. These levels are below the maximum concentrations permissible in human fish foods.     

Preference of Tilapia rendalli (Boulenger) for some species of aquatic plants

Preference of juvenile red-breasted bream, Tilapia rendalli (Boulenger), for the macrophytes Ceratophyllum demersum L., Lagarosiphon ilicifolius (Oberm), Najas pectinata (Magnus) and Valisneria aethiopica (Frenzl) was determined. Fish were offered a mixture of the four macrophytes in equal quantities to determine selection. Preference was shown for V. aethiopica , whilst C. demersum was least selected. This preference order was checked by examination of stomach contents of fish from the same population in the wild and the differences are discussed.     

Phytoplankton chytridiomycosis: community structure and infectivity of fungal parasites in aquatic ecosystems

Fungal parasitism is recurrent in plankton communities, especially in the form of parasitic chytrids. However, few attempts have been made to study the community structure and activity of parasites at the natural community level. To analyse the dynamics of zoosporic fungal parasites (i.e. chytrids) of phytoplankton, samples were collected from February to December 2007 in two freshwater lakes. Infective chytrids were omnipresent in lakes, with higher diversity of parasites and infected phytoplankton than in previous studies. The abundance and biomass of parasites were significantly higher in the productive Lake Aydat than in the oligomesotrophic Lake Pavin, while the infection prevalence in both lakes were similar and averaged about 20%. The host species composition and their size appeared as critical for chytrid infectivity, the larger hosts being more vulnerable, including pennate diatoms and desmids in both lakes. The highest prevalence (98%) was noted for the autumn bloom of the cyanobacterium Anabaena flosaquae facing the parasite Rhizosiphon crassum in Lake Aydat. Because parasites killed their hosts, this implies that cyanobacterial blooms, and other large size inedible phytoplankton blooms as well, may not totally represent trophic bottlenecks because their zoosporic parasites can release dissolved substrates for microbial processes through host destruction, and provide energetic particles as zoospores for grazers. Overall, we conclude that the parasitism by zoosporic fungi represents an important ecological driving force in the food web dynamics of aquatic ecosystems, and infer general empirical models on chytrid seasonality and trophodynamics in lakes.     

Ecological studies on crater lakes in West Cameroon Zooplankton of Barombi Mbo, Mboandong, Lake Kotto and Lake Soden

The zooplankton of four crater lakes in North-west Cameroon has been studied by means of vertical hauls from the bottom to the surface. Two of the lakes are deep, with sparse phytoplankton, while the other two are shallow with dense blooms of blue-green algae. All the lakes are without planktonic Cladocera. In Lake Kotto, Mboandong and Barombi Mbo the dominant zooplankter is Mesocyclops (Thermocyclops) hyalinus , which is replaced in Lake Soden by Mesocyclops leuckarti. Larvae of Chaoborus are present in all the lakes. In the two deep lakes, Soden and Barombi Mbo, the dominant rotifer is Polyarthra dolichoptera , but in the two shallow lakes, Kotto and Mboandong, three species, Hexarthra mira, Brachionus fakatus and B. caudatus , make up the bulk of the rotifers.
In Barombi Mbo during the daytime most of the zooplankton was in the top 20 m, but most of the Chaoborus larvae were below 20m.
The standing crops of zooplankton in these lakes are low compared with those of lakes in the Kigezi District of Uganda.
The most remarkable feature of the zooplankton in these lakes is the occurrence of dwarfed forms. Both species of cyclopoid copepods and the eight identifiable species of Rotifera are smaller here than in most other localities. Factors which may be associated with this dwarfing are low latitude with constant high temperature, low phytoplankton availability, and the low ratio of drainage area to lake area.     

Food borne parasites as indicators of trophic segregation between Arctic charr and brown trout

The habitat and diet choice and the infection (prevalence and abundance) of trophically transmitted parasites were compared in Arctic charr and brown trout living sympatrically in two lakes in northern Norway. Arctic charr were found in all main lake habitats, whereas the brown trout were almost exclusively found in the littoral zone. In both lakes the parasite fauna reflected the niche segregation between trout and charr. Surface insects were most common in the diet of trout, but transmit few parasites, and accordingly the brown trout had a relatively low diversity and abundance of parasites. Parasites transmitted by benthic prey such as Gammarus and insect larva, were common in both salmonid host species. Copepod transmitted parasites were much more common in Arctic charr, as brown trout did not include zooplankton in their diets. Parasite species that may use small fish as transport hosts, were far more abundant in piscivorous fish, especially brown trout. The seasonal dynamics in parasite infection were also consistent with the developments in the diet throughout the year. The study demonstrates that the structure of parasite communities of charr and the trout is highly dependent on shifts in habitat and diet of their hosts both on an annual base and through the ontogeny, in addition to the observed niche segregation between the two salmonid species.     

The food of a community of East African freshwater fishes

Quantitative data on the food of the fishes inhabiting Lake Mcllwaine, Rhodesia, show that the feeding of the dominant species in this community ( Clarias gariepinus (Burchell), Hydrocynus vittatus (Castelnau), Tilapia melanopleura Dumeril, Tilapia mossamhica Peters, Tilapia macrochir Boulenger, Labeo altivelis Peters, and Gnathonemus macrolepidotus (Peters)) covers a wide spectrum, and almost all elements of the potential food supply are utilized. Exceptions are noted, however, and the introduction of the Indian carp, Catla catla (Cuv. & Val.), is advocated in order to utilize the large blooms of phyto- and zooplankton. The oligochaete, Branchiura cf. sowerbyi , which forms over 50% of the benthic biomass is also not utilized as a source of fish food. However, no fish species is known to feed on oligochaetes to any large extent. Predation by the Tigerfish, Hydrocynus vittatus , is shown to have severe effects upon recruitment to the valuable Tilapia fishery, and the reduction of the abundance of H. vittatus by means of selective fishing techniques is advocated.     

The food of a community of East African freshwater fishes

Quantitative data on the food of the fishes inhabiting Lake Mcllwaine, Rhodesia, show that the feeding of the dominant species in this community ( Clarias gariepinus (Burchell), Hydrocynus vittatus (Castelnau), Tilapia melanopleura Dumeril, Tilapia mossamhica Peters, Tilapia macrochir Boulenger, Labeo altivelis Peters, and Gnathonemus macrolepidotus (Peters)) covers a wide spectrum, and almost all elements of the potential food supplyare utilized. Exceptions are noted, however, and the introduction of the Indian carp, Catla catla (Cuv. & Val.), is advocated in order to utilize the large blooms of phyto- and zooplankton. The oligochaete, Branchiura cf. sowerbyi , which forms over 50% of the benthic biomass is also not utilized as a source of fish food. However, no fish species is known tofeed on oligochaetes to any large extent. Predation by the Tigerfish, Hydrocynus vittatus , is shown to have severe effects upon recruitment to the valuable Tilapia fishery, and the reduction of the abundance of H. vittatus by means of selective fishing techniques is advocated.     

Parasites and parallel divergence of the number of individual MHC alleles between sympatric three‐spined stickleback Gasterosteus aculeatus morphs in Iceland

Two pairs of sympatric three‐spined stickleback Gasterosteus aculeatus morphs and two single morph populations inhabiting mud and lava or rocky benthic habitats in four Icelandic lakes were screened for parasites and genotyped for MHC class IIB diversity. Parasitic infection differed consistently between G. aculeatus from different benthic habitats. Gasterosteus aculeatus from the lava or rocky habitats were more heavily infected in all lakes. A parallel pattern was also found in individual MHC allelic variation with lava G. aculeatus morphs exhibiting lower levels of variation than the mud morphs. Evidence for selective divergence in MHC allele number is ambiguous but supported by two findings in addition to the parallel pattern observed. MHC allele diversity was not consistent with diversity reported at neutral markers (microsatellites) and in Þingvallavatn the most common number of alleles in each morph was associated with lower infection levels. In the Þingvallavatn lava morph, lower infection levels by the two most common parasites, Schistocephalus solidus and Diplostomum baeri, were associated with different MHC allele numbers.     

Occurrence of myxosporean parasites in the gills of two tilapia species from Lake Nokoué (Bénin, West Africa): effect of host size and sex, and seasonal patterns of infection

The gill myxosporean parasites of 2 euryhaline tilapias from Lake Nokoué, Sarotherodon melanotheron melanotheron (Rüppel, 1853) and Tilapia zillii (Gervais, 1852), were investigated from October 1987 to October 1989. A total of 391 S. m. melanotheron and 222 T. zillii were examined. Both of the fish species studied were infected by 3 host-specific myxosporean parasites for which prevalence greatly varied during our investigations. The 2 most common ones were Myxobolus sp. and M. zillii, which were located in the branchial filament. No significant fish sex effect was found for these 6 different myxosporean parasites. As seasonal pattern was clearly demonstrated for M. zillii while a host size effect was found for M. dossoui. However, further investigations of these myxosporean infections are necessary to determine the real effect of these parasites on their host, as host fecundity and survival was not assessed.     

BEHAVIOUR OF A RADIO-TAGGED TILAPIA RENDALLI BOULENGER IN LAKE NGEZI,ZIMBABWE

SUMMARY

The behaviour of a single specimen of Tilapia rendalli Boulenger was observed June through October 1986 in Lake Ngezi, Zimbabwe, by the use of a surgically-implanted radiotransmitter. The individual displayed a distinct homing response on two occasions, returning to the cove of capture (1) 1.5 km away within 48 hours of release (95Z of the distance was covered in 24 hours), and (2) after a lengthy migration some 6.0 km up the lake with other tilapia. During the only observed migration in late June, the fish travelled a conservative distance of 6.7 km over a 5-day period, sometimes at rates > 150 m/hr. The fish was also characterized by strong territoriality (i.e., preference to the cove of capture) and avoidance to the approach of the researcher by boat.     

Fish condition in introduced tilapias of Ugandan crater lakes in relation to deforestation and fishing pressure

This study identifies environmental predictors of the condition of two introduced tilapia species (Oreochromis leucostictus and Tilapia zillii) that are known to have divergent trophic niches (planktivore and herbivore, respectively) in 17 crater lakes in western Uganda. We asked whether fish condition differs among lakes characterized by differences in fishing pressure and catchment deforestation; and we related relative condition factor to gradients of environmental variation across lakes. Lakes characterized by severe catchment deforestation tended to be lakes with high fishing pressure, so it was difficult to explore independent and interactive effects. However, mean relative condition factor was higher in populations with high fishing pressure compared to populations with low fishing pressure for both O. leucostictus and T. zillii. The condition of O. leucostictus populations was higher in lakes with severely deforested catchments; but mean relative condition factor of T. zillii did not differ between deforestation categories. Principal components analysis (PCA) was used to describe the major environmental gradients of variation among the lakes; and PCA factor scores were regressed against relative fish condition. The association between fish condition and environmental gradients was stronger for O. leucostictus than for T. zillii. For O. leucostictus, fish condition was related to PC1 (43% of the variance) and factors that loaded most heavily included Chl-a, water transparency, lake area and depth, suggesting higher condition in lakes characterized by higher primary productivity and smaller size. For T. zillii, PC3 (11%) was the only axis related to fish condition; and factors that loaded most heavily included lake area (positive), and conductivity and total nitrogen (negative). Some of the larger lakes are characterized by higher availability of macrophytes that may positively affect the food base for T. zillii.     

Dactylogyrids on the gills of roach in central Finland: features of infection and species composition.

Monogenean parasites were examined from the gills of 660 roach (Rutilus rutilus) in four interconnected lakes in Central Finland between February and November 1986 and in three of the same lakes between February and December 1988. One of the lakes is eutrophic and polluted due to a paper and pulp mill, one is oligotrophic and in a natural state, and the other two lakes are eutrophic. The prevalence of Dactylogyrus infection was always high. Differences between the lakes and the years were observed in the intensity of infection, which was significantly higher in the polluted lake. The intensity was also higher in older fish. Nine Dactylogyrus species were found, and of these D. crucifer and D. nanus were numerically dominant in all of the lakes studied, especially in the oligotrophic lake. In 1986 D. fallax, D. similis and D. suecicus constituted significant proportions of the fauna in the polluted lake. D. micracanthus was most common in the eutrophic lakes. In 1988 the species composition in the polluted lake was most similar to that in the eutrophic lake.     

An experiment on the culture of Tilapia esculenta (Graham) and Tilapia zillii (Gervais) (Cichlidae) in fish ponds

Segregated populations of Tilapia zillii and Tilapia esculenta were kept in artificial ponds. Supplementary food was given and phytoplankton was encouraged by the addition of superphosphate and ammonium sulphate fertilisers. The fry were cropped regularly in an attempt to control population size. A control population of T. zillii was also established in which none of these procedures were carried out.
The growth of T. esculenta was found to be dependent upon the phytoplankton density of the pond whilst T. zillii successfully utilized the supplementary food and grew well. The T. esculenta population also produced more fry than the T. zillii population. The comparative advantages of planktrvorous/brooders and herbivorous/guarders in fish culture are considered.
Despite the fecundity of the species used a population of known composition was maintained by manual cropping of the fry.
The addition of ammonium sulphate to the ponds caused blooms of phytoplankton which in turn had effects upon the base reserves and pH of the water, and probably caused some reduction of oxygen concentration beneath surface scums. This last point is used to explain the changes in phosphate and calcium content of the water also observed.
The low oxygen concentration frequently noted in the mornings probably affected the feeding behaviour of the fishes, and was low enough to have affected metabolism directly.     

Zooplankton associations in Zimbabwe

The specific composition and diversity of the zooplankton in 18 impoundments in Zimbabwe were analysed on the basis of samples taken in July and August 1983. All the lakes lay at altitudes over 1200 m, with the highest at 2270 m.
Thirty species of Rotifera and 20 species of Crustacea were identified, but the mean numbers of species per lake were 5·7 rotifers and 4·5 crustaceans. Some records represent considerable extensions of known ranges. Daphnia laevis was the most widespread and frequently dominant crustacean, while among the rotifers Keratella cochlearis was most frequently dominant, particularly in the lakes at the upper part of the altitudinal range.
Ordination and cluster analysis of the associations revealed a group of lakes with closely interrelated similarities which could be attributed to their lying on tributaries of the same river system and receiving trout from the same hatchery. These analyses also picked out the lowest locality as the most divergent and the one showing the most typically tropical zooplankton association. Although all the lakes were well within the tropics, their altitudes seem to have excluded some of the widespread tropical African zooplankters.
The possibility that these associations could be formed by random colonization is discussed and dismissed.
The momentary species composition of these Zimbabwean zooplankton associations was similar to that given by Pennak (1957) for the world average, although the mean number of species of Copepoda was significantly lower than the world average. Comparisons with data from Brazil and Lake Maggiore indicate the need for a further geographical analysis.
A comparative study of the species diversity in impoundments of different sizes indicates that, over several orders of magnitude of area, the number of species of Ciadocera and Copepoda shows a small increase, but the number of species of Rotifera shows a much larger and more variable increase.