Growth of 0+ perch (Perca fluviatilis) predating on 0+ bream (Abramis brama)

Abstract – Larvae and juveniles of perch Perca fluviatilis and bream Abramis brama of Lake Speldrop, a highly eutrophicated gravel-pit lake in the floodplain of the Lower Rhine, were used in laboratory experiments to study predation of perch on bream. In the first series of experiments (control), 0+ perch of 30 mm total length (TL) did not prey on 0+ roach of about 24 mm TL. The perch fed only on zooplankton, resulting in low growth rates of 0.17 mm  ·  day⁻¹. In the second series of experiments, perch (30 mm TL) were combined with 0+ bream with an average TL of 14 and 19 mm at different ratios. As in the first series, even a nine-fold higher amount of zooplankton food had no significant influence on the growth rate of perch, regardless of the perch:bream ratio. At a perch: bream ratio of 7:1 and 4:4 all bream were eaten by the perch and restocked twice daily. At the end of the experiment, the TL of perch at a perch:bream ratio of 7:1 was significantly lower compared to a perch:bream ratio of 4:4 (mean growth rates at 7:1 of 0.16 mm  ·  day⁻¹ and at 4:4 of 0.35 mm  ·  day⁻¹). At the perch:bream ratio of 1:7, perch fed on bream in varying amounts, averaging between 3 and 12 bream per day and per individual. After 20 days, the final length of these fish was always significantly higher than the TL of perch at other perch:bream ratios and increased in correlation to number of bream eaten per day (mean growth rate 1.13 mm  ·  day⁻¹). The results are discussed with respect to the piscivore-dominated fish community of the eutrophied Lake Speldrop. ^Note     

Growth of juvenile tilapia, Oreochromis niloticus L. from Lakes Zwai, Langeno and Chamo (Ethiopian rift valley) based on otolith microincrement analysis

Abstract – Age and growth of juvenile tilapia, Oreochromis niloticus , from Lakes Zwai, Langeno and Chamo (Ethiopia) were studied from microincrements in otoliths. Growth in length was best described by the Gompertz model. Average growth rate of the fish was most rapid in Lake Chamo (0.39 mm  ·  day⁻¹, 1.14%  ·  day⁻¹), intermediate in Lake Zwai (0.20 mm  ·  day⁻¹, 0.72%  ·  day⁻¹) and slowest in Lake Langeno (0.16 mm  ·  day⁻¹, 0.62%  ·  day⁻¹). Similarly, back-calculation from otolith increment widths gave growth rates of 0.28 to 0.43 mm  ·  day⁻¹, 0.15 to 0.32 mm  ·  day⁻¹ and 0.11 to 0.28 mm  ·  day⁻¹ for Chamo, Zwai and Langeno fish, respectively. In addition, Fulton's condition factor was largest for Chamo tilapia and smallest for Langeno tilapia; the difference between fish from Langeno and Zwai was small. Rapid growth of juvenile O. niloticus in Lake Chamo was attributed to warm temperature and better food quality. ^Note     

Effects of different feeding level on the growth, feed efficiency and body composition of juvenile mangrove red snapper, Lutjanus argentimaculatus (Forsskal 1775)

The effects of several feeding levels (1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4% and 4.5% of body weight per day, BW day⁻¹) on the growth, feed efficiency and body composition of juvenile Lutjanus argentimaculatus (body weight 27.1 g) were examined. Fish were fed a test diet (40% protein, 18.4% lipid and 13.4 kJ g⁻¹) for 75 days in three equal meals. Weight gain and specific growth rate increased with increasing feeding level up to 2.5% BW day⁻¹, after which no significant improvement in growth was observed. The feed efficiency, protein efficiency ratio, retention of protein and digestibility of nutrients did not differ for fish fed 1–2.5% BW day⁻¹, but decreased significantly when feeding levels were increased above 3% BW day⁻¹. The chemical compositions of whole fish or body organs were significantly affected by the feeding level. The condition factor, mesenteric fat, hepato- and viscerosomatic indices were higher in fish fed 2.5–4.5% BW day⁻¹. The cholesterol, triglycerides and haematocrit values were similar among treatments, except that high levels of plasma lipids were recorded in fish fed at 2.5% BW day⁻¹. Taking into consideration the growth, feed efficiency and body composition data attained in this study, a feeding level of 2.5% BW day⁻¹ is recommended for juvenile L. argentimaculatus weighing between 27 and 140 g.     

Comparative performance of juvenile red abalone, Haliotis rufescens, reared in laboratory with fresh kelp and balanced diets

Juvenile Haliotis rufescens were reared in the laboratory in order to investigate the extent to which fresh kelp and formulated feeds with 250 g kg⁻¹ (25P) and 380 g kg⁻¹ protein content (38P) affected their growth rate, gut residence time (GRT), food consumption ( C ), food conversion ratio (FCR) and digestibility. Abalone from 38P attained the highest growth rate (70.5 ± 4.2 μm day⁻¹; 98.3 ± 6.95 μg day⁻¹), followed by 25P (47.9 ± 2.79 μm day⁻¹; 67.4 ± 2.82 μg day⁻¹) and kelp (23.6 ± 3.36 μm day⁻¹; 28.2 ± 4.11 μg day⁻¹). No significant differences were observed in consumption rate among treatments (0.61–0.68% body weight per day), yet kelp-fed abalone exhibited higher FCR (2.44), protein efficiency ratio (4.42), and apparent digestibility of dry matter (69.5%), protein (69.8%) and gross energy (79.2%) than 38P organisms (59.8, 62.4 and 62.2%, respectively). They also showed longer GRT (23.1 ± 0.93 h). This study demonstrated that formulated diets with 250 g kg⁻¹ and 380 g kg⁻¹ protein inclusion can sustain higher growth rates of juvenile H. rufescens than fresh algae. These differences seem to be due to the amount of dietary protein. Kelp meal appears to improve the consumption and digestibility of balanced diets, and its inclusion in formulated diets is recommended.     

Survival and movement of hatchery-reared red snapper on artificial habitats in the northern Gulf of Mexico

Abstract  Hatchery-reared age-0 red snapper, Lutjanus campechanus (Poey), were released onto artificial habitats in the Gulf of Mexico. Fish showed 12.7% survival after 7 months on small habitats (0.86 m³) and 3.1% survival after 8 months on large habitats (3.9 m³). Emigration was estimated by the movement of fish to unstocked habitats and accounted for 76.8% of the total decline in abundance at release sites after 26 days. Fish showed higher survival and growth rates on small habitats (27.6% at 26 days; 0.33 mm day⁻¹) compared with large habitats (13.2% at 34 days; 0.26 mm day⁻¹), which may have been due to increased predation and competition on large habitats. Fish became evenly distributed among adjacent habitats 26 days after release, indicating that stocking densities at release habitats were above carrying capacities. These observations suggested that providing additional habitat around red snapper release sites would increase survival.     

Effects of dietary protein to metabolizable energy ratios and total protein concentrations on the performance of yellow perch Perca flavescens

Juvenile yellow perch Perca flavescens were fed semipurified diets with varying protein to metabolizable energy ratios (PME, g protein MJ⁻¹ metabolizable energy) and nutrient densities in three experiments to determine recommended dietary protein and energy concentrations. Experiment 1 fish (18.6 g) were fed diets containing 450 g crude protein kg⁻¹ dry diet and 14.5–18.8 MJ ME kg⁻¹ dry diet for 10 weeks. No differences were found in the growth of experiment 1 fish fed the different diets. Experiment 2 fish (21.9 g) were fed diets containing 15.7 MJ ME kg⁻¹ dry diet and 210–420 g crude protein kg⁻¹ dry diet for 8 weeks. Fish fed the diet containing 340 g kg⁻¹ protein (diet PME = 22) exhibited the greatest weight gain. Experiment 3 fish (27.1 g) were fed diets with a PME of 22 and varying nutrient density (yielding 205–380 g crude protein kg⁻¹ dry diet) for 8 weeks. No differences were found in the growth of experiment 3 fish. Yellow perch fed the semipurified diets exhibited increased liver fat content, liver size and degree of liver discoloration compared with fish fed a commercial fish meal-based diet. Liver changes may have resulted from high dietary carbohydrate levels. We conclude that a protein level of 210–270 g kg⁻¹ dry diet is suitable for juvenile yellow perch provided that the dietary amino acid profile and carbohydrate content are appropriate for yellow perch.     

Alternative use of food resources causes intra-cohort variation in the size distribution of young-of-the-year perch (Perca fluviatilis)

Abstract –  Body sizes of young-of-the-year (YOY) perch ( Perca fluviatilis ) at the end of their first summer are extremely variable and range in different studies between 4 and 15 cm. To analyse whether size divergences in YOY perch may be attributed to alternative use of food resources, adult perch were stocked into two previously fishless ponds and growth, size distribution and food intake of the YOY perch were recorded. In addition to perch, adult bream ( Abramis brama ) were introduced to produce juvenile bream that could serve as a food resource for YOY perch. The body sizes of YOY perch at the end of the experiment ranged from 32 to 168 mm with a bimodal size distribution. The combination of stomach content analyses and stable isotope signatures revealed that the small size cohort were planctivorous/benthivorous while the large size cohort was piscivorous/cannibalistic. Results implicated that different feeding behaviour contributed to the size divergences in YOY perch and that the extreme growth of the large size cohort was induced by piscivory.     

Patterns of growth of juvenile pink abalone Haliotis corrugata fed re-hydrated natural feeds at a laboratory and a hatchery

The feasibility of obtaining a similar growth response from juvenile pink abalone Haliotis corrugata at a research laboratory and a hatchery, when using natural feeds was evaluated. Four macroalgae, Egregia menziesii , Eisenia arborea , Macrocystis pyrifera , Gracilaria sp., and the surfgrass Phyllospadix torreyi were used as feeds. Response patterns of abalone were very similar at both facilities in terms of final length, weight, and survival, varying from 13.0 to 15.50 mm, 0.31 to 0.52 g, and 60.0% to 78.6%, respectively. Better growth was obtained when E. menziesii , M. pyrifera , and Gracilaria sp. were offered. Poor results were obtained with surfgrass. The feed conversion ratio was determined at the laboratory and did not vary significantly, ranging from 42.3 to 199.0; although a significant inverse correlation was observed with growth rate. Growth in length and weight and survival rates varied within 1.6–20.2 μm day⁻¹, 0.123–1.664 mgday⁻¹, 0.4–0.64%day⁻¹, respectively. Mean growth rate in length (14.7μm day⁻¹) and weight (1.18 mg day⁻¹) at the hatchery were significantly higher than that obtained at the laboratory (9.4 μm day⁻¹ and 0.77 mg day⁻¹), which is most likely a consequence of more suitable water temperature at the hatchery. Mean survival rate was significantly higher at the laboratory (53.1%day⁻¹) than at the hatchery (46.1%day⁻¹).     

The effects of mechanically reducing northern pike density on the sport fish community of West Long Lake, Nebraska, USA

Abstract  Removal of piscivores may affect population size structure, abundance and growth rates of the remaining fish community. A total of 572 northern pike, Esox lucius L., was removed from 25-ha West Long Lake, Nebraska from 2003 to 2006. The northern pike population was reduced from 36 fish ha⁻¹ and 22 kg ha⁻¹ in 2002 to 20 fish ha⁻¹ and 9 kg ha⁻¹ in 2006. The northern pike population shifted to dominance by smaller individuals. Relative abundance increased for bluegill, Lepomis macrochirus Rafinesque, but remained similar between years for largemouth bass, Micropterus salmoides (Lacepède), and yellow perch, Perca flavescens (Mitchill). Bluegill and yellow perch size structure increased probably because of reduced predation by northern pike. The effects of reduced northern pike density on largemouth bass were less evident. The largemouth bass population may be returning to higher density with smaller size structure observed before pike were introduced. The sport fish community responded positively to the removal of northern pike in this small lake.     

Energy and protein requirements for maintenance and growth in gilthead seabream (Sparus aurata L.)

Factorial determinations of energy and protein requirements in growing Sparus aurata were carried out at 23–24°C. The energy content in the whole fish was dependent on fish weight and ranged from 5 to 11 MJ kg⁻¹ body mass for 1–250 g fish, whereas the protein content remained constant at 179 g kg⁻¹.
During starvation the fish lost 42.5 kJ body weight (BW) (kg)^−0.83 day⁻¹ and 0.42 g protein BW (kg)^−0.70 day⁻¹. The maintenance requirement for energy was calculated to be 55.8 kJ BW (kg)^−0.83 day⁻¹ and for protein 0.86 g BW (kg)^−0.70 day⁻¹. Utilization of digestible energy and digestible crude protein below and at maintenance was determined as 0.72 and 0.51, respectively. Utilization of digestible energy and digestible crude protein for growth above maintenance was determined as 0.46 and 0.28, respectively.
These values allow estimation of requirements for growing Sparus aurata .     

Nutrient values of dietary ascorbic acid (l-ascorbyl-2-polyphosphate) on growth, survival and stress tolerance of larval shrimp, Litopenaeus vannamei

l -ascorbyl-2-polyphosphate (ApP) was used as a vitamin C source to investigate the ascorbic acid (AsA) requirements on growth performance and stress resistance of the larval white shrimp, Litopenaeus vannamei . Five isoenergetic and isonitrogenous fish meal-fish protein hydrolysate-based diets with five levels of ApP, AsA equivalent to 91.8, 188, 271, 360 and 436 mg kg⁻¹ diet were fed to triplicate groups of L. vannamei (mean initial wet weight 1 mg) for 32 days. The diet with AsA 91.8 mg kg⁻¹ showed high cumulative mortality after 10 days of feeding. After the 32-day trial, the shrimp that fed the diet had significantly lower survival and weight gain (WG, %) than those that fed 188, 271, 360 and 436 mg AsA kg⁻¹ diets. Specific growth rate (SGR, % day⁻¹) and final body wet weight (FBW, mg) showed the same pattern as WG (%). There were no significant differences in growth performance (FBW, WG and SGR) among the groups that fed 188, 271, 360 and 436 mg kg⁻¹ of AsA at the termination of feeding trial. Broken-line regression analysis on WG indicated that 191 mg AsA kg⁻¹ in the diet was the optimum for larval L. vannamei . On the contrary, dietary level of more than 360 mg AsA kg⁻¹ was needed to ensure high resistance to stressful conditions such as low dissolved oxygen stressors.     

Effect of feeding regime and temperature on ongrowing results of pikeperch (Sander lucioperca L.)

This study aimed to determine the effect of feeding rates and water temperatures on the growth, feed utilization and size heterogeneity changes in subadult pikeperch. Fish with an average weight of 84±19 g were fed with a commercial trout diet for 18 weeks at a water temperature of 20 °C and 25 °C. Four feeding rates (PSFR) were predicted at both temperatures, which corresponded to 1.0%, 1.25%, 1.50% and 2.0% of body weight per day (bw day⁻¹) for the first, and to 0.8%, 1.0%, 1.2% and 1.4% of bw day⁻¹ for the second 9 weeks respectively. At the end of the experiment, the individual weight averaged 273±82 g. Pikeperch showed a better growth rate [specific growth rate (SGR)] and apparent feed conversion rates (AFCR) at the higher temperature. Thermal-unit growth coefficient (TGC) was better at the lower temperature. The values of SGR, TGC and AFCR significantly increased with increasing PSFR at both temperatures. The values of TGC plotted against the computed feeding rates allowed estimation of the maximum feeding rates (1.25% and 1.15% of bw day⁻¹ for pikeperch of 150–180 g at 25 and 20 °C respectively). Size heterogeneity changes were affected neither by the feeding rate nor by temperature.     

Does timing of daily feeding affect growth rates of juvenile three‐spined sticklebacks,Gasterosteus aculeatus L?

Abstract – To assess the consequences of unpredictability in the availability of food, this study measured the effect of timing of the daily feeding on food consumption and growth rates of juvenile Gasterosteus aculeatus. The experiment lasted 21 days at 14 °C and a photoperiod of 10 hours of light and 14 hours of dark. Fish were housed individually and allocated at random to three treatments. The mean initial weight of fish was 0.402 g. Group 1 were fed live enchytraeid worms for 2 h after lights came on ("morning"), group 2 was offered food for 2 h randomly at any time of the day ("random") during the light period and group 3 received food for 2 h before the lights went off ("evening"). There was no significant effect of timing of feeding on mean daily food consumption, which was 0.052 g day⁻¹. Daily consumption on the random schedule was more irregular than on the two fixed schedules. Timing of feeding had no significant effect on mean specific growth rate (G) (2.42% day⁻¹), gross growth efficiency (23.3%), white muscle RNA:DNA ratio (5.6), carcase lipid content (31.7% dry wt) and carcase dry matter content (27.4% wet wt). Thus, a lack of predictability in the availability of food during the light period of the day did not impose a detectable cost on the growth performance of the stickleback.     

Dynamic in-lake spawning migrations by female sockeye salmon

Abstract –  Precise homing by salmon to natal habitats is considered the primary mechanism in the evolution of population-specific traits, yet few studies have focused on this final phase of their spawning migration. We radio tagged 157 female sockeye salmon ( Oncorhynchus nerka ) as they entered Lake Clark, Alaska, and tracked them every 1–10 days to their spawning locations. Contrary to past research, no specific shoreline migration pattern was observed (e.g., clockwise) nor did fish enter a tributary unless they spawned in that tributary. Tributary spawning fish migrated faster (mean = 4.7 km·day⁻¹, SD = 2.7, vs. 1.6 km·day⁻¹, SD = 2.1) and more directly (mean linearity = 0.8, SD = 0.2, vs. 0.4, SD = 0.2) than Lake Clark beach spawning fish. Although radio-tagged salmon migrated to within 5 km of their final spawning location in an average of 21.2 days (SD = 13.2), some fish migrated five times the distance necessary and over 50 days to reach their spawning destination. These results demonstrate the dynamic nature of this final phase of migration and support studies indicating a higher degree of homing precision by tributary spawning fish.     

Use of salt to control ichthyophthiriosis and prevent saprolegniosis in silver perch, Bidyanus bidyanus

The ciliate protozoan, Ichthyophthirius multifiliis , and the fungus, Saprolegnia parasitica , cause the diseases ichthyophthiriosis and saprolegniosis respectively. Both diseases are difficult to control and can cause high mortalities of freshwater fish, including the Australian silver perch, Bidyanus bidyanus (Mitchell). The efficacy of salt (NaCl) in controlling and preventing these diseases in silver perch was evaluated in aquaria and tanks. Low pH levels were also evaluated as a control for ichthyophthiriosis. Concentrations of 2 or 3 g L⁻¹ salt controlled infestations of I. multifiliis , and fish were free of both theronts and trophonts by day 8 at temperatures of 17.3–21.3 °C and by day 6 at 19.2–23.5 °C. Fish treated with 1 g L⁻¹ salt remained infested and all fish in a control treatment (0 g L⁻¹ salt) died. Although the mean survival rates of infested fish at pH levels of 5 or 6 were only 13.9% and 7.6%, respectively, there were no theronts or trophonts on surviving fish after 12 days. Silver perch harvested from a pond and treated with 2 or 3 g L⁻¹ salt did not become infected with S. parasitica and survival was 100%, whereas 16.6% of untreated (0 g L⁻¹ salt) fish became infected and survival was only 66.7%. A concentration of 2 g L⁻¹ NaCl is recommended for the control of ichthyophthiriosis and the prevention of saprolegniosis in silver perch held in tanks, aquaria and re-circulating aquaculture systems.     

Effect of antibiotic treatment on the growth and survival of juvenile northern Chilean scallop, Argopecten purpuratus Lamarck (1819), and associated microflora in experimental cultures

Juvenile northern Chilean scallops of 937±55 μm shell height were exposed to five different concentrations of chloramphenicol (CHL) (5, 10, 25, 50 and 100 μg mL⁻¹), plus a control without antibiotics. To determine the effect of CHL on the accompanying microflora, the number of colony-forming units (CFU) that grew on TGE culture medium was counted in the seawater of containers with juveniles, and in containers with microalgae used as food. Both were exposed to the same concentrations of CHL. The growth rates of juveniles treated with CHL and the control without antibiotic showed highly significant differences ( P =0.0001). The growth rate was inversely proportional to the CHL concentration. The control sample presented the highest growth rate (84.4±14.3 μm day⁻¹), followed by the sample treated with 5 μg mL⁻¹ (64.2±14.3 μm day⁻¹). The survival in the control and in the treated samples with 5–50 μg mL⁻¹ was rather high, with a mean value of 95%. Only the sample treated with 100 μg mL⁻¹ had a low survival (36.7%). The CFU count was larger in the containers with juveniles, when compared with the ones with food. The CFU count tended to decrease with increasing CHL concentration in the juveniles.     

Juvenile growth of two tilapia species in lakes Naivasha and Baringo, Kenya

Abstract –  Tilapia species in East African lakes often form the basis of commercial fisheries, with information on their population biology assisting their management. This study utilised otolith microstructure, with validation by modal progression analysis, to provide growth data for two tilapia species in two Kenyan lakes for the first time. Otolith microstructure revealed the growth rate of Oreochromis niloticus baringoensis , a sub-species endemic to Lake Baringo, was fast compared with populations of Oreochromis niloticus ; mean daily growth rates were >0.50 mm·d⁻¹ in fish between 12 and 53 mm total length. Growth of Oreochromis leucostictus in Lake Naivasha was also relatively fast when compared with the growth rates of other tilapia species, with mean daily growth rates of approximately 0.35–0.48 mm·d⁻¹ in fish between 10 and 56 mm total length. Growth rates of both species were well described by the Gompertz model and were corroborated by modal progression analysis that revealed similar daily growth rates in modes of young-of-the-year fish.     

Fishery resources and economic gain in three mangrove areas on the south-east coast of India

Abstract The fishery resources and fishing income in three different mangrove areas were evaluated. The mangrove-rich area provided high catches of shellfish and finfish and yielded high fishery income, compared with the mangrove-poor areas. Luxuriant mangrove areas supported a catch of 11 kg shellfish ha⁻¹ day⁻¹ and 4.5 kg finfish ha⁻¹ day⁻¹, corresponding with an economic gain of US$ 14 (Rs 603.7) day⁻¹ for shellfish and US$ 3 (Rs 130.5) day⁻¹ for finfish. The value of maintaining mangroves to ensure better fishery resources and to support coastal economies was identified. Management practices for conserving and enhancing mangroves and associated fishery resources are suggested.     

The efficacy of emamectin benzoate as an oral treatment of sea lice, Lepeophtheirus salmonis (KrÒyer), infestations in Atlantic salmon, Salmo salar L.

The efficacy of emamectin benzoate as an oral treatment of sea lice, Lepeophtheirus salmonis (KrÒyer), infestations in Atlantic salmon, Salmo salar L., was evaluated in a dose titration study and two dose confirmation studies. Replicated groups of salmon with induced infestations of sea lice were given emamectin benzoate on pelleted feed at doses of 0, 25, 50 and 100 μg kg⁻¹ biomass day⁻¹ for seven consecutive days. Sea lice were counted at 7, 14 and 21 days from the start of treatment, and comparisons made with control fish given the same diet without emamectin benzoate. Total numbers of sea lice were significantly reduced at all doses in all three studies when compared to control fish. There was no significant difference between doses of 50 and 100 μg kg⁻¹, but the 50 μg kg⁻¹ dose resulted in significantly fewer lice than the 25 μg kg⁻¹ dose. Emamectin benzoate was highly effective in reducing numbers of preadult and adult lice and prevented the maturation of chalimus to motile stages. The optimum therapeutic dose was selected as 50 μg kg⁻¹ day⁻¹ for seven days. Treatment reduced the incidence of epidermal damage by sea lice and, in one study, survival of treated fish was 48% higher than in control groups. No fish mortalities or adverse effects were attributed to treatment with emamectin benzoate at any of the doses tested.     

Individual and population-level food consumption by cyprinids and percids in a mesotrophic lake

Abstract – Mesotrophic Lake Pohjalampi in eastern Finland was fished intensively from 1992 to 1996. In 1996, the biomasses of the dominant fish species, roach and bream, were reduced to 14% and 6%, respectively, of that in 1992. The total biomass of percids was, however, unchanged or slightly increased. The proportion of benthic invertebrates in the total food of the fish decreased from 57% to 36% during the study period, whereas the proportion of zooplankton increased from 31% to 56%. At the same time the number of young planktivorous fish increased. Thus, the main object of fish predation turned from benthic invertebrates to zooplankton due to change in fish population structure. At the beginning of the study the amount of detritus eaten by cyprinids was about 620 kg  ·  ha⁻¹  ·  year⁻¹, but this decreased by 82% due to the intensive fishing. Thus, by recycling nutrients from the sediment, the detrivorous-benthivorous feeding of cyprinids is an important factor in the nutrient balance of the lake. ^Note