Age-specific patterns in density-dependent growth of white crappie, Pomoxis annularis

The relationship between growth in white crappie, Pomoxis annularis Rafinesque, and climate, lake morphometry and population density was studied in 103 Texas reservoirs. Growth of age‐0 through age‐3 white crappie was significantly (P≤0.05) related to latitude, growing season and surface area. Growth of age‐1 through age‐5 white crappie also was related to annual precipitation. Multiple linear regression models with precipitation and mean catch per unit effort (CPUE) of white crappie as independent variables explained 14–22% of the variation in growth of age‐0, ‐1 and ‐2 white crappie. By contrast, growth of age‐3, ‐4 and ‐5 white crappie was unrelated to CPUE. Apparently, between age 2 and 3, the density of white crappie in Texas reservoirs falls below a density‐dependent growth threshold beyond which growth is no longer related to density. This density‐dependent threshold was most likely related to angler harvest of larger, older white crappie.     

Protein metabolism during sexual maturation in female Atlantic salmon (Salmo salar L)

Body composition and fractional rates of protein synthesis (percentage of the protein mass synthesized per day) were determined in female Atlantic salmon returning to the River Tay, Scotland in July and in October after a 95 day period without food, during which time the animals became sexually mature. During the 95 day period of starvation/sexual maturation the ventricle and red muscle remained as a constant proportion of fresh weight whereas the liver, gill and ovary increased and the stomach and white muscle decreased. Fractional rates of protein synthesis increased markedly in the liver, stomach and ovary during the period of starvation/sexual maturation. In the gill, ventricle and white muscle fractional protein synthesis rates increased slightly or remained constant. From the estimated rates of protein loss or gain in the various tissues it is concluded that there is considerable protein turnover and repartitioning of amino acids during the period of starvation and sexual maturation. The absolute rate of protein synthesis rates in the ovary indicates that this tissue made the largest contribution to the energy and amino acid demands of the fish, whilst most of the amino acids required for maturation of the ovary were derived from white muscle, principally as the result of increased muscle protein degradation.     

Population ecology and prey consumption by fathead minnows in prairie wetlands: importance of detritus and larval fish

Abstract –  The fathead minnow Pimephales promelas occurs in high densities in wetlands of the prairie pothole region (PPR) of North America, but food resources sustaining these populations are poorly known. We assessed population dynamics and prey consumption of fathead minnow populations in three PPR wetlands for 2 years. Fish density peaked at 107 fish per m² for all age classes combined. Larval and juvenile fish dominated these populations in terms of abundance and accounted for 83% of total prey consumption. Detritus dominated fish diets, representing 53%, 40% and 79% of diet mass for larval, juvenile and adult fish respectively. Detritus consumption was positively related to minnow density and negatively related to invertebrate abundance, but only for adult fish. Seasonal production:biomass ratios were unrelated to proportions of detritus in the diet for all ages of fish, indicating that detritus is an important food resource capable of meeting metabolic demands and sustaining fish growth in high-density populations. Detritus consumption may also weaken links between abundance of invertebrate prey and minnows, promoting dense fish populations with strong, consistent influences on wetland ecosystems.     

Stocking density and artificial habitat influence stock structure and yield from intensive nursery systems for mud crabs Scylla serrata (Forsskål 1775)

Intensive nursery systems are designed to culture mud crab postlarvae through a critical phase in preparation for stocking into growout systems. This study investigated the influence of stocking density and provision of artificial habitat on the yield of a cage culture system. For each of three batches of postlarvae, survival, growth and claw loss were assessed after each of three nursery phases ending at crab instars C1/C2, C4/C5 and C7/C8. Survival through the first phase was highly variable among batches with a maximum survival of 80% from megalops to a mean crab instar of 1.5. Stocking density between 625 and 2300 m⁻² did not influence survival or growth in this first phase. Stocking densities tested in phases 2 and 3 were 62.5, 125 and 250 m⁻². At the end of phases 2 and 3, there were five instar stages present, representing a more than 20‐fold size disparity within the populations. Survival became increasingly density‐sensitive following the first phase, with higher densities resulting in significantly lower survival (phase 2: 63% vs. 79%; phase 3: 57% vs. 64%). The addition of artificial habitat in the form of pleated netting significantly improved survival at all densities. The mean instar attained by the end of phase 2 was significantly larger at a lower stocking density and without artificial habitat. No significant effect of density or habitat on harvest size was detected in phase 3. The highest incidence of claw loss was 36% but was reduced by lowering stocking densities and addition of habitat. For intensive commercial production, yield can be significantly increased by addition of a simple net structure but rapidly decreases the longer crablets remain in the nursery.     

Evaluation of two soybean meals fed to yellow perch (Perca flavescens)

Aquaculture of yellow perch (Perca flavescens) has been increasing, yet there have been few nutritional studies and no evaluations of alternative protein sources in diets. Solvent‐extracted, dehulled soybean meal (SBM) and expelled‐extruded soybean meal (exSBM) were fed to yellow perch to evaluate their effectiveness in replacing dietary fish meal (FM) in isonitrogenous practical feed formulations. Both soy ingredients were incorporated in graded amounts from 100 to 730 g kg⁻¹ of the diet. Feed consumption, weight gain, feed efficiency (FE) and survival were significantly affected by type of soy ingredient, concentration and the interaction of the two main effects. Consumption was significantly lower in fish fed diets containing 400, 600 and 730 g kg⁻¹ compared to fish fed diets containing lower concentrations. Weight gain was significantly lower in fish fed diets containing 600 g kg⁻¹ and FE significantly lower in fish fed diets containing 500 g kg⁻¹ compared to fish fed the control diet or lower concentrations of soy ingredients. Most fatty acid concentrations were affected by feeding exSBM compared to fish fed the control diet, but long chain fatty acids remained at relatively high concentrations. Based on feed consumption, weight gain and FE data, yellow perch are able to effectively utilize both soy ingredients in practical diets. A conservative recommendation of 300 g kg⁻¹ diet appears appropriate for growout diets.     

Effect of different methods for the induction of spermiation on semen quality in European eel

Five hormonal treatments with human chorionic gonadotropin (hCG) were tested for the induction of maturation and spermiation in male farmed eels. The main aim was to optimize previously used hormonal treatments to achieve shorter induction treatments, longer spermiation periods and/or higher sperm quality. Fish treated for just 3 weeks (treatment E) or until the onset of spermiation (treatment C) showed the worst results, while the treatment consisting of weekly administration of 1.5 IU hCG g^?1 fish (treatment A) induced the highest percentage of spermiating males, the highest number of sperm samples and sperm volumes and densities similar to the rest of the treatments (B: half hormone dosage, or D: biweekly administration). Evaluation of the sperm quality was performed by computer‐assisted sperm analysis (CASA), considering the percentage of total motile spermatozoa, the percentage of fast and medium‐velocity spermatozoa, as well as different motility parameters. Sperm samples from A‐D groups showed between 44% and 54% motile spermatozoa, and between 10% and 15% fast spermatozoa, while samples from E‐treated males showed 0% motile cells. No significant differences were found in the spermatozoa straight line velocity (VSL), curvilinear velocity (VCL) or the angular velocity (VAP), neither spermatozoa beating cross frequency (BCF) between A–D groups.     

Influence of larval co-feeding with live and inert diets on weaning the tongue sole Cynoglossus semilaevis

The tongue sole Cynoglossus semilaevis, an inshore fish in China, has showed great potential in aquaculture recently. However, poor survival was recorded during the period of weaning from live Artemia to artificial diets. In this paper, the influence of co‐feeding larvae with live and inert diet on weaning performance was described. The C. semilaevis larvae were reared at 21 ± 1 °C and fed four different feeding regimes from 6 days post‐hatching (dph): A, Artemia (10 individuals mL^?1); B, Artemia (5 individuals mL^?1); C, mixed diet (10 Artemia individuals mL^?1 and 12 mg L^?1 inert diet); and D, mixed diet (5 Artemia individuals mL^?1 and 12 mg L^?1 inert diet). Rotifers were also supplied in all cases during the first days of feeding. Mixed diets of commercial formulated feed and live prey (rotifers and Artemia) allowed larvae to complete metamorphosis, achieving similar specific growth rate (SGR) (18.5 ± 1.4% and 18.7 ± 1.6%) and survival (40 ± 7.6% and 48.5 ± 6.8%) compared with larvae fed on live feed alone (SGR of 18.3 ± 1.2%, 19.3 ± 1.9% and survival of 41.2 ± 11.3%, 38 ± 4.9%). However, in metamorphosed fish, when live feed was withdrawn on 31 dph, there was significant difference (P < 0.05) in survival and growth among treatments. Metamorphosed fish, previously fed mixture diets during larval stages, had similar survival (62.1 ± 7.6% and 62.8 ± 3.9% for regimes C and D, respectively) but higher than that obtained for fish that previously fed on live feed (49.3 ± 2% and 42.1 ± 3.9% for regimes A and B, respectively) after weaning (day 60). The SGR of weaned fish previously fed live feed was similar (3.1 ± 0.6% and 2.92 ± 0.6% for regimes A and B, respectively) but lower than that recorded for fish that was fed from day 6 to day 30 on the mixed diet (4.5 ± 1.1% and 4.9 ± 0.3% for regimes C and D, respectively). It is suggested that weaning of C. semilaevis from early development would appear to be feasible and larval co‐feeding improves growth and survival.     

Amoebic gill disease: sequential pathology in cultured Atlantic salmon, Salmo salar L

Amoebic gill disease (AGD) affects the marine culture phase of Atlantic salmon, Salmo salar L., in Tasmania. Here, we describe histopathological observations of AGD from smolts, sampled weekly, following transfer to estuarine/marine sites. AGD was initially detected histologically at week 13 post-transfer while gross signs were not observed for a further week post-transfer. Significant increases (P < 0.001) in the proportion of affected gill filaments occurred at weeks 18 and 19 post-transfer coinciding with the cessation of a halocline and increased water temperature at the cage sites. The progression of AGD histopathology, during the sampling period, was characterized by three phases. (1) Primary attachment/interaction associated with extremely localized host cellular alterations, juxtaposed to amoebae, including epithelial desquamation and oedema. (2) Innate immune response activation and initial focal hyperplasia of undifferentiated epithelial cells. (3) Finally, lesion expansion, squamation-stratification of epithelia at lesion surfaces and variable recruitment of mucous cells to these regions. A pattern of preferential colonization of amoebae at lesion margins was apparent during stage 3 of disease development. Together, these data suggest that AGD progression was linked to retraction of the estuarine halocline and increases in water temperature. The host response to gill infection with Neoparamoeba sp. is characterized by a focal fortification strategy concurrent with a migration of immunoregulatory cells to lesion-affected regions.     

Isolation of a highly pathogenic Vibrio pelagius strain associated with mass mortalities of turbot,Scophthalmus maximus (L.), larvae

A bacterial strain, characterized as Vibrio pelagius (Hq 222), was isolated from a turbot, Scophthalmus maximus (L.), larvae mass mortality in a commercial fish farm in Spain. Turbot larvae, post-larvae (0.2 g) and juveniles (5 and 15 g) were experimentally infected. The bacterium appeared to be very virulent for larvae and post-larvae, LD50 being < 5 bacteria mL(-1) for larvae 1 week post-infection and 3.9 x 10(5) bacteria mL(-1) in post-larvae at day 12 post-infection. The bacterial strain was recovered in pure culture from the internal organs of infected fish. Histological lesions in post-larvae exhibited swelling and necrosis of gill secondary lamellae, sloughing of intestinal mucosa and necrosis of haematopoietic tissue in the kidney. Vibrio pelagius (Hq 222) was able to grow in sterile sea water when incubated at room temperature or at 15 degrees C. Vibrio pelagius (Hq 222) was more adherent to the turbot cell lines TV-1 and TF than Escherichia coli. In both cell lines, the number of adhered bacteria increased with incubation time.