Production of the Malawi chambo, Oreochromis karongae (Trewavas, 1941) association, and Oreochromis shiranus (Boulenger, 1896) in polyculture with the African catfish, Clarias gariepinus (Burchell, 1822)

Results are reported of the growth and yield of the Malawi chambo, Oreochromis karongae (Trewavas, 1941) association, and Oreochromis shiranus (Boulenger. 1896) in polyculture with Clarias gariepinus (Burchell. 1822). Six ponds of 150 m² were assigned to two replicates of three treatments: C. gariepinus and O. shiranus; C. gariepinus and chambo spawned on station; C. gariepinus and chambo collected from the lake. Total fish stocking density was 3 m^?2, and stocking ratio 1:2 (C. gariepinus: titapias). Initial mean body weights were 10.9 g for O. shiranus. 13.2 g for C. gariepinus and 13.3 g for chambo. The ponds were fertilized with chicken manure at the rate of 13.5 kg dry matter ha^?1 day^?1, representing the daily NPK loading of 0.618.0.186 and 0.191 kg ha^?1, respectively. Maize bran was applied at 3% body weight day^?1 for 168 days. Fish growth rate for C. gariepinus was significantly higher (P < 0.05) than that of the tilapias. Weight gains were 0.48-0.57 g day^?1 for C. gariepinus, 0.30-0.31 g day^?1 for chambo and 0.24 g day^?1 for O shiranus. There was no difference (P > 0.05) in the growth of chambo despite the source of fingerlings. More fish biomass came from C. gariepinus stocked at 1 m^?2 than from the tilapias stocked at 2 m^?2. Extrapolated fish yields in the range of 4.37-4.75 t ha^?1 year^?1 were obtained from the polyculture of chambo and C. gariepinus. Oreochromis shiranus and C. gariepinus gave 3.95 t ha^?1 year^?1. Low water temperatures for 112 days slowed the growth of tilapias but did not seem to inhibit the growth of C. gariepinus. Chicken manure and maize bran, applied at smallholder farmer's level, has produced higher yields than by using O. shiranus in monoculture at optimal temperatures. The yields obtained show that the polyculture system is feasible during the cold season and may justify investment in aquaculture at semi-intensive level in Malawi.     

温度对虾夷扇贝幼体和稚贝生长,成活率的影响

在１５．０℃、１７．５℃和１９．０℃３个温度梯度下，各试验组纪体的生长速度和成活率６．３μｍ／ｄ，８．６μｍ／ｄ、９．３μｍ／ｄ；６１．０％、７０．５％、２３．０％。投附着基经２２ｄ培养各试验组稚贝规格（壳长×壳高）分别平均为６２０μｍ×５９５μｍ、７０５μｍ×６８０μｍ、７４５μｍ×７１０μｍ；各组生长速度和附着后成活率分别为１７．７μｍ／ｄ、２１．６μｍ／ｄ、２３．４μｍ／ｄ；３５．４％、３４     

Digenean (Bucephalidae) infections in commercial scallops, Pecten fumatus Reeve, and doughboy scallops, Chlamys (Mimachlamys) asperrima (Lamarck), in Jervis Bay, New South Wales

Sympatric populations of the hermaphroditic scallop, Pecten fumatus Reeve, and of the dioecious scallop, Chlamys (Mimachlamys) asperrima (Lamarck), from Jervis Bay, New South Wales, Australia, were sampled between October 1991 and December 1994. Over the first 2 years, 5.1% of adult P. fumatus and 4.5% of adult C. asperrima were infected with a trematode, Bucephalus sp., that causes parasitic castration. A significant increase in the numbers of infected scallops occurred in spring 1993, teaching 63% in P. fumatus and 24% in C asperrima in May and March 1994, respectively. The prevalence of infection increased with scallop size, reaching 66% in P. fumatus greater than 80 mm in shell height and 40% in C. asperrima greater than 75 mm in 1994. Seasonal and interannual variations in parasitism for the P. fumatus recorded over a continuous period of 5 years in Jervis Bay are discussed, as are interspecies differences and the potential impact of the parasitic castration on reproductive potential and marketability of P. fumatus and C. asperrima.     

Infection of tilapia, Oreochromis mossambicus (Trewavas), by a marine monogenean, Neobenedenia melleni (MacCallum, 1927) Yamaguti, 1963 in Kaneohe Bay, Hawaii, USA, and its treatment

Abstract A disease of saltwater, cage-cultured tilapia, Oreochromis mossambicus (Trewavas), caused by the marine monogenean, Neobenedenia melleni (MacCallum, 1927) Yamaguti, 1963, is described. Up to 400 parasites were found attached to the body surface of individual fish. Heavily infected fish showed hyperirritability, heavy mucus secretion and discoloration. Pathology was most marked on the eye, with corneal opacity initially, followed by buphthalmos, corneal ulceration and rupture of the eye with subsequent degeneration of internal structure. The infection was successfully treated using 2 min freshwater dips.     

Preferred temperature of grass carp, Ctenopharyngodon idella (Valenciennes), and brema carp, Megalobrama amblycephala (Yih), (Pisces, Cyprinidae) in horizontal and vertical gradients

The preferred temperatures of grass carp, Ctenopharyngodon idella (Valenciennes), and brema carp, Megalobrama amblycephala (Yih), were determined individually and together in both horizontal and vertical gradients. No significant difference was found by two methods between the preferred temperatures in either species of carp (28.0-28.5 ^oC) when the fish were placed individually. However, when the two species of carp were placed together, C. idella was displaced thermally, preferring a temperature of 23.5 ^oC, which was significantly lower than that obtained when it was held separately. This suggests that, if both species of carp are placed in ponds forming part of a Chinese polyculture system, C. idella will seek out a lower temperature as a mechanism to avoid competition, and therefore, the growth of this species will be reduced.     

A note on the hybrid mrigal,Cirrhinus mrigala (Hamilton) × common carp,Cyprinus carpio (Linnaeus) (Cyprinidae)

Mrigal-common carp hybrids were produced and examined. Only few hybrids could be reared up to the age of 14 months. These did not show signs of maturity. The parents species mature in ponds in 6 months (common carp) or 12 months (mrigal).     

Experimental co-culture of low food-chain organisms, Sabella spallanzanii (Polychaeta, Sabellidae) and Cladophora prolifera (Chlorophyta, Cladophorales), in Porto Cesareo area (Mediterranean Sea)

The filter feeder polychaete Sabella spallanzanii (Gmelin) was co‐cultured with the green seaweed Cladophora prolifera (Roth.) Kunz, in an off‐shore experimental system. Both species have previously been experimented as bioremediator organisms for waste treatment deriving from aquaculture farms and can have a high economic value as a byproduct of polyculture. The present experiment has been conducted in an area 2 miles off the coast of Porto Cesareo (Ionian sea, Southern Italy). The growth was followed in some modules anchored to the bottom at two different depths (15 and 25 m depth). The results indicate differences among replicates located at different depths. Both organisms show a faster growth at the shallower levels. Within this level, polychaetes reached a mean biomass of 860±74 mg dw (average±SE) per worm, 30 times larger than that of the starting point, after a standstill in the first period, probably due to the manipulation activities. The major growth has been recorded during the winter. Algae have shown an increase of 34 g ww month⁻¹ (average±SE) in the shallower levels vs. only 11 g ww month⁻¹ (average±SE) in the deeper levels. The RGR calculated after 60 days was 115% in the shallower levels vs. about 60% in the deeper ones. A considerable decrease in growth rate was observed during the last period; this was probably due to the presence of increasing fouling community on the rearing cages surely affecting the light intensity.     

Loma salmonae (Putz, Hoffman and Dunbar, 1965) in the rainbow trout, Salmo gairdneri Richardson, and L. fontinalis sp. nov. (Microsporida) in the brook trout, Salvelinus fontinalis (Mitchill)

Abstract. Loma salmonae (Putz, Hoffman and Dunbar, 1965), Morrison & Sprague, 1981, in the rainbow trout, Salmo gairdneri Richardson, was studied with the electron microscope. It is morphologically very similar to L. morhua Morrison and Sprague, 1981, in the Atlantic cod, Gadus morhua L., having only minor differences. Loma sp. Morrison and Sprague, 1981, in the brook trout, Salvelinus fontinalis (Mitchill), is more like L. salmonae than the other species of Loma , but was deemed to be distinct. It was named L. fontinalis sp. nov.     

Reproductive cycle of the south American scallop Amusium laurenti (Gmelin, 1791) (Bivalvia, Pectinidae)

Amusium laurenti is a functional hermaphroditewith well differentiated male and female gonadalareas. The gonadal index varies throughout the yearwith maximum values occurring in January, March andJuly, and minimum ones in August and September. Partial spawning (with respect to the individual andthe population) occurred from January to February andMarch to May. The major spawning event coincided withthe end of the period during which bottom watertemperature increased to temperatures above 26°C(July–August). Subsequently temperature decreased to22°C, with a period of gonadal restoration andincreasing gonadal index. Histological analysis ofthe gonads correlated with the gonadal index.     

Comparing biofloc,clear-water,and hybrid nursery systems (Part I): Shrimp (Litopenaeus vannamei) production,water quality,and stable isotope dynamics

Indoor, intensive, nursery-based recirculating aquaculture systems (RAS) can provide high-quality juvenile shrimp for indoor or pond-based production systems in a biosecure manner. However, it is unclear what type of RAS is most appropriate for indoor shrimp nurseries. This study compared three types of RAS nurseries: biofloc (BF), clear-water (CW), and hybrid (HY). Each treatment included four, randomly assigned 160 L (0.35-m²) tanks that were stocked with 3000 post-larvae shrimp m⁻³. The post-larvae (PL10) shrimp had an initial average weight of 7 ± 0.0 mg and were grown for 48 days. The BF tanks included external settling chambers as the only filtration mechanism. The CW tanks had settling chambers, foam fractionators, and external biofilters to fully clarify the water and process nitrogenous waste. Hybrid tanks included settling chambers, and external biofilters to maintain some suspended solids along with external biofiltration. Overall, the CW treatment had significantly higher dissolved oxygen (DO) and pH levels than the BF and HY systems. The HY treatment had significantly higher DO than the BF treatment. Nitrite concentration was significantly higher in the HY treatment than the CW treatment. Turbidity in the BF treatment was significantly higher than the other treatments. On the final sample date, the BF treatment had significantly higher nitrite and nitrate concentrations than the other treatments. Differences between treatments in terms of shrimp survival, mean harvest weight, specific growth rate, and feed conversion ratio were not significant. The final weight of the shrimp at 48 days for the BF, CW, and HY were 670 mg, 640 mg, and 590 mg respectively. A stable isotope mixing model indicated that, in the BF treatment, 13% of the C and 34% of the N in harvested shrimp tissue may have originated from biofloc material, signifying some nutrient recycling. The nitrification process was more effective with the inclusion of an external biofilter. All three system types appear suitable for RAS shrimp nursery production although consideration should be given to water quality consistency and filtration costs.     

Powan, Coregonus lavaretus (L.), ova predation by newly introduced ruffe, Gymnocephalus cernuus (L.), in Loch Lomond, Scotland

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).     

Pharmacological treatments against Ichthyobodo necator (Henneguy, 1883) in rainbow trout, Oncorhynchus mykiss (Walbaum)

Abstract. Various antiparasitic drugs belonging to several pharmacological groups were tested by bath administration for in vivo activity against a natural infestation of rainbow trout. Oncorhynchus mykiss (Walbaum), by he flagellate protozoan Ichthyobodo necator. Fish were also monitored for signs of drug toxicity. Complete elimination of infestation in all fish was achieved only by bithionol (25 mgl^-1 for 3h on two consecutive days). Ketoconazole, toltrazuril, amprolium, sulphaquinoxaline, quinacrine, N-metylglucamine, chloroquine, 1,3-di-6-quinolylurea, diminazene aceturate and paromomycin were not effective. Diminazene aceturate (100 mgl^-1, 3h) was the only drug which was clearly toxic. The comparison of the response of symptomatic and asymptomatic infested fish to a formaldehyde bath indicates that poor health caused by I. necator may greatly increase the susceptibility of fish to the toxic effects of a drug or chemical.     

Morphology,seasonality and phylogeny of Zschokkella soleae sp. n. (Myxozoa,Myxosporea) parasite of Solea solea (L.) (Pleuronectiformes,Soleidae) from Ghar El Melh Lagoon,Tunisia

A new Myxosporea, Zschokkella soleae sp. n., was found in the gall bladder and the bile of common sole, Solea solea (L.), from Ghar El Melh Lagoon in north‐east Tunisia. This is the first record for the presence of Zschokkella species in Tunisian waters. The parasite's plasmodia are polysporic with variable size and shape. Some plasmodia appeared attached to the gall bladder epithelium while others were found free in bile. Mature spores are ellipsoidal in frontal view 13.8 ± 0.38 μm long and 10.86 ± 0.40 μm wide with two equal size spherical polar capsules 3.6 ± 0.43 μm in size. The prevalence of infection seems to correlate with host size and changes over the year with maximum percentage in summer. Based on the 18S rDNA sequence data, Z. soleae sp. n. is readily distinguishable from other myxozoan DNA sequences in GenBank. Phylogenetically, the new species is placed in the freshwater Myxidium clade including several Zschokkella spp. infecting the gall bladder. Morphology, histology as well as DNA sequence analysis indicate that the examined species differs from all previously described Zschokkella species.     

Presence of Anisakis simplex (Rudolphi, 1809 det. Krabbe, 1878) and Hysterothylacium aduncum (Rudolphi, 1802) (Nematoda; Anisakidae) in runts of farmed Atlantic salmon,Salmo salar L

One hundred farmed Atlantic salmon, Salmo salar L., were examined for the presence of nematodes by digestion of tissue in HCl–pepsin solution. All fish were sampled from one cage in a fish farm on the Norwegian south‐west coast. Fifty harvest quality salmon, that is, salmon for human consumption (mean 5.4 kg, variation 3.0–7.6 kg), were sampled at the processing line while 50 salmon runts (mean 1.1 kg, variation 0.4–1.8 kg), discarded due to poor performance, were sampled from the discard bin after the grading station. Runts are individual fish with clear signs of poor performance over time and abnormal appearance and are thus not processed for human consumption. No nematodes were found in the musculature or viscera of the 50 harvest quality salmon. In total, 75 nematodes were found in 10 (20%) of the runts; 53 nematodes in the viscera and 22 in the musculature. Nematodes in the musculature were identified as Anisakis simplex (Rudolphi, 1809 det. Krabbe, 1878), while nematodes in the viscera were identified as A. simplex and Hysterothylacium aduncum (Rudolphi, 1802).     

Mobilization of organic reserves during ovarian development in a marine penaeid prawn,Parapenaeopsis hardwickii (Miers) (Crustacea,Decapoda, Penaeidae)

The present study furnishes data concerning changes in biochemical constituents of midgut gland and ovary of Parapenaeopsis hardwickii associated with ovarian development. The ovarian index (0I) increased as the ovary developed from stage I (0I = 2.80 ± 0.32) to stage IV (0I = 5.85 ± 0.38) and then decreased suddenly in stage V (0I = 1.20 ± 0.45) following spawning. Associated biochemical parameters (protein, glycogen and fat) show remarkable variation. There was a continuous decline in these parameters in the midgut gland during ovarian development and a similar increase in their concentration in the ovary. The physiological significance of these findings is discussed briefly.