Increasing Fish Weight Research Articles

Assessment of Heavy Metals Concentration in Water and Fish of Dalmaj Marsh, Iraq

Most marshes in Iraq face several challenges as aquatic environments, including pollution by various chemical agents and heavy metals. The current study deal with an analysis of the water quality of Dalmaj marsh as one of the closed aquatic environments in the middle parts of Iraq located between latitudes 32ᵒ 05′ to 32ᵒ 23′N and longitudes 45ᵒ 10′ to 45ᵒ 38′ E. The marsh is suffering from a shortage in water supply, especially during the summer. It will lead to a concentration of heavy metals that are washed and transported to the marsh from the surrounding watersheds through surface runoff. This work aims to analyze water and fish samples to assess heavy metals and their accumulated risk in fish tissues based on many indices. The 16 samples of water and nine samples of fish are collected and analyzed for concentration of heavy metals, i.e., Lead (Pb), Chromium (Cr), Nickel (Ni), Cadmium (Cd), Copper (Cu), Zinc (Zn). The water analysis results indicate that Chromium (Cr) only comes below the permissible limit in water. At the same time, the composite heavy metals pollution index (HPI) identified that the water samples are varied from light pollution to malignant pollution. Regarding fish samples, three indices, i.e., BAF, EDI, and HI, are used to test the accumulated concentration of heavy metals in fish tissues and to point out their risk to consumers. The results indicate that Pb and Ni are the more hazardous metals accumulated in many fish samples with increasing fish weight, while hazard index (HI) is an additive index of all tested heavy metals, indicating concern risk from most fish samples. The study recommends testing the marsh water pollution periodically.

Kinerja Produksi Ikan Lele (Clarias gariepinus sp) dengan Ukuran Tebar Berbeda Pada Sistem Akuaponik

Catfish (Clarias gariepinus Burchell, 1822) is a type of freshwater fish that is prospectively cultivated. This study aims to analyze the production performance and economic analysis of catfish on aquaponics technology with floating raft systems. This research was conducted descriptively with two treatments and four replications. The treatments included fish sizes, which were 6-9 cm (A) and 3-4 cm (B). The fish used were fish with an initial weight of 7.13±1.30 g and 4.11±0.43 g, the plant used was water spinach (Ipomoea reptans poir) with an initial height of 8-10 cm. The results showed that there was a trend of increasing fish weight during the study from 7.13±1.30 g and 4.11±0.43 g to 110.02±6.09 g and 86.44±5.00 g at the end of the study. . The survival rate value during the study was 100% for all treatments, the feed conversion value ranged from 1.48-1.59. The highest specific weight growth rate was 1.60%/day. Water spinach production during catfish rearing can be done for 3 harvests. The analysis of the aquaponics business of the floating raft system is very efficient and profitable. The value of R/C ratio > 1 in all treatments means that the cultivation business is said to be feasible. Payback period of 0.57 years (A) and 0.19 years (B), the fastest return on investment is in treatment B. Aquaponics floating raft system with catfish stocking size 3-4 cm for 60 days of maintenance period provides the best production performance with SR value was 60.78%, specific weight growth rate was 0.051%/day, feed conversion was 1.18 and the best kale production was 75 kg. Economically, this research is feasible to do.

Research Article: Optimum weight of stellate sturgeon (Acipenser stellatus) fingerling to release into brackish water: plasma electrolytes, plasma hormones and histological observation

The present study was conducted to determine the appropriate weight to release the hatchery produced fingerling of stellate sturgeon, Acipenser stellatus, into its natural habitat. For this purpose, prolactin and cortisol hormones, plasma electrolytes and osmolality as well as histological changes in the gill and kidney of stellate sturgeon transferred from fresh to brackish water at different weight (0.5, 1, 2, and 3 g) were assessed during a one-week time course. A total of 2400 fingerlings with different weights (0.5, 1, 2, and 3 g) were equally assigned into 24 aquariums, each one containing 200 L of freshwater or brackish water. After 24 hours, prolactin showed the highest concentration in 0.5 and 3 g fish groups kept in both experimental waters. Cortisol exhibited a time-dependent increase in the 0.5 g group in both experimental waters as well as the 2 g larvae kept in the brackish water. Generally, lower levels of Mg2+, Ca+2; K+, Na+, and Cl- were measured in the fish kept in freshwater aquariums. The lowest levels of osmolarity were found in the 0.5 g fingerling, especially those kept in the freshwater aquariums, whereas the highest levels were observed in 3 g groups in both experimental waters. Histological assessments illustrated that the volume of chloride cells in freshwater increased with increasing fish weight, whereas the cell count decreased. The same held true for glomerular capillary network size. Taken together, the evidence from this study suggests that stellate sturgeon fingerling less than 2 g are almost incapable to be transferred to brackish and saline environment, due to lack of kidney and gill development.

A novel paper-based and pH-sensitive intelligent detector in meat and seafood packaging

The annual amount of food waste or loss is about one-third of the total edible food globally produced for human consumption. Continuous and real-time monitoring by spoilage detectors can significantly reduce food waste. A novel paper-based pH-sensitive meat spoilage detector was developed. A mixture of soybean hulls (SBHs) (hydrothermally-treated in an acidic environment), bentonite, and bromocresol purple (BCP) was coated on paper to produce the detector. The resultant meat spoilage detector was evaluated as a real-time freshness and spoilage indicator of catfish fillets (Ictalurus punctatus). Freshness and spoilage of fish meat with varying weights and headspace were determined by tailoring the detector's pH. Elemental, structural, and functional analysis verified the formation of a packed SBH-bentonite matrix with enhanced gas adsorption capacity and effective BCP-immobilization. Binder nanofibrillation increased the overall visual color vibrancy and decreased the binder demand in the coating formulation. Headspace volume in the studied range (40 and 160 cm3) did not affect the activation time of the detectors. However, increasing fish weight decreased the detectors' optimum activation time and pH. The findings of this study show that the developed detectors can be tailored for a wide range of sample and packaging sizes by simply adjusting the pH of the detector.

Impacts of the Samarco Tailing Dam Collapse on Metals and Arsenic Concentration in Freshwater Fish Muscle from Doce River, Southeastern Brazil.

On November 2015, Samarco tailings dam in Mariana, Minas Gerais, Brazil, collapsed, releasing 62 million tons of tailings that advanced through 668 km of the Doce River and adjacent floodplain. Although the collapse was the worst environmental disaster in Brazil, little is known about its consequences to aquatic biota. Here we evaluate the effects of the tailings mudflow on metal and As concentration in fish and how concentration correlates with water and fish characteristics. We quantified semitotal amounts of Ag, Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, and Zn in fish muscle tissue using inductively coupled plasma mass spectrometry (ICP-MS) in 255 individuals (34 species) sampled in unaffected and affected areas along the Doce River basin. Arsenic and Hg were higher in fish from affected sites, likely due to turbulent mixing of previously sedimented material by the giant tailings wave. Silver and Zn concentrations were higher in unaffected sites. Arsenic concentration in Geophagus brasiliensis decreased with increasing fish weight. Copper and Zn decreased with increasing fish weight considering the whole assembly of fish. The tailings mudflow increased water conductivity, and conductivity increased Al concentration in fish, so we expected a larger Al concentration in fishes from affected sites. However, the observed Al concentration in fishes from affected sites was lower than expected by water conductivity. Thus, the tailings mudflow reduced Al uptake or accumulation in fishes. Mercury decreased with increasing water conductivity in both unaffected and affected sites considering all species and in G. brasiliensis alone. Despite the relatively low concentration range of metals and As found in fish, fishes from sites affected by the Fe ore tailings mudflow showed higher As and Hg concentration, compared to fishes from unaffected sites. The higher As and Hg in affected sites require further detailed monitoring to ensure safeguards of human health by fishing activity along the Doce River. Integr Environ Assess Manag 2020;16:622-630. © 2020 SETAC.

Effects of fish size and route of infection on virulence of a Danish Yersinia ruckeri O1 biotype 2 strain in rainbow trout (Oncorhynchus mykiss)

The comparative virulence of Yersinia ruckeri serotype O1 biotype 2 strain 07111224 from a Danish outbreak of enteric redmouth disease in rainbow trout (Oncorhynchus mykiss) was investigated in different sizes of rainbow trout (5, 19, 25 and 52 g) using a panel of challenge methods (bath, intraperitoneal (IP) injection, anal intubation and cohabitation).The results show that Y. ruckeri 07111224 is virulent enough to successfully cause mortality in 5–52 g rainbow trout through three different infection routes (bath, IP injection and anal intubation), and strongly suggests that susceptibility to Y. ruckeri infection is dependent on fish size. Bath challenge (108 CFU/ml) caused 79% mortality in 5 g fish, while the mortality in 19–52 g fish was approximately 26%. IP injection challenges (105–106 CFU/individual) resulted in high mortalites in fish of all sizes. Anal intubation challenges (109 CFU/individual) induced 82% mortality in 5 g fish and decreased with increasing fish weight. Finally, cohabitation challenges induced 45% mortality in 5 g test fish when test fish were cohabitated 1:1 with shedder fish, while mortalities in test fish of five other challenge groups were lower (5–25%). Statistical models were fit to the data from each challenge model. The model parameter predictions suggests statistically significant effects of fish weight for bath, IP and anal intubation challenges. Furthermore, they highlight the importance of the ratio of shedders to test fish in cohabitation challenges and of the challenge doses, in particular for the IP challenge model.

Artisanal fisheries and artificial reefs on the southeast coast of Brazil: Contributions to research and management

This work aims to analyse the contribution of artificial reefs (ARs) to marine biota based on fishers’ local ecological knowledge (LEK) of the species associated with ARs. Data were collected from November 2016 to May 2017 through 60 ethnographic interviews with artisanal fishers at the northern coast of Rio de Janeiro. Local fishers use seven methods to catch fish, with trawl nets being the most frequent (32.5%, n = 41). Some fishers use more than one gear of fish equipment, allowing the capture of several species throughout the year and to alternate the target species. The fishers reported 25 species associated with the ARs, although 15 species appeared after the installation of the artificial complex. The most frequent were the sheepshead (Archosargus probatocephalus 43.3%, n = 26), black margate (Anisotremus surinamensis 41.7%, n = 25), spiny lobster (Panulirus sp. 33.3%, n = 20), caribbean spiny lobster (Panulirus argus 31.7%, n = 19), and smooth puffer (Lagocephalus laevigatus, 31.7%, n = 19). The fishers described several ecological functions of the ARs, acting as a species reproduction site (25.93%, n = 21), increasing fish weight (18.5%, n = 15), attracting fish (16.0%, n = 13) and reducing industrial fishery (8.6%, n = 7). The interviewees had consistent LEK about local marine biota, especially species associated with the ARs. They maintained a positive perception of the ARs and pointed to the need for public policies when installing new artificial structures that can increase fish stocks in the region.

English

Proximate composition of head and scales from wild and farmed Ctenopharyngodon idella of three different weight categories W1 (601-900gm), W2 (901-1200gm) and W3 (1201-1500) was studied. An increase in protein and lipid contents was noted with an increase in weight of fish but moisture contents decreased with increasing fish weight. Significant (P<0.05) differences were found among three weight categories for moisture, protein, lipids, ash and carbohydrates. Maximum moisture was noted as 54.80% in head of wild C. idella of weight category W1. Maximum protein (21.86%) and lipid (19.39%) percentages were noted in head of farmed fish of weight category W3. Maximum ash contents were observed as 6.66% in head of wild C. idella of weight category W2. Maximum carbohydrates (0.61%) were observed in head of farmed fish of W2 weight category. The wild C. idella of weight category W1 showed maximum moisture (52.07%) and maximum protein content (23.14%) in case of weight category W2. Maximum lipids (0.74%) and maximum ash content (25.77%) were recorded in framed C. idella of W2 and W1 weight categories, respectively.

Chemical composition and release rate of waste discharge from an Atlantic salmon farm with an evaluation of IMTA feasibility

The carbon (C), nitrogen (N) and phosphorus (P) compositions of salmon feed, fish and faeces were studied at a salmon farm in Badstuvika (63° 31' N, 9° 9' E) in central Norway. These data were used to estimate the release rates of wastes from 2 salmon cages and the qualities of particulate wastes as food resources for integrated multi-trophic aquaculture (IMTA). About 38% of feed C, 43% of feed N and 24% of feed P were retained as fish biomass. About 62% of feed C, 57% of feed N and 76% of feed P were lost into the environment. Around 40% of feed C was respired as CO2, and 39% of feed N and 24% of feed P were excreted as dissolved inorganic nitro- gen and phosphorus, respectively. About 19% of feed C, 15% of feed N and 44% of feed P were released as particles. The chemical composition of feed was independent of time (p > 0.05). The faecal C content increased with increasing fish weight (r 2 = 0.14, p 0.05). Our results suggested that P digestibility of feed may be 30%, but more information is still needed to reach conclusions on this. The C content of faeces was 70% of that of feed and the N content of faeces was 50% of that of feed. The P content was far higher than that of feed. The lipid, docosa- hexaenoic acid and eicosapentaenoic acid contents of faeces were comparable to those of some phytoplankton species. The results suggested that both feed and faeces are adequate food for blue mussels and sea cucumbers co-cultured with salmon, and the nutrient content may meet their nutritional requirements.

Natural Food Selectivity Changes with Weights of Nile Tilapia, Oreochromis niloticus (Linnaeus), Reared in Fertilized Earthen Ponds

This work was carried out to study the relationship between fish weight and natural food selectivity of Nile tilapia, Oreochromis niloticus (Linnaeus) reared in earthen ponds without supplementary diet and to guide the adaptation of feeding and fertilization strategies. Fish were stocked (1.5 fish/m2) in four fertilized earthen ponds (0.1 ha) for 6 months. Fifty fish were sampled monthly to estimate individual total weight and length and evaluate stomach contents. Fish specimens were categorized into different weight classes: <25 g, 25–50 g, 50–75 g, 75–100 g, and 100–125 g. Overall, the 50–75 g weight class had the highest degree of stomach fullness. The intestinal length-fish length ratio was similar across all fish weights, ranging from 2.9–3.4. Likewise, the composition of food items found in fish stomach was ranked as phytoplankton > detritus > zooplankton. Phytoplankton contribution to gut content increased with increasing fish weight, while detritus and zooplankton contribution decreased. Zooplankton never exceeded 1% of total stomach contents. Cyanobacteria, Chlorophyceae, Bacillariophyceae and Euglenophyceae mostly represented the phytoplankton. Bacillariophyceae dominated the phytoplanktonic portion of stomach contents at small fish size (<75 g/fish), while Chlorophyceae is the dominant group at large fish size (> 75 g/fish). Fish could select Cyanobacteria and Euglenophyceae at all fish weights, meanwhile Chlorophyceae and Bacillariophyceae were eaten with slight selectivity at larger weights..

Stepwise temperature regulation and its effect on growth, feeding and muscle growth patterns of juvenile Atlantic halibut (Hippoglossus hippoglossus L.)

To investigate the possible direct effect of a stepwise reduction in temperature with increasing size on growth, feeding parameters and muscle growth patterns of juvenile Atlantic halibut (Hippoglossus hippoglossus L.), 804 juvenile halibut (mean initial weight individuals: 14.2 g ± 0.2 SEM) were reared at constant 9, 12 and 15°C or shifted (T-step, i.e. 15–12°C after 36 days) for 99 days. Despite indications of lower optimal temperature for growth with increasing size, equal end weights were obtained between the constant 12°C, constant 15°C and T-step groups. Best overall growth was observed for the group kept at constant 12°C. The limited effect of the T-step group may relate to the size at movement (too big), the temperatures investigated (close to optimum) and the time and size interval investigated (too narrow). Differences in growth were reflected more by alterations in feed intake (C T and F%) than by differences in feed conversion efficiencies (FCE). Differences were found with respect to the density of muscle cells, whereas no differences were found between the average muscle cell diameters. The mean diameter of muscle cells tended to increase only slightly with increasing fish weight, while the mean density of muscle cells tended to decrease. Using an optimum temperature of 12°C, an indication of a possible increased rate of hyperplasia in relation to higher growth was seen.

Estimation of digestible protein and energy requirements of yellowtail kingfish Seriola lalandi using a factorial approach

This study used a factorial approach to estimate the digestible protein (DP) and energy (DE) requirements of yellowtail kingfish Seriola lalandi weighing between 50 to 2000 g and reared at 20–25 °C. The factorial model was subsequently used to calculate theoretical changes in the optimum ratio of DP:DE (g DP MJ DE −1) and estimate changes in the theoretical feed conversion ratio (FCR) or feed intake with increasing fish size. Growth of S. lalandi was described by the function; growth (g fish −1 d −1) = 0.268 ± 0.33 BW (g) 0.52 ± 0.2 . Body weight exponents for protein or energy loss in S. lalandi were found to be statistically similar to 0.7 or 0.8, respectively. Maintenance requirements for DP were found to be 1.70 g DP BW (kg) −0.7 d −1 while those for DE were found to be 87.44 kJ BW (kg) −0.8 d −1. Utilisation coefficients for DP or DE estimated from linear regressions which incorporated data above and below maintenance ration were 0.51 and 0.65, respectively. However, regressions which excluded data below maintenance ration returned coefficients of 0.41 (DP) and 0.55 (DE). The partial energetic efficiencies of protein ( K P ) and lipid ( K L ) deposition as estimated by multiple linear regression were 0.61 and 0.83, respectively. Piecewise linear regression analysis was applied to the curvilinear response of DP:DE on increasing fish weight in order to differentiate key growth stages in the production of S. lalandi. Three stages were identified; a juvenile stage ≤ 200 g, an intermediate stage between 200 and 1000 g and a stage for fish ≥ 1000 g. These stages corresponded to DP:DE requirements of 38, 31 and 24 g DP MJ DE −1, respectively. Practical diet formulations that would best meet the DP:DE criteria for fish ≤ 200 g are those which contain approximately 456 g DP kg −1 and 12 MJ DE kg −1. For fish growing between 200 and 1000 g a diet containing 465 g DP kg −1 and 15 MJ DE kg −1 would be suitable while a diet containing 432 g DP kg −1 and 18 MJ DE kg −1 would be appropriate for fish ≥ 1000 g. Further evaluation of growth potential and nutrient requirements at different water temperatures will assist in improving the utility of this model.

Studies on the endoparasites in the gastro-intestinal tract of &lt;i&gt;Clarias garienpinus&lt;/i&gt; (Tugels) in Wase Dam, Kano State, Nigeria.

A survey of helminth parasites of the alimentary canal of C. garienpinus was carried out in Kano, between January, 2002 and June 2002. A total of 700 fish samples were examined out of which 281 (40.14%) were infected. The parasites recovered include: Cestodes (Polyonchobothrium sp. and Monobothroids sp.), nematodes (Procamallanus sp. and Paracamallanus sp) and metacercarial cysts of trematodes. Of all the parasites recovered nematodes have the highest occurrence of (40.82%). There was higher infection with increasing fish weight. There was also a high correlation between weight and length of fish (P

Potential of local agricultural by-products for the rearing of African catfish Clarias gariepinus in Rwanda: effects on growth, feed utilization and body composition

This study was performed to evaluate the effect of replacing fish meal with local by-products on Clarias gariepinus growth performance, feed utilization and body composition. A control diet contained 50% of fish meal. In four other diets, fish meal was partially replaced by vegetable and animal protein blend composed of sunflower oil cake, soybean oil cake, groundnut oil cake, bean meal, chicken viscera and blood meal. The study was conducted in a recirculating water system at a mean temperature of 23.6°C. The five test diets were compared with a commercial diet developed for African catfish. All diets were balanced to be equal in gross energy (19 kJ g−1) and crude protein (40%). The experimental groups were fed in triplicate for 8 weeks, increasing fish weight from about 6.2 g at start to 52.3 g in the end. Best specific growth rate (SGR=3.4), feed efficiency (FE=1.3) and protein efficiency ratio (PER=3) were obtained with the control diet (diet 50% fish meal), although there were no significant differences between the group of fish fed the control diet and those fed diets based on groundnut oil cake or bean meal, whereas SGR (2.17), FE (0.85) and PER (1.95) were significantly (P<0.01) lower in fish fed diet containing sunflower oil cake. No significant differences (P<0.05) were found in fish fed commercial diet and diets containing bean meal or groundnut oil cake. Groundnut oil cake or bean meal can thus replace at least 50% of fish meal in the diet of Clarias fingerlings without amino acid supplementation. Because of its economic importance and its potential in animal nutrition sunflower oil cake is still an interesting feed ingredient, but its efficiency should be improved by various processing techniques. African catfish can utilize efficiently a diet with low percentage of animal protein without growth reduction.

Growth, feed efficiency, digestibility and nutrient distribution in Atlantic cod (Gadus morhua) fed two different fish meal qualities at three dietary levels of vegetable protein sources

Atlantic cod were fed six diets where the ratio of protein from fish meal to vegetable protein were varied from 91%, 67% to 46%, respectively. The experimental groups were performed in triplicate in a 20 week growth trial, increasing fish weight from about 167 g to 690 g. The vegetable protein sources constituted full-fat soybean meal and corn gluten meal at a fixed ratio of 1:2, and replaced either a high quality fish meal (DC Mink 92.3%) or a lower quality fish meal (DC Mink 85.6%) in the diet. All diets were extruded and balanced to be equal in gross energy, crude protein, lipid, carbohydrate, lysine and phosphorus. No difference in growth (SGR 1%) was observed comparing the two fish meal qualities. However, feed intake was significantly higher (9%) and feed efficiency lower (10%) for lower quality fish meal compared to high quality fish meal. Protein and amino acid digestibility was significantly reduced in the lower quality fish meal, while unaffected by vegetable protein inclusion for both fish meal qualities. Protein utilization as measured by protein efficiency ratio and net protein value was not affected by fish meal inclusion, except in the diet using lower quality fish meal and high vegetable protein inclusion. Lipid and energy digestibility was significantly reduced by vegetable protein inclusion for both fish meals. The lower fish meal quality increased lipid deposition in the liver and affected slaughter quality of cod by increasing HSI and dressing out percentage at low and intermediate substitution levels. Muscle composition showed small dietary changes except for arginine, while liver fatty acid composition clearly reflected fatty acid profile of full-fat soya in the diets. Corn gluten meal and full-fat soybean meal (2:1) can replace approximately 50% of dietary protein without affecting feed intake, growth, protein digestibility or slaughter quality of cod when exchanging high quality fish meal. For the lower quality fish meal diets some lower inclusion of vegetable protein sources seem to be acceptable.

Seasonal variations in muscle growth dynamics and selected quality attributes in Atlantic halibut ( Hippoglossus hippoglossus L.) fed dietary lipids containing soybean and/or herring oil under different rearing regimes

Atlantic halibut ( Hippoglossus hippoglossus), 1630 ± 510 g at the start of the experiment were reared in tanks for 1 year and subjected to three different environmental regimes; Continuous light and Constant temperature (CC), Natural light and Constant temperature (NC) or Natural light and Ambient temperature (NA). Two diets were fed, where 50% of the dietary lipids were either herring oil or soybean oil supplemented. The fish were sampled in May, August and November the first year, and February and May the following year. The CC groups grew better than the NC and NA groups from May to November, and as a result had a significantly ( p < 0.05) higher weight by the end of the experiment. This difference did however not affect muscle fibre size distribution, or the chosen muscle quality attributes texture, fat content, water or fat loss of the fillet. These quality attributes were influenced by season and body weight, whereas diet had no significant effect. The NA group had lower fat content of the fillet than the other environmental regimes in August, November and May end, and fat content increased with increasing fish weight. Water and fat losses were lowest in November and February. The diet influenced the fatty acid profile of the musculature; the triacylglycerol fraction reflecting the dietary treatment while the polar fraction was less influenced by diet. The hardness of the fillet was not influenced by the environmental regimes, but by season, and hardness was at its lowest in August, and increased towards the following spring. The muscle fibre distribution varied only with season, and neither treatment nor diet had any effect on the muscle growth dynamics. Recruitment of new fibres seemed mainly to occur during winter, signified by maximum occurrence of fibres < 500 μm 2 by the end of the experiment in May.

Feeding and control of blue-green algal blooms by tilapia (Oreochromis Niloticus)

Outbreak of blue-green algal blooms, with associated unsightly scum and unpleasant odor, occurs frequently in eutrophic lakes. We conducted feeding experiments to study ingestion and digestion of Microcystis aeruginosa by tilapia (Oreochromis niloticus) under laboratory conditions and field testing to reduce Microcystis blooms by stocking tilapia in Lake Yuehu and other eutrophic waters in Ningbo, China between 2000 and 2003. Our results show that tilapia was capable of ingesting and digesting a large quantity of Microcystis. Digestion efficiency ranged from 58.6 to 78.1% at water temperature of 25 °C. Ingestion rate increased with increasing fish weight and water temperature. Intensive blooms occurred in Lake Yuehu in both 1999 and 2000. The lake was stocked with silver carp (Hypophthalmichthys molitrix), bighead (Aristichthys nobilis) and a freshwater mussel (Hyriopsis cumingii) at a total biomass of 9.8 g m−3 in early 2001, and tilapia at 3–5 g m−3 in April of 2002. From June to October, average phytoplankton density decreased from 897.6×106 cells l−1 in 2000 to 291.7×106 cells l−1 in 2001 and 183.0×106 cells l−1 in 2002. Compared to 2000, the annual average phytoplankton biomass in 2001 and 2002 decreased by 48.6% and 63.8%, respectively. The blue-green algal biomass which made up 70% of the total phytoplankton biomass in 2000 was reduced to 22.1% in 2001 and 11.2% in 2002. Meanwhile, Secchi depth increased from 20–50 cm to 55–137 cm during the same time period. Similar results were observed in some other eutrophic waters. For example, algal bloom disappeared about 20 days after tilapia fingerlings were stocked (8–15 g m−3) to a pond in Zhenhai Park. Chlorophyll a concentration and phytoplankton production declined dramatically whereas water transparency increased substantially. However, the impacts of tilapia on nitrogen and phosphorus dynamics in natural lakes need further investigation. Our studies revealed that stocking tilapia is an effective way to control algal blooms in eutrophic waters, especially in lakes where nutrient loading cannot be reduced sufficiently, and where grazing by zooplankton cannot control phytoplankton production effectively.

Energy Density of Lake Whitefish Coregonus clupeaformis in Lakes Huron and Michigan

We collected lake whitefish Coregonus clupeaformis off Alpena and Tawas City, Michigan, USA in Lake Huron and off Muskegon, Michigan USA in Lake Michigan during 2002–2004. We determined energy density and percent dry weight for lake whitefish from both lakes and lipid content for Lake Michigan fish. Energy density increased with increasing fish weight up to 800 g, and then remained relatively constant with further increases in fish weight. Energy density, adjusted for weight, was lower in Lake Huron than in Lake Michigan for both small (≤800 g) and large fish (>800 g). Energy density did not differ seasonally for small or large lake whitefish or between adult male and female fish. Energy density was strongly correlated with percent dry weight and percent lipid content. Based on data from commercially caught lake whitefish, body condition was lower in Lake Huron than Lake Michigan during 1981–2003, indicating that the dissimilarity in body condition between the lakes could be long standing. Energy density and lipid content in 2002–2004 in Lake Michigan were lower than data for comparable sized fish collected in 1969–1971. Differences in energy density between lakes were attributed to variation in diet and prey energy content as well as factors that affect feeding rates such as lake whitefish density and prey abundance.

Development of a Bioenergetics Model for the Round Goby ( Neogobius melanostomus)

The round goby ( Neogobius melanostomus) was introduced into the Great Lakes in the 1990s through ballast water transfer. Gobies are potential vectors for material transfer between the benthic and pelagic zones. A bioenergetics model was developed for round gobies to enable us to quantify the flow of energy, contaminants, and nutrients from the benthos to pelagic fishes. Weight- and temperature-dependent coefficients for metabolism and consumption were derived. Food consumption increased with temperature up to 26°C before sharply decreasing, and weight-specific consumption decreased with increasing fish weight (allometric coefficient = −0.256, SE = 0.160). Specific oxygen consumption was inversely related to body mass (allometric coefficient = −0.157, SE = 0.025) and increased exponentially with temperature. Estimated Q 10 for respiration was 1.84. Additional parameters were obtained from the literature to describe specific dynamic action, egestion, excretion, and reproductive losses. The bioenergetics model explained growth of round gobies in Lake Erie and in their native range.

Influence of tropical seasonal changes on oocyte diameter, responses to hormonal induction and hatching quality in two strains of the catfish, Heterobranchus longifilis Val. (Clariidae)

A comparison was made between the oocyte diameter, pseudo-absolute fecundity (PAF) and egg quality of two strains of the catfish, Heterobranchus longifilis, maintained in outdoor ponds under a tropical highland climate in Cameroon. The results indicated that circannual endogenous rhythms for ovarian recrudescence and regression are absent in H. longifilis, irrespective of breeding history, age and strain. There appeared to be a possible slight adverse effect of climate (dry season) on reproductive performance of both strains. Oocyte diameter and PAF increased with increasing fish weight when data from both strains were combined, indicating that the two strains may exhibit the same reproductive performance. Viable eggs were obtained all year round after hormonal induction. It is concluded that for propagation of H. longifilis in tropical African countries, broodfish could be maintained in outdoor earthen fish ponds with proper feeding.