Showing papers in "Aquaculture Research in 1991"
TL;DR: The mean increase in African catfish weight with time over the entire larval period can be approximated by a cubic or exponential growth model, but the growth rate indices specific growth rate (k) and the regression coefficient of a cube root transformation of the weight data (b), both vary significantly when measured over successive short intervals from first feeding.
Abstract: . The mean increase in African catfish, Clarias gariepinus (Burchell), weight with time over the entire larval period can be approximated by a cubic or exponential growth model. However, the growth rate indices specific growth rate (k) and the regression coefficient of a cube root transformation of the weight data (b), both vary significantly when measured over successive short intervals from first feeding. In particular, the onset of air breathing is associated with a significant depression in growth rate. The variation in specific growth rate (k) with larval age closely approximates the relationship between mean % increase in body weight per day and larval age; however, the cube root regression coefficient does not share this property. In addition to the effect of larval age the growth rate of African catfish larvae is significantly affected by the initial density at which they are stocked (between 25 and 250 larvae/1) and interactions between age and stocking density. Survival over the larval period, of 80% or more, is apparently unaffected by initial stocking density (between 50 and 250larvae/I); however, the onset of air breathing in particular is associated with an increase in fish deaths.
119 citations
TL;DR: A strong and significant positive correlation was observed between condition factor and total lipid content in immature Atlantic salmon sampled at the same time and can be used as a convenient non-lethal indicator of energy reserve status among immature salmonids.
Abstract: . A strong and significant positive correlation was observed between condition factor and total lipid content in immature Atlantic salmon, Salmo salar L., parr (0+) sampled at the same time. Condition factor can thus be used as a convenient non-lethal indicator of energy reserve status among immature salmonids.
116 citations
TL;DR: Electivity was found to be low in most instances, although the low productivity of the ponds may have had some influence, and dietary overlap was greatest between catla and silver carp.
Abstract: . The fry of four species of planktivorous carp, silver carp, Hypophthalmichthys molitrix (Valenciennes), bighead carp, Aristichthys nobilis (Richardson), rohu, Labeo rohita (Hamilton), and catla, Catla catla (Hamilton), were grown in monoculture in ponds in Mymensingh, Bangladesh in order to determine electivity and the extent of dietary overlap. Other than an avoidance for Cyanobacteria, electivity was found to be low in most instances, although the low productivity of the ponds may have had some influence. Dietary overlap was greatest between catla and silver carp (0–52) and between catla and bighead carp (0–48).
112 citations
TL;DR: Differences in scale characters between fanned, ranched and wild Atlantic salmon, Salmo salar h.
Abstract: . This study describes differences in scale characters between fanned, ranched and wild Atlantic salmon, Salmo salar h., and proposes a method to distinguish between the different groups. Six characters were found to differ: (1) smolt size; (2) smolt age; (3) transition from fresh water to salt water; (4) sea winter bands; (5) summer checks; (6) replacement scales. The combined use of these characters in a score system gave good separation between fanned and wild salmon, but not for ranched salmon.
98 citations
TL;DR: The pre-acidification level of Atlantic salmon, Salmo salar L., production in Norway was estimated from accessible rearing habitat, potential smolt production, smolt to adult survival, and mean adult weight.
Abstract: . The pre-acidification level of Atlantic salmon, Salmo salar L., production in Norway was estimated from accessible rearing habitat, potential smolt production, smolt to adult survival, and mean adult weight. Atlantic salmon have been virtually lost in 25 rivers due to acidification. In total, 340.6km of river is affected, and this corresponds to a rearing area of 2044.8 ha. The total annual number of adult salmon lost was estimated to be between 92016 and 306720 individuals, weighing some 345-1150 tonnes.
62 citations
TL;DR: Protein from poultry sources was digested better by tilapia than by carp or catfish, but no significant difference was found in the case of protein mainly from fish meal, and the same pattern applies to the digestibility of energy.
Abstract: . This paper examines the digestibility of different feed mixtures by three species of fish: carp, Cyprinus carpio L., tilapia, Oreochromis aureus×O. niloticus, and African catfish, Clarias gariepinus (Burchell 1822). Protein from poultry sources was digested better by tilapia than by carp or catfish, but no significant difference was found in the case of protein mainly from fish meal. Carp showed the best ability to digest fats, followed by catfish, with tilapia having the least ability. Tilapia digested carbohydrate better than the other two species, however, whether from wheat or corn sources. The same pattern applies to the digestibility of energy.
50 citations
TL;DR: It will depend on the availability of trained husbandry personnel and on the future development of the eel market in Europe whether eelculture in north-west Europe can in the long term remain competitive with natural catches and with eel culture in the Mediterranean area.
Abstract: . World production and consumption of eels, Anguilla spp., was about 100000-110000 tonnes/year in 1987. About 70-80% of the world production is consumed in Japan. This amount is almost completely produced by eel culture in Japan and Taiwan. The remaining 20-30% of the world production is consumed in Europe. About 15% of Ihe European eel market, i.e. 3000-4000 tonnes/year, is covered by cultured eels.
In this review a description is given of the history and present status of eel culture in Japan and Europe. The economical comparison between eel culture in Japan and Europe shows much higher levels of both production costs and sales prices in Japan. Uncertainty about the future price developments and competition within Japan and with Taiwan (and China) keep a constant pressure on Japanese eel farmers to optimize their production process. Although a further optimization of the recirculation systems in north-west Europe is also needed, it will depend on the availability of trained husbandry personnel and on the future development of the eel market in Europe whether eel culture in north-west Europe can in the long term remain competitive with natural catches and with eel culture in the Mediterranean area.
48 citations
TL;DR: In coastal ecosystems where freshwater input is a very important factor, gametogenesis may be affected if clams are exposed to low salinities (less than 15%) for prolonged periods.
Abstract: . Aspects of gametogenesis of the carpet-shell clam, Ruditapes decussatus (L.), in two lagoons on the Atlantic coast of north Morocco were studied during December 1986 to February 1988. The clams sampled did not show any sign of hermaphroditism and the percentage of males was 42%. The gonads started developing in mid-winter and were ripe in spring. Successive spawnings and reconstitution of gametes look place simultaneously starting from May up to the end of September. Two major spawning periods were noticed: a partial one in May-June and a complete spawning in August-September. From October to December the gonads were at resting stages. In coastal ecosystems where freshwater input is a very important factor, gametogenesis may be affected if clams are exposed to low salinities (less than 15%) for prolonged periods.
43 citations
TL;DR: Analysis of the gut contents of fish caught on powan spawning grounds in Loch Lomond showed that they, as well as native brown trout, Salmo trutta L., and powan themselves, prey upon powan ova.
Abstract: . Loch Lomond, one of the few British strongholds of the powan, Coregonus lavaretus (L.), has recently been colonized by the ruffe, Gymnocephalus cernuus (L.). The ruffe are now widespread, abundant and one of the commonest fish in Loch Lomond. Analysis of the gut contents of these fish caught on powan spawning grounds in Loch Lomond showed that they, as well as native brown trout, Salmo trutta L., and powan themselves, prey upon powan ova. Ruffe maintained a high winter feeding rate compared with powan and trout and fed on a broad range of benthic prey, of which powan ova formed the greatest biomass (84% of total diet) and dominated the diet numerically (57% of prey items). The observed incidence of powan ova consumption by ruffe was significantly greater than that of both brown trout and powan (P <0·001).
36 citations
TL;DR: A study was conducted to determine if hatchery-reared and wild barramundi, Lates calcarifer (Bloch), could be distinguished by the patterns of circuli spacing on the scales, and it has considerably more potential for evaluating the efficacy of large-scale enhancement programmes than do traditional physical tagging techniques.
Abstract: A study was conducted to determine if hatchery-reared and wild barramundi, Lates calcarifer (Bloch), could be distinguished by the patterns of circuli spacing on the scales. Proprietary software and digitizing equipment was used to obtain measurements of circuli spacing within one millimetre of the focus of the scales. Discriminant analyses separated the groups with up to 83% accuracy. As the technique utilizes innate tags laid down in response to the rearing environment, it has considerably more potential for evaluating the efficacy of large-scale enhancement programmes than do traditional physical tagging techniques.
28 citations
TL;DR: Larger fish survived better during the challenges than did smaller fish, and there was a negative genetic correlation (based on dam variance components) between body weight and mortality.
Abstract: . Chinook salmon, Oncorhynchus tshawytscha (Walbaum), from a northern streamtype (Bear River) and a southern ocean-type (Robertson Creek) population in British Columbia were mated within populations in a nested breeding design and the resulting juveniles were challenged with high water temperatures. Juveniles in the southern population died significantly later than those in the northern population, but none of the variation among families in mortality rate or time to death in the southern population was attributable to additive genetic variation. Non-additive genetic or maternal effects or both were observed for mortality rates in the Robertson Creek population, whereas additive genetic effects were observed for mortality at temperatures less than 22°C in the Bear River population. Larger fish survived better during the challenges than did smaller fish, and there was a negative genetic correlation (based on dam variance components) between body weight and mortality.
TL;DR: During weed-cutting operations on the River Frome, Dorset, England, cut weed, together with associated macroinvertebrates, was removed at five boom sites down the river because of rapid changes in the density and position of invertebrate populations, the immense sampling effort required and the non-synchronous system of cutting.
Abstract: . During weed-cutting operations on the River Frome, Dorset, England, cut weed (800t), together with associated macroinvertebrates, was removed at five boom sites down the river. The mean density of macroinvertebrates removed was 30 individuals per g dry weight of cut weed which was equivalent to 6mg dry weight per g of cut weed, ca. 4900 individuals per square metre of river bed, or 0.9g dry wt/m2 of river bed.
The cut weed removed was populated chiefly by larvae of Chironomidae and Simuliidae although the numbers and biomass of Ephemerella ignita Poda and Brachycentrus subnubilus Curtis were a significant part of the total macroinvertebrate population.
Macroinvertebrates removed on cut weed were estimated as ca. 20% by number and ca. 12% by biomass of the total population from published values. The river (50km) was difficult to sample immediately prior to weed cutting because of rapid changes in the density and position of invertebrate populations, the immense sampling effort required and the non-synchronous system of cutting.
TL;DR: Production of Florida red tilapia seed in above-ground tanks using recirculated brackishwater was studied, indicating the advantages of replacing broodstock with yearling breeders each year.
Abstract: . Production of Florida red tilapia seed (eggs, sacfry and fry) in 34-m2 above-ground tanks using recirculated brackishwater (12 ppt) was studied over a 5-month period on Lee Stocking Island (Exuma Cays, Bahamas). Four tanks were stocked with year class 1 (YCI) breeders, while 2 tanks were stocked with year class 2 (YCII) breeders at densities of 200 and 240/tank (5·9 and 7·1/m2), respectively, and at a sex ratio of 3 females to 1 male, beginning in November 1988. Seed production was measured by removing free-swimming fry from tanks and eggs and sacfry from the mouths of brooding females, and assessing the number of each at 15 to 16-day intervals from February to June 1989. Average seed production (seed/m2/day) was significantly higher in YCI (52·3) than in YCII (36·0) broodstock, indicating the advantages of replacing broodstock with yearling breeders each year.
TL;DR: Dorsal fin condition was evaluated in two groups of hatchery-reared steelhead trout, Oncorhynchus mykiss(Walbaum), and compared to wild fish to determine differences in dorsal fin condition between these groups and to monitor the progression and severity of fin damage.
Abstract: . Dorsal fin condition was evaluated in two groups of hatchery-reared steelhead trout, Oncorhynchus mykiss(Walbaum), and compared to wild fish. Hatchery fish were reared either in nursery tanks with baffles or in isolation (1 fish/rearing space). Evaluations were conducted to determine differences in dorsal fin condition between these groups and to monitor the progression and severity of fin damage. Isolated hatchery and wild steelhead trout maintained perfect dorsal fins with characteristic white margins. Hatchery fish reared in nursery tanks with baffles experienced dorsal fin erosion that started when the fish were about 40mm total length (30 days after being on feed). This erosion continued until dorsal fin length averaged only 2·3 mm in fish 161–200 mm total length in contrast to an average dorsal fin length of 20·9mm in wild fish of the same size.
TL;DR: If the smalt nutrient-film hydroponic technique hydroponics unit was incorporated into the aquarium filter system as a single passage unit, water quality could be maintained, together with the production of a useful crop.
Abstract: . The feasibility of using a smalt nutrient-film hydroponic technique hydroponics unit as a mineral filter for a recirculating aquarium system has been Investigated. The aquarium in question employed microbial biofilters to convert ammonia and waste materials to a mineralized form, particularly nitrates.
A recirculating NFT system was designed using a 40-l capacity catchment refilled at weekly intervals from the aquarium, which was stocked with common carp, Cyprinus carpio L. and rainbow trout, Oncorhynchus mykiss (Walbaum). Four crop species were grown (garden peas, Pisum sativum L., lettuce, Lactuca sativa L., watercress. Nasturtium officinale R., and barley, Hordeum vulgare L.) with no additional nutrient supply. A control system was set up using tap water. Although yields were not as high as seen in commercial NFT systems the aquarium water-fed system produced viable plants, with higher yields and better quality than seen in the controls. At the same time mineral levels, especially nitrates, were reduced.
If the unit was incorporated into the aquarium filter system as a single passage unit, water quality could be maintained, together with the production of a useful crop. The data obtained in the present study are compared with previous reports on the use of hydroponics in conjunction with fish culture.
TL;DR: Overall results can be greatly improved by initiating the feeding behaviour of the fish by feeding cod roe for the first few days and a strong effect of the feeding level on feed acceptance is demonstrated.
Abstract: . In four experiments, performed at the Agricultural University, Wageningen and the Netherlands Institute for Fishery Investigations, the effects of attractants on feed acceptance and growth of glass eels, Anguilla anguilla L., were studied. The results show that extracts from natural food or a mixture of synthetic amino acids improve acceptance of a trout fry crumble at first feeding of glass eels. Overall results can be greatly improved by initiating the feeding behaviour of the fish by feeding cod roe for the first few days. The results also demonstrate a strong effect of the feeding level on feed acceptance. At relatively high feeding levels no significant effect of attractants could be detected.
TL;DR: A 156-day cage feeding trial was conducted with fingerling seabass, Lates calcarifer (Bloch), and grouper, Epinephelus tauvina (Forskal), so as to test six different dietary feeding regimes and the results are analysed from an economical viewpoint and discussed on the basis of other published studies.
Abstract: . A 156-day cage feeding trial was conducted with fingerling seabass, Lates calcarifer (Bloch), and grouper, Epinephelus tauvina (Forskal), so as to test six different dietary feeding regimes, namely no exogenous feeding (NF), frozen fish (FF), commercial shrimp finisher pellet (SP), in-house prepared dry pellet RDI (RDI) and RD2 (RD2), and an in-house prepared moist pellet (frozen fish: diet Rd1, 40:60 mixture w/w — code MP). Seabass fed FF and MP displayed the best growth response, with fish (30/m3) growing from an initial weight of 8·9g and 8·5g to a final weight of 285·5g and 257·5 g in 156 days, with a food conversion ratio of 3·77–5·10 (dry matter basis 1·15 – 1·95), and with a survival of 93·3 and 93·3% respectively. Similarly, grouper fed FF and MP also displayed the best growth response, with fish (30/m3) growing from an initial weight of 23·8 g and 25·8g to a final weight of 471·7g and 388·7g in 156 days, with a food conversion ratio of 3·53–4·16 (dry matter basis 0·89–1·06) and 1·73–2·96 (dry matter basis 1·06–1·80), and with a survival of 90 and 98·3% respectively. The results are analysed from an economical viewpoint and discussed on the basis of other published studies.
TL;DR: The results suggest that the Cadiz and Tinamenor stocks are reproductively isolated and show a level of stock differentiation not previously known in populations of this species.
Abstract: . One hundred specimens of the European seabass. Dicentrarchus labrax L., from a natural population (Cadiz, Spain) were analysed by starch gel electrophoresis for 23 enzymes; 49 loci were identified, of which five were polymorphic (ADH*, AAT-3*, EST-.3*, MEP-1* and SOD-2*) P = 10·2% and HQ = 1·8%. Twenty specimens from a hatchery at Tinamenor in northern Spain (Fl progeny from wild) were analysed for 28 different enzymes. A total of 61 loci were identified of which 4 were polymorphic (LDH-1*, LDH-2*, MEP-1*, and XDH-2*) P = 6·6%,Ho= 1·5%. A total of 31 enzyme systems and 79 different loci were analysed in the two populations. The results suggest that the Cadiz and Tinamenor stocks are reproductively isolated and show a level of stock differentiation not previously known in populations of this species. An estimate of genetic distance based on the 31 loci compared in both populations gave a value of D=0·012+0·018 and a genetic similarity of I=0·988. The implications of these results for fisheries and aquaculture are briefly discussed.
TL;DR: By using satiation feeding, marketable size rainbow trout can be produced in temperate region ponds without increases in percentage body fat or feed conversion ratio (FCR).
Abstract: . In temperate regions of North America, the culture of rainbow trout, Oncorhynchus mykiss (Walbaum), in ponds is constrained to the period mid-November to early April by water temperature. Feeding practice may influence production time. The effects of three feeding practices on growth and body composition of rainbow trout raised in ponds during a 142-day winter growth period were investigated. Feeding practices were (1) hand-feeding to satiation, (2) feeding according to a fish size/water temperature chart, and (3) feeding by demand feeder.
Fish fed to satiation consumed 66% more diet than fish fed according to a feeding chart and 163% more than fish fed by demand feeders. Fish fed to satiation had significantly higher (P 0·05) in percentage body fat or feed conversion ratio (FCR) compared to the other two treatments. Survival percentage did not differ significantly (P > 0·05) between treatments. These data indicate that by using satiation feeding, marketable size rainbow trout can be produced in temperate region ponds without increases in percentage body fat or FCR.
TL;DR: There was some evidence that growth variability of the largest lobsters was influenced by the size of the rearing compartments used during the final growth period.
Abstract: Information on carapace length (CL) and its variability at each instar from settlement (instar 4) to pre-recruit size (instar 24) is presented for 10 individually reared single parent broods and one mixed brood of European lobster, Homarus gammarus (L) The lobsters grew from 5mm CL to 74mm CL in approximately 130 weeks at 20°± 2°C There was some evidence that growth variability of the largest lobsters was influenced by the size of the rearing compartments used during the final growth period
TL;DR: Fecundity was found to vary from 1216 to 89747 eggs for prawns measuring 9.0cm to 15.8cm total length, and the increase in the weight of the grey eggs can be explained by the elongation of fully formed organs and appendages by about 17 days post fertilization.
Abstract: . For a study of the fecundity of Macrobrachium rosenbergii, a total of 117 berried females were sampled from ponds. Fecundity was found to vary from 1216 to 89747 eggs for prawns measuring 9.0cm to 15.8cm total length and weighing 6.22 to 45.80g. The relationship between fecundity (EN) and total length (TL) was found to be EN = 0.001876 TL6.3617.
The average egg number/g total body weight for prawns having orange, yellow and grey eggs was 1132.7 ± 484.1,766.4 ± 524.3 and 745.5 ± 487.2, respectively, a decrease of 32.3% when orange eggs became yellow and 34.3% when they turned grey. This decrease was probably due to unfertilized eggs dropping off and some eggs being eaten by the brooders during the incubation period.
Egg numbers/g egg weight were found to be 11360.1 ± 1642.1,10715.7 ± 2725.3 and 8634.0 ± 1892.3 for orange, yellow and grey eggs, respectively. When compared to orange eggs, yellow eggs were slightly heavier (6%), but grey eggs were significantly heavier by 31.6%. The increase in the weight of the grey eggs can be explained by the elongation of fully formed organs and appendages by about 17 days post fertilization.
TL;DR: These trials suggest that optimal growth and FCRs were obtained at 25°C; with feed rates of 6%/day with juveniles, 2%/ day with sub-adults, and 1% /day with adult fish.
Abstract: Chinese catfish, Clarias fuscus (Lacepede), within three size ranges were evaluated for growth, survival and feed conversion ratios (FCR) A 4 × 3 factorial design was used during year-long trials which included four temperatures (20,25,30 and 35 °C) and three feeding rates with commercially formulated salmon/trout feed Specific growth rates of juvenile fish (1–60g) were highest, ranging from 1–64% body weight/day at 20°C (2%/day feed rate), to 4–94%/day at 25°C (6%/day feed rate) Specific growth rates of sub-adult fish (60–150g) averaged 0–65%/day, with no significant difference between temperature-feed rate treatments Specific growth rates of adult fish (>150g) were lowest, averaging 0–30%/day for grouped feed rate treatments at 25°C, and 0–16%/day at 30°C Most mortalities occurred during the juvenile stage, with survival ranging from 0% at 35°C(2% feed rate) to 96% at 30°C(6% feed rate) Survival was 95–100% with sub-adults and adults FCR were 1 to 4 with juveniles, 2 to 12 with sub-adults, and 3 to 22 with adults These trials suggest that optimal growth and FCRs were obtained at 25°C; with feed rates of 6%/day with juveniles, 2%/day with sub-adults, and 1%/day with adult fish Final yields at 25 and 30°C indicate that even though growth and FCR are optimal at 25°C, survival was greater at 30°C, which compensated for reduced growth performance at this temperature Yields at 25 and 30°C were almost double those at 20°C
TL;DR: The‘maximum acceptable toxicant concentration’ of ammonia-N and NH3-N for P. monodon post-larvae was 0·60mg/l and 32μg/l, respectively after 6 weeks of exposure, which is higher than the previous results obtained for tiger shrimp exposed to control.
Abstract: . Tiger shrimp, Penaeus monodon Fabricius, post-larvae (32·0±3mg, 1·43±0·03 cm) were exposed to control, 0·12, 0·60, 1·20 and 2·40mg/l ammonia-N (un-ionized plus ionized ammonia as nitrogen) which is equivalent to control, 6,32,63 and 126μg/1 NH3-N (un-ionized ammonia as nitrogen) for 8 weeks in 25 ppt, as pH of 7·85–8·18 and 26–28°C by static renewal method. Growth in weight and length of the shrimps exposed to 1·20 and 2·40 mg/l ammonia-N were significantly lower (P < 0·05) than those exposed to control. The EC50 (concentration that reduced growth by 50% of that of the controls) was 1·33 mg/l ammonia-N, 70 μg/l NH3-N for weight gain, and 2·35 mg/1 ammonia-N, 123μg/l NH3-N for length gain of P. monodon post-larvae. The‘maximum acceptable toxicant concentration’(MATC) of ammonia-N and NH3-N for P. monodon post-larvae was 0·60mg/l and 32μg/l, respectively after 6 weeks of exposure.
TL;DR: The male and female zander were equally exploited by anglers and the angling vulnerability of zander was negatively related with the availability of forage fish.
Abstract: . In four 0.8-ha drainable ponds the production, growth, condition and angling vulnerability of zander ( 15cm). The experiments look place in the period April-October 1986. The P:Bu ratios of zander in two ponds with an average biomass of forage fish (282 kg) 3.5 times the mean biomass of zander(.80kg), were 0.17 and 0.28. In two ponds with an average biomass of forage fish (38kg) 0.58 times the mean biomass of zander (65 kg), P:Bu ratios were 0.02 and 0.06. The growth and condition responses of individual zander were highly variable within each pond. Effects of sex were not observed on these responses. In June 1986 the angling vulnerability of zander was negatively related with the availability of forage fish. In August-September 1986 no differences in angling vulnerability were observed between the zander in the four ponds. The male and female zander were equally exploited by anglers. The captures of zander were not related with the size or weight of the fish.
TL;DR: It is demonstrated that supersaturated total gas pressure due to excessive oxygen saturation causes gas bubble disease in the absence of supersaturated nitrogen gas and it is recommended that users of oxygen injection systems closely adjust the amount of oxygen added to the water to keep thetotal gas pressure near saturation.
Abstract: . An Aquatector oxygen injection unit was used to supersaturate a hatchery water supply to 200% oxygen saturation (18–20mg/l) and increase the total gas pressure to 120% of saturation. Nitrogen saturation was reduced to near 100%. Rainbow trout, Oncorhynchus mykiss (Walbaum), held in the treated water developed signs of gas bubble disease in 4 days, and 50% died within 20 days. We demonstrated that supersaturated total gas pressure due to excessive oxygen saturation causes gas bubble disease in the absence of supersaturated nitrogen gas. It is recommended that users of oxygen injection systems closely adjust the amount of oxygen added to the water to keep the total gas pressure near saturation.
TL;DR: It is concluded that the main physicochemical factors responsible for the spatial distribution of fish populations were low concentrations of dissolved oxygen for trout and the siltation of SIM for cobitids, the increased fluoride concentration being a minor factor.
Abstract: . The influence of an industrial effluent on the spatial distribution of fish populations in the regulated Rio Duraton (northern Spain) was examined by field and laboratory studies. The effluent caused an increase in the fluoride ion concentration at three downstream sampling sites (mean values 6·8, 2·7 and 1·3mg/l) compared with reference stations (0·1 mg/l). The suspended inorganic matter (SIM) only increased immediately below the effluent, settling on the stream bottom of this sampling station. In addition, hypolimnial waters with low concentrations of dissolved oxygen (<5 mg/l) were released daily by the dam. Rainbow trout, Oncorhynchus mykiss (Walbaum), and brown trout, Salmo trutta L., disappeared downstream of the impoundment. The 72 and 96h LC50s (mgF-/1) calculated from fluoride toxicity tests in soft water were 138·5 and 107·5 for rainbow trout, and 223·0 and 164·5 for brown trout. Fish (Barbus bocagei Steindachner, Rutilus arcasii (Steindachner) and Gobio gobio (L.)) were collected at all sampling stations. The benthic fish species Cobitis maroccana Pellegrin was also collected downstream of the impoundment but was absent just below the industrial effluent. It is concluded that the main physicochemical factors responsible for the spatial distribution of fish populations were low concentrations of dissolved oxygen for trout and the siltation of SIM for cobitids, the increased fluoride concentration being a minor factor.
TL;DR: The results confirm those of Risch (1986a), who, using morphological data, considered the two taxa to be synonyms, and several of them being monomorphic at the 19 loci studied.
Abstract: Thirteen populations of Chrysichthys auratus long@lis (Pfaff) and C. filamentosus (Boulenger) from five West African drainages were studied using enzymatic protein electrophoresis to estimate genetic differentiation and verify their taxonomic status. Twenty- seven alleles were observed at 19 loci. Only five loci were polymorphic. Genetic distance and cladistical analyses based on presenceslabsences of alleles did not separate the populations in groups corresponding to the two taxa. The maximum genetic distances between two populations (D = 0.112) is lower than the level of maximum divergence observed between conspecific populations of species of the genus in other studies using the same enzymatic systems (D = 0.289 in C. maurus; D = 0.304 in C. nigrodigitatus). These results confirm those of Risch (1986a) who, using morphological data, considered the two taxa to be synonyms. Genetic variability in several of these populations is also low (0-00 < H < 0.064)' some of them being monomorphic at the 19 loci studied. The reasons for this low variability are discussed.