Diet overlap of non‐native common carp and native Nile tilapia: A potential cause for population reduction of Nile tilapia stock in Lake Ziway,Ethiopia

Lake Ziway harbours indigenous and exotic fish species including Nile tilapia (Oreochromis niloticus) and common carp (Cyprinus carpio). Nile tilapia was the dominant and preferred fish. However, its contribution to total catch has dramatically declined from 89.3% in 1994 to 27% in 2014 while the introduced common carp has increased from 0% before 2012 to 25% in 2014. Common carp potentially compete with Nile tilapia for available resources and could be a cause for the decline. Thus, the study explored the dietary overlap of the two species from April to August 2017. Schoener's overlap index (α) revealed significant dietary overlap between the two species (α = 0.84, between juveniles and α = 0.63, between adults). Juveniles fed mainly on animal origin (zooplankton and insects), while adult Nile tilapia have consumed plant origin (macrophyte and phytoplankton), and adult common carp fed on macrophytes and detritus. The presence of significant dietary overlap between the two species, particularly due to intense competition among juveniles, might cause the reduction of Nile tilapia stock because the native species has shown a competitive disadvantage for food in the presence of common carp. This study provides baseline information to researchers and decision makers working towards the sustainable resource utilisation of the system.     

Predation by Nile perch Lates niloticus (L.) on Oreochromis niloticus (L.), Cyprinus carpio (L.), Mugil sp. and its role in controlling tilapia recruitment in Egypt

Vulnerability of three fish groups (tilapia, common carp, mullet) to predation by Nile perch Lates niloticus was evaluated. The study was conducted in aquaria and in cages placed in concrete ponds. Common carp Cyprinus curpio was the more vulnerable to predation by Nile perch followed in order by mullet ( Mugil cephulus and M. cupito ) and Nile tilapia Oreochromis niloricus . Medium-size Nile perch (30–32 cm t.l. ) were able to consume tilapia up to 14 cm t.l. , while tilapia of 15 cm total length were not eaten. Ratios of 1 : 10 to 1 : 15 between Nile perch and ready-to-spawn females of O. niloticus were found to be adequate to control tilapia reproduction.     

Vigilance in Single- and Mixed-Species Groups of Tamarins (Saguinus labiatus and Saguinus fuscicollis)

By forming larger sizes of groups, individuals benefit from a decrease in vigilance, but the collective vigilance of the group as a whole is not compromised. We examined whether this group size effect is apparent in mixed-species groups of red-bellied tamarins (S. labiatus) and saddleback tamarins (S. fuscicollis) which form stable and permanent associations in the wild. We studied general vigilance and responses to hidden threatening stimuli in five captive groups of each species, while they were housed in single- and mixed-species groups. For vigilance, the individual rate was lower in the larger mixed-species groups than in the smaller single-species groups. In addition, the amount of time when at least one individual was vigilant was higher in mixed-species groups. This suggests that the tamarins alter their vigilance behavior in the presence of the other species. In response to hidden threats, both species performed brief vigilance checks and frequencies of checking did not differ in single- and mixed-species groups. However, both species had a significant reduction in the mean duration per check, and there was a reduced total amount of time spent vigilance checking in the mixed-species groups compared to the single-species groups, demonstrating the group size effect. Overall the mixed-species groups had a higher number and mean duration of checking than the smaller single-species groups. Given that the two species share a common set of predators, and respond to each other's alarm calls, these findings provide strong evidence that individuals of both tamarin species may be able to benefit from forming mixed-species groups via improved vigilance and monitoring of threats.     

The impacts of invasive Nile tilapia (Oreochromis niloticus) on the fisheries in the main rivers of Guangdong Province,China

Nile tilapia (Oreochromis niloticus) is one of the most widespread invasive fish species, and this species has successfully established populations in the major rivers of Guangdong Province, China. Field surveys and manipulative experiments were conducted to assess the impacts of Nile tilapia on fisheries. We determined that the increase of Nile tilapia in these rivers not only affects the CPUE (catch-per-unit-per-effort) of the fish community and native fish species but also reduces the income of fishermen. In the manipulative experiments, we observed that the growth of native mud carp decreased in the presence of Nile tilapia. Our results suggest that the invasion of Nile tilapia negatively affected the fishery economy and native fish species, and suitable control measurements should be taken.     

The interaction of innate and imposed colour perception: a behavioural approach

Nile tilapia were raised from eggs to 2 months of age under a coloured light regime (violet, blue, green, yellow, and red) and then tested for colour preference in a multiple chamber maze with different colour options. Fish were observed individually during three days at 8, 11, 14, and 17 h, every 2 min for 20 min and the visit frequency in each compartment was analyzed. Young Nile tilapia kept under yellow and red light showed preference for yellow and red, respectively. Fish held under violet, blue, and green light did not show any colour preference or avoidance. These results imply that environmental colour affects colour preference of Nile tilapia, possibly due to light-dependent shift of visual pigments in the retina, indicating that colour preference is not an innate response. This conclusion reinforces the idea that environmental colour modulates fish physiological and behavioural processes.     

Leaders of progressions in wild mixed-species troops of saddleback (Saguinus fuscicollis) and mustached tamarins (S. mystax), with emphasis on color vision and sex

Leadership of travel progression is an important aspect of group living. It is widely believed that trichromacy evolved to facilitate the detection and selection of fruit in the dappled light of a forest. Further, it has been proposed that in New World primate species, which typically contain a range of color vision phenotypes, at least one female in a group will be trichromatic (i.e., having three types of visual pigment, in contrast to the two types of pigment found in dichromatic individuals) and will lead the group to fruiting trees. We examine progression leadership within two wild mixed-species troops of saddleback (Saguinus fuscicollis) and mustached (Saguinus mystax) tamarins over a complete year. As whole units, the mixed-species troops were most frequently led by a mustached tamarin. This is the first time that mixed-species group leadership and individual leadership have been quantified in these tamarin species. In terms of single-species intragroup leadership, neither the visual status (dichromatic or trichromatic) nor the sex of individuals had a consistent effect across species. Saddleback tamarin groups were led by males more frequently than females, while evidence suggests that mustached tamarins may be female-led. The notion that all groups contain at least one trichromatic female that leads the troop to feeding trees was not supported.     

Feeding behavior and responsivity to food odors in Nile tilapia <Emphasis Type="Italic">Oreochromis niloticus</Emphasis> (Cichlidae) after chronic polisensory deprivation

The paper reports the study of the food searching behavior in the Nile tilapia Oreochromis niloticus before and after the experimental anosmia combined with visual deprivation. The threshold concentration of the water extract of the common food organisms (Chironomidae larvae) was found for the tilapia with intact olfaction to be 10^–4 g/L, which allows this fish to search for food under the restriction of visual reception. The food searching behavior in response to food odors is completely lost as a result of irreversible anosmia and do not be restored after a 4.5-month period even for the high concentrations of the extract (10^–1–10^–2 g/L). These findings point to the absence of external taste buds on the head, body, and fins, or to their extremely low numbers. It is assumed that tactile sense also plays a significant role in the food search and prey location in the Nile tilapia.     

Larval interspecific competition in two flea species parasitic on the same rodent host

Abstract.  1. The fleas Xenopsylla conformis and Xenopsylla ramesis exploit the same rodent host, Meriones crassus , and replace each other between two different habitats situated at the opposite sides of a steep precipitation gradient. It was hypothesised that the reason for this paratopic distribution is competition between larvae of the two species for food resources.
2. This hypothesis was tested by studying the performance of larvae of the two species in terms of their developmental success in mixed-species and single-species treatments under different air temperatures, relative humidities, substrate textures, and food abundance.
3. The number of individuals of X. conformis that survived until emergence depended significantly on the presence of competing species, being, in general, lower in mixed-species compared with single-species treatments. The decrease in developmental success of X. conformis in mixed-species treatments was found mainly during food shortage. In contrast, presence of the competitor did not affect the number of X. ramesis that survived until emergence. No effect of the presence of the competitor on duration of development or sex ratio was found in either species.
4. The results of this study, together with the results of our previous studies, provide an explanation for the paratopic distribution of X. conformis and X. ramesis that exploit the same host species.     

The ‘club’ cell and behavioural and physiological responses to chemical alarm cues in the Nile tilapia

The alarm response to skin extract has been well documented in fish. In response to skin extract, there is a decline in both locomotion activity and aggressive interactions. Our observation herein of these responses in the cichlid Nile tilapia, Oreochromis niloticus, confirmed the existence of the alarm response in this species. However, so far there has been a paucity of information on the autonomic correlates of this response. In this study, the ventilatory change in response to the chemical alarm cue was evaluated. This parameter was measured 4 min before and 4 min after exposure to 1 mL of either conspecific skin extract or distilled water (extract vehicle). Skin extract induced an increase in the ventilation rate, which suggested an anticipatory adjustment to potentially harmful stimuli. The chemical cue (alarm substance) also interfered with the prioritisation of responses to different environmental stimuli (stimuli filtering); this was suggested by the observation that the Nile tilapia declined to fight after exposure to a cue that indicates a risk of predation. Furthermore, histological analysis of the Nile tilapia skin revealed the presence of putative alarm substance-producing (club) cells.     

用RAPD技术对罗非鱼遗传变异的研究及应用(英文)

应用随机扩增多态性ＤＮＡ（ＲＡＰＤ）技术检测了一个奥利亚罗非鱼（ａｕ）和湘湖（ｎｘ）、美国（ｎｍ）、沙市（ｎｐ）三个尼罗罗非鱼养殖群体（Ｔａｂｌｅ１）。在２０个引物（Ｔａｂｌｅ ２）中筛选到１２个引物,它们的扩增产物显示了罗非鱼和尼罗罗非鱼二者在群体内或群体间存在遗传差异。其中（Ｆｉｇ．１）, ＯＰＺ０６、 ＯＰＺ１６、 ＯＰＺ１２和 ＯＰＺ１９四个引物分别有一个扩增片段具有种的特异性。它们的大小分别是９００、１５００、１７００和７３０ｂｐ。可以作为鉴别罗非鱼和尼罗罗非鱼二者的分子遗传标记。湘湖（ｎｘ）、美国（ｎｍ）和沙市（ｎｐ）三个尼罗罗非鱼群体内遗传变异相似性指数Ｓ分别为 ０．７９８、 ０．７９５和０．８２４（Ｔａｂｌｅ ３）。表明：这三个尼罗罗非鱼群体都保留了较高水平的遗传变异。而奥利亚罗非鱼（ａｕ）的群体内遗传变异最小。奥利亚罗非鱼（ａｕ）与湘湖（ｎｘ）、美国（ｕｍ）、沙市（ｕｐ）三个尼罗罗非鱼群体之间的遗传距离分别是０．２８５、０．２６２和０．３４４（Ｔａｂｌｅ ３）,说明奥利亚罗非鱼（ａｕ）和沙市尼罗罗非鱼（ｎｐ）杂交将可能产生较强的杂种优势。     

Biofilm development and enhanced stress resistance of a model,mixed-species community biofilm

Most studies of biofilm biology have taken a reductionist approach, where single-species biofilms have been extensively investigated. However, biofilms in nature mostly comprise multiple species, where interspecies interactions can shape the development, structure and function of these communities differently from biofilm populations. Hence, a reproducible mixed-species biofilm comprising Pseudomonas aeruginosa, Pseudomonas protegens and Klebsiella pneumoniae was adapted to study how interspecies interactions affect biofilm development, structure and stress responses. Each species was fluorescently tagged to determine its abundance and spatial localization within the biofilm. The mixed-species biofilm exhibited distinct structures that were not observed in comparable single-species biofilms. In addition, development of the mixed-species biofilm was delayed 1–2 days compared with the single-species biofilms. Composition and spatial organization of the mixed-species biofilm also changed along the flow cell channel, where nutrient conditions and growth rate of each species could have a part in community assembly. Intriguingly, the mixed-species biofilm was more resistant to the antimicrobials sodium dodecyl sulfate and tobramycin than the single-species biofilms. Crucially, such community level resilience was found to be a protection offered by the resistant species to the whole community rather than selection for the resistant species. In contrast, community-level resilience was not observed for mixed-species planktonic cultures. These findings suggest that community-level interactions, such as sharing of public goods, are unique to the structured biofilm community, where the members are closely associated with each other.     

Ecological niche modeling of the invasive potential of Nile tilapia Oreochromis niloticus in African river systems: concerns and implications for the conservation of indigenous congenerics

This study applied ecological niche models to determine the potential invasive range of Nile tilapia, Oreochromis niloticus, with a particular focus on river systems in southern Africa where it is now established and spreading. Computational tools such as niche models are useful in predicting the potential range of invasive species, but there are limitations to their application. In particular, models trained on native records may fail to predict the full extent of an invasion. This failure is often attributed to changes in either the niche of the invading species or the variables used to develop the models. In this study, we therefore evaluated the differences in the predictive power of models trained with different environmental variables, the effect of species range (native vs. introduced) on model performance and assessed whether or not there is evidence suggestive of a niche shift in Nile tilapia following its introduction. Niche models were constructed using Maxent and the degree of niche similarity was assessed using Schoener`s index. Null models were used to test for significance. Model performance and niche conservatism varied significantly with variable selection and species range. This indicates that the environmental conditions available to Nile tilapia in its native and introduced ranges are not congruent. Nile tilapia exhibited broad invasive potential over most of southern Africa that overlaps the natural range of endemic congenerics. Of particular concern are areas which are free of exotic species but are now vulnerable due to the promotion of fish introductions mainly for aquaculture and sport fishing.     

Spontaneous activity was unaffectedby ration size in Nile tilapia and gibel carp

Two growth trials using a range of ration sizes from starvation to maximum feeding suggested that linear relationships existed between specific growth rate and ration size for Nile tilapia and givel carp. Continuous measurement of activity showed that activity level, in terms of distance swum per day, was not affected significantly by ration size in both Nile tilapia and gibel carp.     

Effects of environmental colour on growth of Nile tilapia, Oreochromis niloticus (Linnaeus, 1758), maintained individually or in groups

Examined was the influence of different colours of light on the growth of adult Nile tilapia (Oreochromis niloticus) held either individually (initial size 12.8 ± 1.1 cm; 62.9 ± 15.6 g) or in groups (initial size 7.8 ± 0.8 cm; 17.2 ± 6.4 g). Various colours (blue 434.5 nm, violet 430.0 nm, red 609.7 nm, green 525.2 nm and yellow 545.2 nm) did not affect weight gain of fish held individually (initial to final weights: blue 62.5 ± 18.4 to 72.9 ± 16.0 g, violet 63.5 ± 17.8 to 78.0 ± 19.1 g, green 62.1 ± 13.0 to 72.9 ± 15.7 g, and yellow 60.4 ± 20.4 to 71.0 ± 21.1 g); red seemed to restrict growth (initial to final weights: 65.8 ± 13.3 to 71.8 ± 10.8 g). Final weight differences were observed among individuals in groups maintained under blue, violet, red and green light (smaller and larger fish: blue 13.2 ± 5.0 and 18.9 ± 7.0 g, violet 17.3 ± 5.2 and 23.8 ± 4.7 g, red 14.7 ± 3.3 and 23.9 ± 4.7 g, and green 19.4 ± 7.8 and 28.6 ± 8.1 g); however, under the yellow light there were no differences in final weights (smaller fish 19.1 ± 4.8 g; larger fish 26.2 ± 5.2 g). Under the red light, heterogeneity in growth was observed earlier than with the other colours. It is therefore suggested that the red colour might have some harmful effects on Nile tilapia growth, limiting weight gain when fish are individually maintained, and with weight differences increasing when fish are held in groups. On the other hand, the yellow light seems to be positive for Nile tilapia, as it appears not to affect individually‐held fish, but reduces variation in growth of group‐maintained fish, promoting growth homogeneity.     

The effect of rice-seeding rate and fish stocking on the floodwater ecology of the trench of a concurrent,direct-seeded rice-fish system

Concurrent rice-fish systems in the Mekong Delta, Vietnam, are characterized by a rice field surrounded by a trench (on average 1000 m², covering 15–20% of the field surface). Rice is direct seeded and fish are reared in polyculture. The most common species for polyculture are silver barb Barbodes gonionotus (Bleeker), common carp Cyprinus carpio L. and Nile tilapia Oreochromis niloticus (L.). In a 1996–1997 dry season experiment, the effects of (1) absence or presence of a fish polyculture, and (2) two different rice-seeding rates (100 and 300 kg pre-germinated rice per ha) on the trench floodwater ecology were studied. Fish were stocked in six out of twelve rice-fish plots at the Co Do experimental rice-fish station (10° 10 N and 105° 20 E). Silver barb, common carp and Nile tilapia were stocked in polyculture at densities of 3150, 310 and 550 fish/ha, respectively. Several hydrological and biological parameters of the trench floodwater were measured. About 65% of the observed variation in the trench floodwater could be attributed to the fishes stocked and changes in rice-seeding rate. The presence of a fish polyculture increased the water turbidity of the trench floodwater, mainly through suspension of mineral and organic material through fish perturbation. At the lower rice-seeding rate, this resulted in a lower primary production. Photosynthetic activity, dissolved oxygen am and pm showed significant decreases, but only at the lower rice-seeding rate in the presence of fish. Fish polyculture presence resulted in lower ortho-phosphate concentrations, higher phytoplankton communities and higher Protozoa numbers, most probably due to a higher availability of nutrients through fish defecation and perturbation. The rice-seeding rate had a significant impact on pH am, pH pm and temperature pm readings. The survival rate for Nile tilapia and the gross production for Nile tilapia and common carp was higher at the lower rice seeding rate, most probably due to a better aquatic environment of the field. In terms of fish production, the trench floodwater environment was better than the field floodwater. The trench is a very important part of the rice-fish system. It serves as a refuge and supplies reasonable amounts of phytoplankton and zooplankton to the fish.     

Associative learning and discrimination of motion cues in the harnessed honeybee Apis mellifera L.

We previously studied a conditioning paradigm to associate the proboscis extension reflex (PER) with monochromatic light (conditioned stimulus; CS) in harnessed honeybees. Here, we established a novel conditioning paradigm to associate the PER with a motion cue generated using graphics interchange format (GIF) animations with a speed of 12 mm/s speed and a frame rate of 25 Hz as the CS, which were projected onto a screen consisting of a translucent circular cone that largely covered the visual field of the harnessed bee using two liquid crystal projectors. The acquisition rate reached a plateau at approximately 40% after seven trials, indicating that the bees were successfully conditioned with the motion cue. We demonstrated four properties of the conditioning paradigm. First, the acquisition rate was enhanced by antennae deprivation, suggesting that sensory input from the antennae interferes with the visual associative learning. Second, bees conditioned with a backward-direction motion cue did not respond to the forward-direction, suggesting that bees can discriminate the two directions in this paradigm. Third, the bees can retain memory for motion cue direction for 48 h. Finally, the acquisition rate did not differ significantly between foragers and nurse bees. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

尼罗罗非鱼早期发育形态及其在珠江水系的空间分布

【背景】罗非鱼作为联合国粮农组织（FAO）向全世界推广养殖的优良品种之一,有多个品系,其养殖范围已遍布85个国家和地区。1956年我国从越南引进莫桑比克罗非鱼,经过养殖及推广,2006年我国罗非鱼产量达到100万t。但是,该外来物种在给我国带来良好经济价值的同时,对土著种类及水环境造成了极大的影响。【方法】对近几年珠江水系渔获物的调查数据进行整理,并观察尼罗罗非鱼早期发育形态,统计尼罗罗非鱼苗对其他鱼苗的最大捕食量及捕食规格,以分析罗非鱼生物学特性及其在珠江水系的入侵现状。【结果】尼罗罗非鱼早期发育快,卵黄营养非常丰富,比珠江水系土著种类更有竞争性;罗非鱼苗呈现很强的攻击性与捕食性;尼罗罗非鱼已经扩散到珠江水系各主要河流,并在部分江段形成优势种群。【结论与意义】尼罗罗非鱼种群快速扩张,对土著种已构成严重威胁,有必要将其列为珠江水系高危入侵种。     

Changes in the flocking behaviour of wintering English titmice with time,weather and supplementary food

Over the course of one winter, the food supply of birds living in a deciduous woodland in southern England was supplemented and unsupplemented during alternating periods. In the presence of substantial predation pressure from hawks, the sociality of blue tits, Parus caeruleus, and great tits, P. major, showed significant partial correlations with several weather and temporal factors when the woodland was unsupplemented. Such correlations between social behaviour and abiotic factors diminished significantly when the birds had access to extra food. Blue tits and great tits without access to supplemental food flocked significantly more often with other species while foraging than when they were food-supplemented. Long-tailed tits, Aegithalos caudatus, ignored the artificial food and foraged in mixed-species flocks to the same extent in both unsupplemented and food-supplemented periods. Results disprove the hypothesis that mixed-species foraging groups are caused by increased predation protection alone, and they support the hypotheses that mixed-species foraging groups are caused by increased foraging efficiency alone or by a combination of increased foraging efficiency and increased protection from predators.     

The influence of flocking on the foraging behaviour of the chough (Pyrrhocorax pyrrhocorax) and the Alpine chough (P. graculus) coexisting in the Alps

We studied the flocking and foraging behaviour of the chough Pyrrhocorax pyrrhocorax and the Alpine chough P. gruculus coexisting in the south-western Italian Alps in order to evaluate the costs and benefits of foraging in single- and mixed-species flocks.
In the single-species context, flock size significantly affected the foraging behaviour of the Alpine chough; in larger flocks, the birds stayed for a shorter time in a patch and fed more quickly than in smaller flocks. Flock size did not significantly affect the foraging behaviour of the chough, probably because of the small number of individuals per flock.
The propensity for mixed-species flocking was rather low. The observed frequencies of single-species flocks of choughs and Alpine choughs were significantly higher than those expected on the basis of random flocking, whereas the observed frequencies of mixed-species flocks of the two species were lower than those expected. The stay times became significantly shorter for the chough in the presence of the Alpine chough. Moreover, feeding rates of the Alpine chough were significantly lower in the presence of the dominant chough.
The present study does not confirm the hypothetical foraging advantages of flocking. In single-species flocks, the benefits for the Alpine chough (higher feeding rates in larger flocks) were roughly compensated by the costs (shorter stay times in larger flocks), whereas the chough apparently neither gained benefits nor endured costs.
In mixed-species flocks, the Alpine chough sustained costs due to a reduction of feeding rates and the chough suffered costs due to a reduction of stay times. Hence, on average, single-species flocking gives no evident foraging advantages to either the chough or the Alpine chough, whereas mixed-species flocking provides some disadvantages for both species.