First maxillae suction discs in Branchiura (Crustacea): development and evolution in light of the first molecular phylogeny of Branchiura, Pentastomida, and other "Maxillopoda"

The fish ectoparasites Branchiura (Crustacea) display two different ways of attachment to the fish surface as adults: the first maxillae are either hooks (Dolops) or suction discs (Argulus, Chonopeltis, and Dipteropeltis). In larval Argulus foliaceus the first maxillae are hooks. With the first molecular phylogeny of the Branchiura as a background, the present paper discusses the evolutionary scenarios leading to hooks versus suction discs. Specific homologies exist between larval Argulus foliaceus hooks and adult Dolops ranarum hooks. These include the presence of a comparable number of segments/portions and a distal segment terminating in a double structure: a distal two-part hook (in Argulus) or one hook and an associate spine-like structure (in Dolops). In the phylogenetic reconstruction based on three molecular markers (mitochondrial 16S rRNA, nuclear 18S and 28S rRNA), Dolops ranarum is found to be in a sister group position to all other Branchiura, which in this analysis include six Argulus and one Chonopeltis sequences. Based on the molecular phylogeny a likely evolutionary scenario is that the ancestral branchiuran used hooks (on the first maxilla) for attachment, as seen in Dolops, of which the proximal part was subsequently modified into suction discs in Argulus and Chonopeltis (and Dipteropeltis). The sister group relationship of the Branchiura and Pentastomida is confirmed based on the most comprehensive taxon sampling until now. No evidence was found for a branchiuran in-group position of the Pentastomida.     

Determinants of the parasite community of clariid fishes from Lake Victoria, Tanzania

The factors that determine parasite assemblages among the clariid fishes of Lake Victoria, Tanzania were studied between August 2003 and February 2005. Six hundred and fifty-six fish belonging to seven species were necropsied and examined for parasites, from which 31 species of metazoan parasites were recorded. The community was dominated by the nematodes both in species and numbers. Most species were generalists with only two trematodes, Diplostomum mashonense and Tylodelphys species, being specialists of Clarias gariepinus. Ten species were considered core and predictable. Parasite species richness, number of individuals per host and Shannon-Wiener diversity indices were generally high. At the compound community level, a mean number of 7.8 parasites were shared among different species of fish and the maximum number of parasites species per fish at the infracommunity level was seven. Levels of similarity in parasite species richness at the component community level ranged from 29.6 to 61.5%. The study concludes that parasite communities in clariid fishes of Lake Victoria are structured by ecological factors. At the infracommunity level, host size, diet and vagility promoted a richer parasite community. At the compound level, two factors were crucial, namely the intermixing of the waters in the lake and the predominant and mobile C. gariepinus.     

Mucosal response in African catfish after administration of Vibrio anguillarum O2 antigens via different routes

The aim of this study was to investigate the possibility of mucosal vaccination in African catfish (Clarias gariepinus) with Vibrio anguillarum O2 bacterins. The antigen was administered via different routes: anal intubation, oral administration, intraperitoneal injection and immersion. To monitor the antigen uptake, a competitive ELISA was used. The antibody response was measured using an indirect ELISA. Increased antibody levels were found in bile and mucus upon anal intubation, which was not the case after intraperitoneal injection. The data indicate that oral vaccination of fish may be possible when antigens can reach the second gut segment in sufficient quantities and in the right form as confirmed by the recorded substantial induction of systemic and mucosal immunity. The results obtained are a strong indication for mucosal immune response and the two compartmental models for immune response in fish.     

The African sharptooth catfish Clarias gariepinus can tolerate high levels of ammonia in its tissues and organs during four days of aerial exposure

The African sharptooth catfish Clarias gariepinus lives in freshwater, is an obligatory air breather, and can survive on land during drought. The objective of this study was to elucidate how C. gariepinus defends against ammonia toxicity when exposed to terrestrial conditions. During 4 d of aerial exposure, there was no accumulation of urea in its tissues, and the rate of urea excretion remained low. Thus, exposure to terrestrial conditions for 4 d did not induce ureogenesis or ureotely in C. gariepinus. Volatilization of NH(3) was not involved in excreting ammonia during aerial exposure. In addition, there were no changes in levels of alanine in the muscle, liver, and plasma of C. gariepinus; nor were there any changes in the glutamine levels in these tissues. However, there were extraordinarily high levels of ammonia in the muscle (14 micromol g(-1)), liver (18 micromol g(-1)), and brain (11 micromol g(-1)) of fish exposed to terrestrial conditions for 4 d. This is the first report on a fish adopting high tolerance of ammonia in cells and tissues as the single major strategy to defend against ammonia toxicity during aerial exposure. At present, it is uncertain how C. gariepinus tolerates such high levels of ammonia, especially in its brain, but it can be concluded that, contrary to previous reports on two air-breathing catfishes (Clarias batrachus and Heteropneustes fossilis) from India, C. gariepinus does not detoxify ammonia to urea or free amino acids on land.     

Development of a bioenergetics model for fish embryos and larvae during the yolk feeding period

A mechanistic model of an energy budget in fish embryos and yolk-sac larvae was developed using data for five freshwater fish species: rainbow trout Oncorhynchus mykiss , nase Chondrostoma nasus , carp Cyprinus carpio , tench Tinca tinca and African catfish Clarias gariepinus , based on the existing models for adult and juvenile fishes. The model simulates changes in the components of the budget under various conditions. Besides the effects of body mass and temperature on consumption and metabolic rate, the dependence of ration size on amount of available yolk and initial egg size was implemented in the model. The model parameters were found through optimization. A sensitivity analysis of the model was conducted by varying its parameters and observing changes in the output. A comparative analysis showed that the values generated by the model closely approximated independent empirical observations. Simulations of energy budgets demonstrated that the overall pattern of energy partitioning was the same for different species, irrespective of egg size and temperature preferences. Most energy was allocated to body growth. Clarias gariepinus showed the fastest growth and had the highest yolk conversion efficiency.     

Helminth parasites of Clarias gariepinus (Clariidae) in Lekki Lagoon, Lagos, Nigeria

A total of 360 randomly selected specimens of Clarias gariepinus (Clariidae) recovered from Lekki Lagoon were examined for intestinal helminth parasites. Parasite prevalence and worm burden were low; 17 (4.72%) of the specimens examined were infected with gastrointestinal helminths. The helminth worms recovered include, three cestodes Polyonchobothrium clarias, Stocksia pujehuni and Wenyonia acuminata and a nematode, Paracamallanus cyathopharynx. There was no statistically significant difference in the infection of the male and female Clarias gariepinus; the infection rates in male and female samples were 5.75% and 3.76% respectively. Parasite prevalence was related to the length and weight of the specimens. The fish samples were observed to show negative allometric growth and smaller samples recorded higher helminth infection.     

Blood parasites of amphibians from Algonquin Park, Ontario

During a 5 wk period beginning May 25, 1983, 329 amphibians, which included specimens of Rana catesbeiana Shaw, Rana clamitans Latreille, Rana septentrionalis Baird, Rana sylvatica LeConte, Hyla crucifer Wied, Bufo americanus Holbrook, and Plethodon cinereus Green, from Lake Sasajewun, Algonquin Park, Ontario, Canada were examined for blood parasites. The prevalences of species of Trypanosoma, Haemogregarina, Lankesterella, Babesiasoma, and Thrombocytozoons in these amphibians were determined. Two species of microfilaria (probably Foleyella spp.) and two intraerythrocytic forms, inclusions of an icosahedral cytoplasmic DNA virus (ICDV) and groups of rickettsial organisms, were also observed. The following are new host records: Trypanosoma ranarum (Lankester, 1871) in B. americanus; Trypanosoma ranarum (Lankester, 1871) in R. sylvatica; Trypanosoma pipientis Diamond, 1950, Babesiasoma stableri Schmittner and McGhee, 1961 and Thrombocytozoons ranarum Tchacarof, 1963 in R. septentrionalis. The aquatic frogs generally showed a much higher prevalence of infection with blood parasites than the terrestrial frogs, toads and salamanders, which is suggestive of an aquatic vector. The leech Batracobdella picta Verrill, 1872, which was found on many of the aquatic frogs, is the most likely vector in the study area. Also, an increasing prevalence of parasites was noted with increasing sizes (ages) of Rana clamitans and R. catesbeiana suggesting that longer exposure to water makes these species more likely to acquire blood parasites. The presence of Trypanosoma ranarum in B. americanus appeared to coincide with their attainment of sexual maturity.     

Nutritive value of dried lactic acid fermented fish silage and soybean meal in dry diets for juvenile catfish, Clarias gariepinus (Burchell, 1822)

Dry diets containing either fish meal (C-FM) or dried fermented fish silage and soybean meal blend (1:1, ww⁻¹) (C-FS) as the sole protein source, were fed to triplicate groups of juvenile Clarias gariepinus (10.8 ± 0.3 g) at 5% body weight per day for 70 days. Catfish fed the C-FS diet showed reduced (P < 0.05) growth rate, feed conversion, protein efficiency and digestibility. Lower amounts of available amino acids in the C-FS diet resulted in inferior nutritive value for catfish growth than in the C-FM diet. Postprandial changes in plasma amino acids showed similar patterns in both diet treatments, but the maximal mean levels attained for the C-FS diet were correspondingly lower and occurred earlier than with the C-FM diet. There were no effects of feeding C-FS diet on the hepatosomatic index but carcass analysis showed that body protein deposition was lower (P < 0.05). Differences in haematocrit, haemoglobin content and liver histology were demonstrated but were not pathological. Lower digestible energy of C-FS diet also contributed to the poor performance of catfish in this treatment. Results of this study indicate that C. gariepinus cannot metabolize protein from co-dried fish silage as efficiently as fish meal protein when used as the sole dietary protein.     

Phylogenetic position of the giant anuran trypanosomes Trypanosoma chattoni,Trypanosoma fallisi,Trypanosoma mega,Trypanosoma neveulemairei,and Trypanosoma ranarum inferred from 18S rRNA gene sequences

Phylogenetic relationships within the kinetoplastid flagellates were inferred from comparisons of small-subunit ribosomal RNA gene sequences. These included 5 new gene sequences, Trypanosoma fallisi (2,239 bp), Trypanosoma chattoni (2,180 bp), Trypanosoma mega (2,211 bp), Trypanosoma neveulemairei (2,197 bp), and Trypanosoma ranarum (2,203 bp). Trees produced using maximum-parsimony and distance-matrix methods (least-squares, neighbor-joining, and maximum-likelihood), supported by strong bootstrap and quartet-puzzle analyses, indicated that the trypanosomes are a monophyletic group that divides into 2 major lineages, the salivarian trypanosomes and the nonsalivarian trypanosomes. The nonsalivarian trypanosomes further divide into 2 lineages, 1 containing trypanosomes of birds, mammals, and reptiles and the other containing trypanosomes of fish, reptiles, and anurans. Among the giant trypanosomes, T. chattoni is clearly shown to be distantly related to all the other anuran trypanosome species. Trypanosoma mega is closely associated with T. fallisi and T. ranarum, whereas T. neveulemairei and Trypanosoma rotatorium are sister taxa. The branching order of the anuran trypanosomes suggests that some toad trypanosomes may have evolved by host switching from frogs to toads.     

Stocking density affects circadian rhythms of locomotor activity in African catfish, Clarias gariepinus

The effect of stocking density on the locomotor activity of African catfish C. gariepinus under different light regimes was investigated. C. gariepinus were stocked under different densities (1, 5, or 10 fish/tank), and their locomotor activity recorded under light-dark (LD), constant light (LL), constant darkness (DD), and LD-reversed (DL) regimens. Under the LD cycle, catfish showed a crepuscular activity pattern, irrespective of stocking density, with most of the daily activity concentrated around the light-onset and light-offset times. When fish were subjected to DD, all 4 tanks with medium (5 fish) and high (10 fish) stocking densities showed circadian rhythmicity, with an average period (?) of 23.3???0.5 and 24.6???0.5?h, respectively. In contrast, only 2 low (1 fish) density tanks showed free-running rhythms. Under LL, activity levels decreased significantly in comparison with levels observed under LD and DD. Moreover, fish of 1, 2, and 3 out of the 4 tanks with low, medium, and high densities, respectively, showed free-running rhythms under these conditions. When the photocycle was reversed (DL), fish of 3, 2, and 4 out of the 4 tanks with low, medium, and high stocking densities, respectively, showed gradual resynchronization to the new phase, and transient cycles of activity were observed. These results suggest that stocking density of fish affected the display of circadian rhythmicity and the intensity of activity levels. Thus, fish kept in higher densities showed more robust rhythmicity and higher levels of daily activity, indicating that social interactions may have an influence on behavioral patterns in the African catfish.     

Sublethal effects of aquatic pollution in Lake Maryût on the African sharptooth catfish, Clarias gariepinus (Burchell, 1822)

Some aspects of the physiology and biochemistry of the African sharptooth catfish, Clarias gariepinus (Burchell, 1822), were studied along with an array of physicochemical characteristics of the water in Lake Maryût, Egypt. Data were compared to those of a reference fish hatchery. At least 11 of the conventional water pollutants (Cd, Cu, Fe, Pb, Mn, Hg, Ni, Zn, turbidity, chemical oxygen demand and ammonia nitrogen) were elevated in the most polluted main basin of the lake. In turn, serologic analysis of the indigenous catfish C. gariepinus pointed at functional impairment of the liver, heart and kidney as reflected by the elevated activities of alanine aminotransferase, aspartate aminotransferase, lactate dehydrogenase, creatine kinase, cholinesterase, glucose and creatinine. Reduced nucleic acid measurements [the ratio RNA/DNA and the relative RNA content (r)] indicated diminished protein synthesis and impaired growth in polluted fish. In some instances, glucose and nucleic acid measures were elevated in favour of fish from moderately polluted basins of the lake rather than in reference fish. Fish seemed to profit from the typical geographical habitat in the lake, regardless of the virtual contamination there, versus reference fish that seemed to suffer congestion stress and food competition in the confined and overcrowded commercial pond.     

Observations on agonistic behaviour of Clarias gariepinus larvae and juveniles under different densities and feeding frequencies in a controlled environment

Ten-day-old African catfish larvae, Clarias gariepinus , were stocked in aquaria at 5, 13, 22, and 30 larvae per liter with fish at each density being fed three and six times per day over 35 days. Fish were fed with an artificial diet in excess of their satiation requirements at each feeding. Every week total length was determined for samples of 25 fish per tank and all fish were counted at weekly intervals. Behaviour patterns were categorized into timed behaviour (i.e. resting, swimming and browsing), and frequency events e.g. number of contacts, aggressive contacts and number of head or body attacks. Fish at the lowest density grew faster than fish at the other densities. Feeding frequency had no effect on growth. With increasing densities fish less frequently changed timed behaviour patterns while spending a greater percentage of the time swimming. Aggressive behaviour was highest at the lowest density but remained uninfluenced at densities greater than five fish per litre. The high feeding frequency provoked a higher rate of aggressive contacts than the low feeding frequency. A suggested explanation was that these fish were more often in anticipation of food and consequently more active between feedings. In summary, it was shown that density had an effect on duration behaviour patterns such as resting and swimming, while feeding frequency significantly influenced frequency events, in particular the rate of aggressive behaviour. The study contributes to an understanding of factors influencing C. gariepinus juvenile behaviour and suggestions for follow-up experiments are discussed.     

Abstracts

Lake Agmon was created in the Hula Valley in Israel, in the northern part of the dried-up Hula Lake site, in summer, 1994. Samples of fish at ten stations were taken by electroshocker once a month, from January to December, 1996. The fish species whose food composition in the gut was examined in this study were: Tilapia zillii, Gambusia affinis, Clarias gariepinus, Cyprinus carpio, Pseudophoxinus kervillei, Acanthobrama lissneri, Hemigrammocapoeta nana and Oreochromis aureus. Food components were determined qualitatively and quantitatively. Assessment of the organism biomass in the gut contents was based on available data of phytoplankton and zooplankton. The food of G. affinis changed during the year, consisting high level of algae in winter and spring, and insects and crustaceans in summer. In T. zillii, a high percentage of algae were found in winter, and a high percentage of plants in summer. The food of H. nana consisted mainly of phytoplankton, but included high plants during most months; P. kervillei ingested mainly insects and crustaceans, with a high percentage of Daphnia spp.; and the diet of C. gariepinus comprised fish and invertebrates species, which varied with the seasons. C. carpio ate mainly invertebrates; O. aureus are vegetarian, and A. lissneri fed on both animals and plants. This revised version was published online in July 2006 with corrections to the Cover Date.     

Immunological study of muscle parvalbumin isotypes in three African catfish during development

Eleven parvalbumin isotypes expressed during the development of clariids Heterobranchus longifilis and Clarias gariepinus and claroteid Chrysichthys auratus were purified and electrophoresed on sodium-dodecyl-sulfate polyacrylamide gels. Immunochemical cross-reactions among these proteins were investigated by immunoblotting, using purified antibodies raised against three isotypes chosen at different stages of fish development. Antibodies raised against H. longifilis PA I (larval-juvenile isotype) and against C. gariepinus PA IIIa (juvenile-adult isotype) cross-reacted to a rather similar extent despite a weaker cross-reaction of anti-PA IIIa with larval-juvenile isotypes. On the other hand, antibodies raised against H. longifilis PA IV (an exclusively adult isotype) recognized markedly only H. longifilis PA IV and C. gariepinus PA IIIb. These two adult isotypes most likely belong to the alpha lineage, and all the others to the beta lineage. These results show that parvalbumin isotypes synthesized at different stages of fish growth differ structurally, and that the most marked difference is between larval-juvenile and adult clariid isotypes.     

Temperature-induced changes of early development and yolk utilization in the African catfish Clarias gariepinus

Artificially fertilized eggs and yolk-sac larvae of a freshwater tropical/subtropical fish Clarias gariepinus receiving no external food were incubated at 22, 25 and 28° C until full yolk resorption. Developmental time, size and matter composition (CHNS-O Analyzer and ashing) were assessed at egg fertilization, hatching and yolk resorption; respiration was measured every 4–5 h. The course of acceleration of C. gariepinus embryonic developmental rate with temperature ( Q_{10 dev}) was compared over the temperature range to those of Cyprinus carpio and Oncorhynchus mykiss ; they differed greatly, but were similar when compared on the basis of effective temperatures specific to each fish. Specific growth rates for energy (88, 150 and 183% per day at 22,25 and 28° C, respectively) as well as the conversion efficiencies of egg energy (64, 71 and 68%, respectively) and protein (71, 78 and 76%, respectively) in C. gariepinus larval tissues were higher than those known for the endogenous feeding period of coldwater and temperate fish species. In C. gariepinus at the end of yolk resorption, the carbon percentage and caloric values of dry weight, size (in terms of dry matter, minerals, protein and energy per larva) and transformation efficiencies were lowest at 22° C, highest at 25° C and had slightly decreased at 28° C. A tentative mechanism which leads to the positive or negative response of body size to temperature over the viable temperature range is defined.     

Increased production of docosahexaenoic acid (22: 6 n-3, DHA) in catfish nutritionally stressed by the feeding of oxidized oils and the modulatory effect of dietary α-tocopheryl acetate

Production of hepatic docosahexaenoic acid in juvenile Clarias gariepinus was significantly increased ( P <0.05) by ingestion of rancid diets and this effect was modulated by dietary vitamin E. This has not been described previously in fish. Causal mechanisms are postulated.     

Effects of in vivo crude human chorionic gonadotropin on ovulation and spawning of the African catfish, Clarias gariepinus Burchell–1822

The effects of increasing dosages of crude human chorionic gonadotropin (cHCG) on ovulation and spawning of Clarias gariepinus Burchell were examined. Four and 5 mg cHCG/100g body weight of fish gave the best response. The activation of the interrenals and stimulation of the ovary are discussed as a possible route of in vivo human chorionic gonadotropin administration on ovulation and spawning in catfish.     

Novel function of recombinant pituitary adenylate cyclase-activating polypeptide as stimulator of innate immunity in African catfish (Clarias gariepinus) fry

There are several studies that clearly indicate a close bidirectional communication between the neuroendocrine and immune systems. In this sense, hypothalamic releasing hormones, besides their neuroendocrine role, have been shown to influence immune functions. Despite studies developed in mammals, there is, as yet, no information available about the role of the pituitary adenylate cyclase-activating polypeptide (PACAP) and PACAP-related peptide (PRP) in the fish innate immune system. The present study has evaluated the effect of PACAP and PRP administered by bath immersion, on important parameters of innate immunity and antioxidant defenses in African catfish (Clarias gariepinus) fry. We have shown, for the first time, that administration of recombinant C. gariepinus PACAP not only promotes growth but also increases lysozyme, nitric oxide synthase-derived metabolites and antioxidant defenses in treated fry. From our results, PACAP appears to act as a regulator of the teleostean immune system, in addition to its physiological role in controlling growth of fish.     

Assessment of heavy-metal profile of the New Calabar River and its impact on juvenile Clarias gariepinus

We have determined the heavy-metal status of the lower reaches of the New Calabar River in the Niger Delta region over a 40-km-long distance, and its impact on the development of catfish (juvenile Clarias gariepinus). The total mean concentrations of dissolved trace metals in the river were 0.01, 0.85, 0.56, 2.08, 0.05, 12.0, and 6.59 mg/l for Hg, Pb, Cd, Cu, Cr, Fe, and Zn, respectively. The accumulated concentration of trace metals in the muscles of different mature fish caught from the river were examined, and the results fell within the action levels adopted in most countries. To evaluate the contributions of trace metals to fisheries depletion, eggs of C. gariepinus were hatched in dilution water spiked with the total mean metal levels determined in the river water. Our results indicate substantive inhibition of egg hatch even at very low concentrations of the majority of the trace metals studied, with mortality rates well above 50% after 216 h of exposure (Table 5). These findings suggest that trace metals (except for Zn), even at very low concentrations, negatively affect fish hatch and fry rearing, implying that aquatic milieus contaminated by trace metals are not suitable as nursery grounds for fish cultures.