The biomass and yield of the dominant fish species in Hartbeespoort Dam,South Africa

The standing stocks of the three dominant fish species in Hartbeespoort Dam, O. mossambicus, C. gariepinus and C. carpio, were determined by mark and recapture experiments and Leslie's method of fishing success. The biomass of O. mossambicus increased from 279 t in 1982 to 521 t in 1983, following good recruitment to the population after a year's mild winter mortality. Only one reliable estimate of each of the other two species could be made, C. gariepinus (293 t) and C. carpio (581 t). The fish community was heavily utilised by recreational anglers and the estimated mean annual yields were O. mossambicus (144 t), C. gariepinus (102 t) and C. carpio (449 t). These yields are probably higher than the longer term mean harvest as a result of low water levels during the study period, which increased catchability. The high standing stocks and yields are ascribed to high nutrient concentrations and primary production.     

Health assessment of freshwater fish species from Albasini Dam,outside a DDT-sprayed area in Limpopo province,South Africa: a preliminary study

During 2006 to 2008, the water, sediment and fish in Albasini Dam, used as a reference site outside a DDT-sprayed area, had been found to be as affected as those in the nearby DDT-sprayed area were. Accordingly, the aim of the current study, conducted in 2014, was to determine the health status of fish from Albasini Dam by means of a histology-based fish health assessment protocol. High levels of nitrates, as well as the organochlorine pesticides aldrin, dieldrin, chlordane and methoxychlor, were found in the water. Fish muscle tissue contained pesticides, including methoxychlor. A semi-quantitative histological assessment on Clarias gariepinus, Coptodon rendalli and Oreochromis mossambicus showed diverse histopathology in selected target organs, with the gills being most affected. Notably, the testis tissue of one C. rendalli was filled with eosinophilic liquid, characteristic of necrosis. Microscopic intersex was found in two of the nine O. mossambicus sampled. This is the second time that intersex as microscopic testicular oocytes has been reported in O. mossambicus in South Africa. This finding perhaps indicates that reproduction may be compromised and this will be investigated further. The presence of intersex and other histopathology in organs could be early warning signs of the declining water quality in this dam.     

Age,growth and reproduction of Marcusenius pongolensis,Oreochromis mossambicus and Schilbe intermedius in an oligotrophic impoundment in Swaziland

The age, growth and reproductive biology of Marcusenius pongolensis, Oreochromis mossambicus and Schilbe intermedius were investigated in the Mnjoli Dam, Swaziland. Otolith annulus formation occurred in winter for M. pongolensis, and in spring/summer for O. mossambicus and S. intermedius. Maximum ages of 8, 6 and 8 years were recorded for M. pongolensis, O. mossambicus and S. intermedius, respectively. Growth was described by the von Bertalanffy growth model as L_t = 238.73(1 − exp^{−0.27(t+2.27}) mm fork length (FL) for M. pongolensis, L_t = 226.83(1 − exp^{−0.45(t+2.02)}) mm total length (TL) for O. mossambicus, and L_t = 214.59(1 − exp^{−0.60(t+1.20)}) mm FL for S. intermedius. Sexual maturity was estimated for male and female M. pongolensis at 134 mm FL and 119 mm FL, respectively. Marcusenius pongolensis matured within their first year. Female O. mossambicus and S. intermedius matured at 239 mm TL and 205 mm FL, corresponding to 2 and 4 years of age, respectively. Extended spawning periods, with two spawning peaks was observed for M. pongolensis, one in spring (September) and the second in autumn (March) and one peak over late‐summer for S. intermedius.     

Postprandial changes in pH and enzyme activity from the stomach and intestines of Tilapia rendalli (Boulenger, 1897), Oreochromis mossambicus (Peters, 1852) and Clarias gariepinus (Burchell, 1822)

The ability to utilise dietary components differs among fish species. Digestive enzymes may be used to determine the efficiency of the digestive process. In this study, the activities of the digestive enzymes in Tilapia rendalli, Oreochromis mossambicus and Clarias gariepinus were explored. Protease, amylase, lipase and cellulase activities were measured in different parts of the digestive tract of the three fish species. The pH dynamics along the digestive tract were monitored. In all fish species, the presence of food led to a reduction in stomach pH, whereby pH values of 1.54, 1.58 and 2.01 were recorded 12 h after feeding in O. mossambicus, T. rendalli and C. gariepinus, respectively. Protease and amylase activities were significantly higher (P < 0.05, anova ) in the tilapias than in C. gariepinus. The tilapias may be pre‐adapted to produce more protease and amylase to digest plant material, which is more difficult to digest than animal matter. In all species amylase activity was significantly higher in the proximal intestine than in the other parts of the digestive tract (P < 0.05, anova ). The highest protease activity was recorded in the distal intestines. This is because of the alkaline pH recorded in the proximal and distal intestines, which favours amylase and protease activity, respectively. Lipase activities were significantly higher (P > 0.05) in C. gariepinus than in both tilapias. Marginal cellulase activities were recorded in all species. It is inferred here that phylogeny and not diet may be the main factor influencing enzyme activities, as all fish were fed a similar diet.     

Food and feeding habits of Clarias mossambicus from four areas in the Lake Victoria basin,East Africa

Synopsis The food and feeding habits of Clarias mossambicus in four habitat types in the northern Lake Victoria basin were studied. The importance of certain food types to this species varies from area to area. In the lake, rivers and swamps, C. mossambicus fed mainly on fish, particularly Haplochromis species. In the sewage ponds, Crustacea and insects were the main food items. The extent of ingestion by C. mossambicus of a given food type presumably reflects the availability and abundance of the food in the habitat. This constitutes a shift in the food habits which is of vital importance in this migratory fish. By employing several feeding methods, i.e. hunting, bottom feeding, surface feeding and filter feeding, C. mossambicus exploits a broad spectrum of food resources in the various habitats.Many modern workers consider Clarias mossambicus conspecific with C. gariepinus and a junior synonym of the latter (Editor)     

Health and chemical burdens of fish species from polluted and hyper-eutrophic freshwater ecosystems in South Africa

Three aquatic ecosystems in South Africa, the Hartbeespoort, Klipvoor and Bospoort Dams, are classified as hyper-eutrophic, because of high nutrient loads and chemical pollution. Water and two fish species, Clarias gariepinus and Cyprinus carpio, were collected from these dams to assess the impact of eutrophication and chemical pollutants on their health status. Water and muscle samples were analysed for organic and inorganic chemicals. Condition factor was determined and a necropsy performed to note any macroscopic abnormalities. A histology-based fish health assessment was done on the liver, kidney, gills and gonads. A number of fish from the three dams exhibited livers with fatty change and focal discoloration, skin lesions and parasites within the visceral cavity. The prevalence and severity of histopathology in the liver resulted in higher liver index values than the index values for kidneys and gills. Aluminium, silicon and chromium were detected in the water and muscle tissue. The DDT metabolite p,p’-DDE was present in both species, as well as in fish from the reference site, Marico-Bosveld Dam. Only C. gariepinus from Hartbeespoort Dam had p,p’-DDD levels higher than 5 µg g^?1 per edible portion. Water from hyper-eutrophic dams adversely affects the health of freshwater fish.     

The geographic variation and potential risk of DDT in the blood of Pied Kingfishers from northern KwaZulu-Natal,South Africa

Evans, S.W. & Bouwman, H. 2000. The geographic variation and potential risk of DDT in the blood of Pied Kingfishers from northern KwaZulu-Natal, South Africa. Ostrich 71 (1 & 2): 351–354.

DDT has, since 1946 been used in the intradomicilliary control of malaria in northern KwaZulu-Natal. The Pied Kingfisher was selected as representative for organisms in relatively high trophic levels. Blood was obtained from Pied Kingfishers at Kosi Bay (n = 5), Pongolo Floodplain (n = 13), Mkuzi Nature Reserve (n = 4), Ndumu Nature Reserve (n = 4) and St Lucia (n = 3), extracted and analysed [SWEl] via gas chromatography. The highest blood DDE and σDDT concentrations were obtained for the birds from the Pongolo Floodplain (means of 95.92 μg 1^?1/107.01 μg μg 1^?1) and Kosi Bay Nature Reserve (means of 189.09 μg 1^?l/241.8 μg 1^?1). DDT was detected in the blood of Pied Kingfishers from Kosi Bay (mean 47.14 μg 1^?1) and Pongolo Floodplain (mean 44.34 pg 1^?1) only. This indicated their proximity to DDT application and the greater influx of DDT and its metabolites into the water component of these systems. The EDDT plasma concentrations in the Pied Kingfisher blood were calculated by multiplying the blood values of σDDT by 1.8. Using the regression, log₁₀Y = 0.7785 + 0.8593 (log₁₀X), relating the σDDT in eggs to σDDT in plasma of American Kestrel Falco sparverius it was possible to calculate the mean Pied Kingfisher egg σDDT concentration. The approximate mean Pied Kingfisher egg concentration of σDDT was calculated at 2.26 mg kg^?1 for Kosi Bay and 1.24 mg kg^?1 for the Pongolo Floodplain. Using the highest calculated plasma value of σDDT for Kosi Bay and the Pongolo Floodplain indicated that egg σDDT concentrations could be as high as 4.01 mg kg^?1 and 4.17 mg kg^?1 respectively. These calculated levels may be significant when compared to levels of DDE, known to have a detrimental effect, in the eggs of the Brown Pelican Pelecanus occidentalis, where a concentration of 2.5 to 3 mg kg^?1 was associated with substantially impaired reproductive success. The highest calculated egg concentration was nearing this level and it is therefore possible that the Pied Kingfisher population may be at risk.     

Trophic interrelationships between the exotic Nile tilapia, <Emphasis Type="Italic">Oreochromis niloticus</Emphasis> and indigenous tilapiine cichlids in a subtropical African river system (Limpopo River,South Africa)

The stable isotope ratio and seasonal changes in diet of two indigenous (Oreochromis mossambicus, Tilapia rendalli) and one exotic (Oreochromis niloticus) tilapiine cichlids in the subtropical Limpopo River, South Africa were investigated to determine patterns of resource partitioning. Stomach contents of O. niloticus and O. mossambicus indicated high dietary overlap across size class, habitat and season, with both species primarily feeding on vegetative detritus. However, stable isotope analysis revealed that the two Oreochromis species had different stable isotope ratios derived from different food sources. The relatively δ¹³C-depleted O. niloticus indicates a phytoplankton-based diet, while the δ¹³C-enriched O. mossambicus indicates a macrophagous diet dominated by vegetative detritus and periphyton. The high similarity in stomach contents and the interspecific differences in isotopic composition reveal fine-scale patterns of food resource partitioning that could be achieved through selective feeding. Tilapia rendalli was largely macrophagous and fed mainly on aquatic macrophytes and had a low dietary overlap with both O. niloticus and O. mossambicus. In the Limpopo River, detritus and algae are probably the most abundant food resources and the causal factors responsible for the observed patterns of resource partitioning among the tilapiines are usually difficult to ascertain. Fish may be able to perceive food resources in terms of the dynamics that determine their availability. Detailed studies of variation in food resource availability and fish habitat use within the system are needed to evaluate this hypothesis.     

The properties of tilapia sperm and its cryopreservation*

The specific differences between the testis, milt and sperm of six species of tilapia including Oreochromis aureus, O. mossambicus, O. niloticus, Tilapia zillii, O. nilolicus×O. aureus hybrid and red tilapia, Oreochromis sp., were studied. The shape of testis is tubular; the gonadosomatic index varied from 0.07 to 2.71. The pH values of individual milts ranged from 6.2 to 8.2 and the osmolarity from 240 to 380 mOsmol kg^?1. The quantity of milt obtained by stripping averaged only about 0.3 ml, and only in the O. niloticus×O. aureus hybrid did it exceed 3 ml. Sperm motility graded from weak to moderate was determined for the stripped tilapia milt. Sperm concentrations ranged from 7.70 × 10⁸ sperms ml^?1 in T. zillii to 2.74 × 10¹⁰ sperms ml^?1 in O. mossambicus. Tilapia sperm was active in various salinity ranges such as 0–5‰ for O. niloticus, and 0–15‰ for O. mossambicus and T. zillii. Extender containing 15% milk and 5% methanol was used to prepare milt mixture before cooling rapidly to ?35° C and then at 5° C min^?1 to ?75° C for storage in liquid nitrogen (– 196° C). Fertility tests on frozen tilapia milt resulted in a fertilization rate of 72.7% (v. control 85.7%) for the 22-day frozen milt of the O. nilolicus×O. aureus hybrid used to fertilize the eggs of O. honorum, and 93.4% (v. control 90%) for the 304-day frozen sperm of red tilapia used to fertilize eggs of red tilapia.     

The sublethal effects of zinc at different water temperatures on selected haematological variables in Oreochromis mossambicus

Trace metals such as zinc play an important role in the normal metabolic functioning of all organisms. However, metals can become toxic if background concentrations are exceeded in the environment. This study investigated the sublethal effects of zinc on the haematology of Oreochromis mossambicus at different water temperatures. Fish were exposed to sublethal zinc (Zn) concentrations of 40μg/l (mean Zn concentration measured from the Mhlathuze River) for a period of 96h at different water temperatures representing the seasonal temperatures in the Mhlathuze River (18°C, 24°C, 28°C and 32°C). Exposure to zinc at 28°C and 32°C resulted in the most pronounced haematological changes in O. mossambicus. The erythrocytotic conditions found following exposure to Zn could be attributed to damage to the gill surface. The ensuing hypoxic conditions are alleviated through the release of large amounts of immature RBC into the circulatory system. The leucocytotic conditions support the findings of damage to the gill surface. The increased glucose concentrations were attributed to a general adaptation response whereby metabolites are mobilised to meet increased energy demands during periods of stress. The changes in Na⁺ and K⁺ levels in the plasma of O. mossambicus can be attributed to a combination of stimulation of Na-K ATPase activity, reduced membrane permeability in the gill tissue and leakage from cells into the blood, respectively.     

Sperm motility parameters for Steindachneridion parahybae based on open‐source software

The objective of this work was to evaluate the sperm motility of 13 Steindachneridion parahybae males using open‐source software (ImageJ/CASA plugin). The sperm activation procedure and image capture were initiated after semen collection. Four experimental phases were defined from the videos captured of each male as follows: (i) standardization of a dialogue box generated by the CASA plugin within ImageJ; (ii) frame numbers used to perform the analysis; (iii) post‐activation motility between 10 and 20 s with analysis at each 1 s; and (iv) post‐activation motility between 10 and 50 s with analysis at each 10 s. The settings used in the CASA dialogue box were satisfactory, and the results were consistent. These analyses should be performed using 50 frames immediately after sperm activation because spermatozoa quickly lose their vigor. At 10 s post‐activation, 89.1% motile sperm was observed with 107.2 μm s^?1 curvilinear velocity, 83.6 μm s^?1 average path velocity, 77.1 μm s^?1 straight line velocity; 91.6% were of straightness and 77.1% of wobble. The CASA plugin within ImageJ can be applied in sperm analysis of the study species by using the established settings.     

A note on copper bioaccumulation in Mozambique tilapia,Oreochromis mossambicus (Osteichthyes: Cichlidae)

Copper (Cu) is one of the most commonly reported metal pollutants in African water bodies, but there are few studies on African freshwater fish species of copper accumulation and copper toxicity. Adult O. mossambicus were exposed to 0mg l^?1 (control) and 0.75mg l^?1 Cu for 96h and 0 (control), 0.11, 0.29 and 0.47mg l^?1 copper for 64 days. Samples of liver and gills were collected after 96h, and after 1, 32 and 64 days, respectively. There were significant differences in the mean Cu accumulation values in the liver and gills between the control and the Cu-exposed fish after the 96-h exposure. In fish exposed to 0.11 and 0.29mg l^?1 Cu for 64 days there was an increase in copper level in the tissues. In fish exposed to 0.47mg l^?1 Cu the concentration in the gill and liver tissue did not increase between Day 1 and Day 32. At this time, Cu accumulation in the liver was higher than for fish exposed to 0.11 and 0.29mg l^?1 Cu for 64 days. Exposure to approximately 0.47mg l^?1 Cu for more than 32 days induced mortality.     

Hybridization and phylogeography of the Mozambique tilapia <Emphasis Type="Italic">Oreochromis mossambicus</Emphasis> in southern Africa evidenced by mitochondrial and microsatellite DNA genotyping

Many Oreochromis species utilized in aquaculture were extensively introduced outside their native range in Africa. Given their recent evolutionary radiation, these species hybridize easily, posing a threat to the integrity of local adaptation. The objective of this work was to study the genetic diversity of the Mozambique tilapia (Oreochromis mossambicus) in its native range, southern Africa, and provide a method for identifying hybrids with genetic markers. We genotyped the mitochondrial DNA (mtDNA) control region (385 bp) of wild and farmed O. mossambicus, wild and farmed O. niloticus and morphologic wild hybrids. These data were complemented with published sequences of parapatric and sympatric Oreochromis taxa. Phylogeographic analysis showed the presence of two O. mossambicus lineages, the southernmost representing a recent Holocene radiation. Hybridization of O. mossambicus was indicated by the presence of O. niloticus and O. mortimeri–andersonii mtDNA specimens in the Limpopo basin and of O. karongae mtDNA in specimens from Malawi. We also genotyped seven suspected hybrid individuals from the Limpopo River, and 137 wild and farmed Mozambique and Nile tilapia samples with five microsatellite markers. Factorial Component Analysis, Bayesian clustering and assignment analyses consistently delineated an O. mossambicus and an O. niloticus group, with the putative hybrids positioned in between. Different levels of hybridization were detected by the Bayesian assignment. The complex nature of hybridization and introgression between cichlid species raises major concerns for the long-term integrity of Mozambique tilapia.     

Synergistic inhibition of metabolic cooperation by oleic acid or 12-0-tetradecanoylphorbol-13-acetate and dichlorodiphenyltrichlorethane (DDT) in Chinese hamster V79 cells: Implication of a role for protein kinase C in the regulation of gap junctional intercellular communication

The effects of TPA and/or DDT and oleic acid and/or DDT on gap junction-mediated intercellular communication (i.e. metabolic cooperation) between Chinese hamster V79 cells was examined. Addition of TPA, DDT or oleic acid alone to cocultures of 6t-hioguanine-resistant (6-TG ^R ) and 6-thioguanine-sensitive (6-TG ^S ) V79 cells significantly increased the recovery of 6-TG ^R cells indicating inhibition of metabolic cooperation. In the presence of TPA and DDT or oleic acid and DDT the observed recovery of 6-TG ^R cells was significantly greater than the expected (calculated) additive 6-TG ^R cell recovery. No synergistic increases in 6-TG ^R cell recovery were observed when co-cultures of V79 cells were exposed to dieldrin and DDT. These results indicate that TPA and DDT or oleic acid and DDT can act synergistically to inhibit metabolic cooperation. These data suggest a role for protein kinase C in the regulation of gap junction-mediated intercellular communication.Abbreviations DDT dichlorodiphenyltrichlorethane - MC metabolic cooperation defective - 6-TG 6thioguanine - TPA 12-0-tetradecanoylphorbol-13-acetate     

Chromosomal localization of rDNA genes and genomic organization of 5S rDNA in <Emphasis Type="Italic">Oreochromis mossambicus,O. urolepis hornorum</Emphasis> and their hybrid

In this study, classical and molecular cytogenetic analyses were performed in tilapia fishes, Oreochromis mossambicus (XX/XY sex determination system), O. urolepis hornorum (WZ/ZZ sex determination system) and their hybrid by crossing O. mossambicus female × O. u. hornorum male. An identical karyotype ((2n = 44, NF (total number of chromosomal arms) = 50) was obtained from three examined tilapia samples. Genomic organization analysis of 5S rDNA revealed two different types of 5S rDNA sequences, 5S type I and 5S type II. Moreover, fluorescence in situ hybridization (FISH) with 5S rDNA probes showed six positive fluorescence signals on six chromosomes of all the analysed metaphases from the three tilapia samples. Subsequently, 45S rDNA probes were also prepared, and six positive fluorescence signals were observed on three chromosome pairs in all analysed metaphases of the three tilapia samples. The correlation between 45 rDNA localization and nucleolar organizer regions (NORs) was confirmed by silver nitrate staining in tilapia fishes. Further, different chromosomal localizations of 5S rDNA and 45S rDNA were verified by two different colour FISH probes. Briefly, the current data provide an insights for hybridization projects and breeding improvement of tilapias.     

Computer-assisted sperm analysis of fresh epididymal cat spermatozoa and the impact of cool storage (4 degrees C) on sperm quality

Epididymal cat sperm is commonly used for in vitro fertilization. Because of the high variability in preparation protocols and methods of evaluation, sperm quality may vary considerably between experiments and laboratories. The aims of the present study were (1) to describe an epididymal sperm preparation protocol to produce clean, highly motile samples using density gradient centrifugation, (2) to provide reference values of computer-assisted semen analysis (CASA) parameters of fresh epididymal cat sperm after density gradient centrifugation and (3) to investigate the effect of cool storage on various spermatozoa characteristics. After slicing the epididymides, viable and motile sperm cells were isolated using Percoll^® centrifugation. Sperm motility parameters were subsequently assessed using CASA in experiment 1. In experiment 2, fresh (day 0) sperm samples were evaluated for motility parameters (HTR) and stained for assessment of acrosomal status (FITC-PSA), morphology (eosin/nigrosin (E/N)), membrane integrity (E/N and SYBR^®14-PI) and DNA fragmentation (TUNEL). After addition of a Tris–glucose-citrate diluent containing 20% egg yolk, samples were cooled to 4 °C and reassessed on d1, d3, d5, d7 and d10. Cool storage impaired most motility and velocity parameters: MOT, PMOT, VAP, VSL, VCL, BCF, RAPID and the percentage of normal spermatozoa showed a decrease over time (P < 0.05) as compared to fresh samples. In contrast, STR, ALH, membrane integrity, DNA fragmentation and the percentage of acrosome intact spermatozoa were not affected by cool storage. However, the influence of cool storage of cat spermatozoa on subsequent in vitro embryo development and quality after IVF requires further investigation.     

Stunting in Oreochromis mossambicus (Peters) (Pisces, Cichlidae): An evaluation of past and recent data from Sri Lankan reservoir populations

Tilapiine fish are known to become stunted under different environmental conditions. Of the tilapia, Oreochromis mossambicus (Peters), once considered to be the aquatic chicken, is now treated as a nuisance species in some countries because of its tendency to stunt easily. O. mossambicus is the mainstay of the commercial gillnet fishery in existence in the multitude of reservoirs in Sri Lanka for over 35 years. Published and new evidence on O. mossambicus population traits are presented with a view to evaluating whether the populations in Sri Lankan reservoirs are stunted or not. The main lines of evidence considered are the mean size at maturity (Lm), the proportion of individuals below 20 cm total length in the commercial landings, and growth performance of the individual reservoir populations. Statistically valid inter-relationships exist between the mean length at maturity and the proportion of undersized individuals (below 20 cm) in the landings, and the ratio of the reservoir catchment or watershed area to surface area. Evidence on Lm indicate that there is a tendency for O. mossambicus populations to stunt, however, evidence on growth and mean landing size do not indicate stunting.     

Piscivory does not cause pansteatitis (yellow fat disease) in Oreochromis mossambicus from an African subtropical reservoir

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Acute toxicity and adverse effects of aqueous and ethanol extracts of Parkia biglobosa pods on biochemical parameters of Clarias gariepinus

The acute toxicity of the aqueous and ethanol extracts of Parkia biglobosa pods against Clarias gariepinus was investigated under laboratory conditions. Agitated behaviours and respiratory distress were also observed during the exposure period. The adverse effects on biochemical parameters were assessed using semi-static bioassays for 28 days. The ethanol extract of P. biglobosa pods was found to be more acutely toxic with a 96 h LC₅₀ value of 13.96 mg l^?1 than the aqueous extracts, with a 96 h LC₅₀ value of 19.95 mg l^?1 against C. gariepinus. Both extracts induced agitated behaviours and respiratory distress in exposed organisms. The activities of superoxide dismutase (SOD), catalase (CAT) and the concentration of malondialdehyde (MDA) were significantly lower (p < 0.05) in groups of organisms exposed to extracts of P. biglobosa when compared with the control group after 14 days. The activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (ALP) were also significantly (p < 0.05) lower compared with activities of the enzymes in the control group after 28 days. The current study has shown that the introduction of P. biglobosa pods into aquatic ecosystems is acutely toxic to fish and would possibly be to other non-target aquatic organisms especially invertebrates.     

Cloning of a neoteleost (Oreochromis mossambicus) pro-opiomelanocortin (POMC) cDNA reveals a deletion of the γ-melanotropin region and most of the joining peptide region: implications for POMC processing

A signature feature of tetrapod pro-opiomelanocortin (POMC) is the presence of three melantropin (MSH) coding regions (α-MSH, β-MSH, γ-MSH). The MSH duplication events occurred early during the radiation of the jawed vertebrates well over 400 million years ago. However, in at least one order of modern bony fish (subdivision Teleostei; order Salmoniformes; i.e. salmon and trout) the γ-MSH sequence has been deleted from POMC. To determine whether the γ-MSH deletion has occurred in other teleost orders, a POMC cDNA was cloned from the pituitary of the neoteleost Oreochromis mossambicus (order Perciformes). In O. mossambicus POMC, the deletion is more extensive and includes the γ-MSH sequence and most of the joining peptide region. Because the salmoniform and perciform teleosts do not share a direct common ancestor, the γ-MSH deletion event must have occurred early in the evolution of the neoteleost fishes. The post-translational processing of O. mossambicus POMC occurs despite the fact that the proteolytic recognition sequence, (R/K)-X_n-(R/K) where n can be 0, 2, 4, or 6, a common feature in mammalian neuropeptide and polypeptide hormone precursors, is not present at several cleavage sites in O. mossambicus POMC. These observations would indicate that either the prohormone convertases in teleost fish use distinct recognition sequences or vertebrate prohormone convertases are capable of recognizing a greater number of primary sequence motifs around proteolytic cleavage sites.