Coldwater RAS in an Arctic charr farm in Northern Norway

Use of coldwater recirculating aquaculture systems (RAS) are still very rare in Norway, and only two farms are producing Arctic charr. This project took place in one of these commercial Arctic charr farms; Villmarksfisk AS in Bardu, Northern Norway.The farm gets its make-up water from ground water that holds 5 °C year around. Temperature in the rearing water varies between 7.5 °C (“low”) to 12 °C (“high”) through the year. The biological filter in the RAS seems to work stable at both “low” and “high” temperatures, including after incidents when feeding has been stopped for a day and started on top again the day after. Such an extreme change in loading was measured as a 70% increase in TAN concentration, with only minor changes in nitrite levels recorded. The biofilter also kept the nitrite stable and low in spite of diurnal variation in TAN excretion at normal feeding regimes (every day in three periods at day-time).The farming concept is to stock the farm with wild caught juvenile fish for on-growing to market size fish (0.75–1.00 kg). A drop in growth rate during early autumn has been a main concern for the farm. This may reflect a seasonal shift in growth potential, sometimes referred to as “autumn depression”. Interestingly, there is little sign of seasonal changes in the growth of hatchery-produced fish tested in the farm. Sampling of water quality through the seasons in tanks holding fish undergoing such growth depressions indicate that TAN excretion is much higher per kg feed used in the wintertime than in the springtime. This observation corresponds with the lack of weight gain during wintertime despite that the fish is feeding. Thus, feed conversion calculations indicate that feed utilization also varies with season reaching its nadir during this period.Both challenges concerning RAS in cold water and strongly reduced growth in autumn and winter time, have been investigated from 2005 to 2007 in a project financed by the Norwegian research council and the partners in the agricultural framework agreement.     

Sustained exercise improves vertebral histomorphometry and modulates hormonal levels in rainbow trout

Abnormal compressions and fusions of vertebral bodies are frequently observed in reared rainbow trout and could result from chronic and unbearable muscle pressures acting on the axial skeleton during intensive growth. Sustained swimming at moderate speeds was shown to induce many positive effects on growth and swimming performances in salmonids, but yet little is known about its effects on vertebral remodeling processes and related hormonal regulation. Rainbow trout were subjected to three different swimming speeds (0, 1.0 and 1.5 body length (BL) s^− 1), starting one month after they were first fed (65 mm) and ending when they reached 260 mm in size (market-size of 275 g). At the end of the experiment, 20 trout were sampled in each lot (N = 60) and blood samples were taken. Vertebrae abnormalities were assessed by radiological examinations. Vertebrae from the middle axial region (V32–38) were selected to evaluate bone mineralization (BM) and total bone area (Tt-B.Ar.) on radiographed transverse sections (125 ± 10 μm). Assays were performed to evaluate mineral homeostasis (calcemia and phosphatemia), bone cell activities (alkaline phosphatase, ALP, and tartrate-resistant acid phosphatase, TRAP) and bone regulating hormones (calcitonin, CT and thyroid hormones, THs). Sustained exercise reduced the appearance of fused vertebrae, enhanced vertebral BM and decreased vertebral Tt-B.Ar., while it increased circulating CT and TH levels. No variations were observed on mineral homeostasis and bone cell activities. Increasing the swimming speed up to 1.5 BL s^− 1 had positive effects on the vertebral skeleton, and therefore, seems to be a suitable approach to prevent aggravation of vertebral abnormalities in juvenile trout. The changes observed in vertebral features are interpreted as a compromise between the necessity to mobilize vertebral mineral ions in response to various physiological demands and to maintain vertebral strength against mechanical constraints.     

Effects of manganese on juvenile mulloway (Argyrosomus japonicus) cultured in water with varying salinity—Implications for inland mariculture

The effects of 5 mg/L of dissolved manganese on juvenile mulloway at salinities of 5, 15 and 45 ppt were determined by comparing their survival, growth and blood plasma and organ chemistry with those of fish grown at the same salinities without manganese addition. Survival of mulloway at 45 ppt in the presence of 5 mg/L of manganese (73 ± 13%) was significantly lower than all other treatments, which achieved 100% survival. Those fish grown in water without manganese exhibited rapid growth, which was not affected by salinity (SGR = 4.05 ± 0.29%/day). Those fish grown at 5 ppt and 45 ppt in the presence of manganese lost weight over the 2-week trial (SGR − 0.17 ± 0.42 and − 0.44 ± 0.83%/day, respectively), whilst those at 15 ppt gained some weight (SGR 1.70 ± 0.20%/day). Manganese accumulated in the gills, liver and muscle of the fish and significant differences in blood plasma chemistry were observed. Blood plasma sodium and chloride of fish exposed to manganese were significantly elevated in hyperosmotic salinity (45 ppt) and depressed at hyposmotic salinity (5 ppt) compared with unexposed fish at the same salinity; consistent with manganese causing apoptosis or necrosis to chloride cells. We did not, however, observe any gill epithelial damage under light microscopy. Blood plasma potassium was significantly elevated at all salinities in the presence of manganese and liver potassium and glycogen reduced. These findings are consistent with manganese interfering with carbohydrate metabolism.     

High dietary incorporation levels of rendered animal protein ingredients on performance of rainbow trout Oncorhynchus mykiss (Walbaum, 1972)

Two growth trials were conducted using spray-dried blood meal (BM), feather meal (FEM), meat and bone meal (MBM) and poultry by-product meal (PBM) as major protein sources in the diet of rainbow trout. In the first trial, five diets were formulated to examine the nutritive value of spray-dried BM and PBM. Increasing levels of BM (6, 12%) or PBM (10, 20, and 30%) replaced fish meal and corn gluten meal in the diet. For the second trial, eight diets were formulated to contain the following combinations: FEM + MBM, FEM + PBM or MBM + PBM. The diets containing FEM + MBM and FEM + PBM were supplemented with either L-lysine or DL-methionine, the amino acids predicted to be the two most limiting in these diets. Each experimental diet was allocated to three tanks of fish and fed for 20 weeks in the first trial or 16 weeks in the second trial. All the experimental diets were readily consumed by the fish and high growth and good feed efficiency ratio (FER) were achieved for all diets. In the first trial, there were no significant differences (P > 0.05) in weight gain or FER of fish fed the five experimental diets, suggesting that BM and PBM had high nutritive values for rainbow trout. In the second trial, growth of the fish fed the diet containing the FEM + PBM combination was not statistically different from growth of fish fed the control diet. Growth of fish fed diets with FEM + MBM or PBM + MBM combinations were slightly lower than that of fish fed the control diet. Supplementation of diets with either L-lysine or DL-methionine had no effect on the performance of the fish. The results from this study show that feather meal, poultry by-product meal, blood meal and meat and bone meal have good potential for use in rainbow trout diets at high levels of incorporation.     

Broad snouted caiman (Caiman latirostris) growth under different rearing densities

The effect of density on growth in body mass (BM) and total length (TL) of Caiman latirostris hatchlings raised in small pens (area 0.36 m²), for 3 months, was investigated. Twelve animals from each of three clutches were randomly distributed (1, 2 or 3 individuals) to two replicates at low rearing density (LRD: 0.12 m²/individual), medium rearing density (MRD: 0.06 m²/individual) and high rearing density (HRD: 0.04 m²/individual. Growth at LRD [BM: 150.75 ± 43.83 g (SE); TL: 11.58 ± 0.93 cm] and MRD (BM: 141.96 ± 22.55 g; TL: 8.38 ± 1.26 cm) was significantly more than at HRD (BM: 57.19 ± 14.38 g; TL: 4.61 ± 0.89 cm; p < 0.001). Density is important to achieving optimal growth and maintaining the well-being of C. latirostris in commercial ranching programs.     

Effects of emulsified versus saline administration of GnRHa on induction of ovulation in rainbow trout, Oncorhynchus mykiss

The effects of saline-dissolved or Freund's incomplete adjuvant (FIA)-emulsified GnRHa treatment on the induction of ovulation in rainbow trout, Oncorhynchus mykiss, were examined. The FIA-emulsified GnRHa was first diluted in 0.25 ml physiological saline and then mixed with an equal volume of FIA. Fish were selected in the beginning of the spawning season and were allocated into four groups and were treated intraperitoneally with (a) 0.5 ml of emulsified GnRHa (GnRHa–FIA), (b) 0.5 ml saline-dissolved GnRHa in a single injection (GnRHa-1), (c) 0.5 ml saline-dissolved GnRHa in two injections spaced 1 d apart (GnRHa-2) and (d) 0.5 ml of saline (Control). The GnRHa dose in all hormone treatments was 25 µg kg^− 1. All fish in the FIA–GnRHa and GnRHa-2 groups ovulated within 10 and 11 d after treatment, respectively. In contrast, only 75% in the Control fish and 60% of the fish in the GnRHa-1 group ovulated within 36 d after treatment. None of the treatments caused any pre- or post-spawning mortality in the broodstock. Fertilization, eyeing and hatching percentages of the produced progeny were normal in all the treatment groups and did not differ significantly among them. In conclusion, FIA-emulsified GnRHa can be effective in advancing the onset of and synchronizing the ovulation of rainbow trout within a two-week period, thus shortening the egg collection period, without affecting broodstock survival and egg quality.     

Evaluation of brook trout production in a coldwater recycle aquaculture system

Brook trout (Salvelinus fontinalis) are a commercially important coldwater species reared in Wisconsin and the Midwestern United States. Brook trout are raised by private, tribal, state, and federal fish hatchery facilities in Wisconsin. Approximately 10% of private coldwater aquaculture operations are presently raising brook trout of various strains for stocking uses and a limited amount for food markets. Growing brook trout to a larger size, if they can be reared in a shorter time span, may present a potential new sector for the aquaculture market in the Midwestern US. The present study reports hatchery production attributes, i.e., growth, survival, fin condition, feed efficiency, water chemistry requirements and general husbandry of Lake Superior strain (Nipigon) brook trout reared in a recirculating aquaculture system (RAS), operated at an average temperature of 13 °C. The recycle system at NADF reared 1379 kg of brook trout over a 10-month period from fingerling (9 g) to market size (340–454 g). The trout grew faster (0.84 g/day and 0.64 mm/day) in the RAS than fish cultured in traditional flow-through tank culture utilizing ground water at 7.6 °C (0.14 g/day and 0.35 mm/day). Final average weight of RAS fish was 260 g, while the flow-through fish averaged 65 g. Final tank densities for the RAS averaged 40.4 kg/m³ while flow-through tanks averaged 31.2 kg/m³. Throughout the project, feed conversions in the RAS ranged from 0.9 to 1.3. Water quality variables such as TAN, nitrite, DO, temperature, TSS, CO₂, ph, etc. were within safe limits for brook trout and will be discussed. It does appear from this initial research project that market size brook trout can be raised successfully in a recycle system within a similar time frame as a rainbow trout produced in a Wisconsin typical flow-through facility.     

Long‐term epidemiological survey of Kudoa thyrsites (Myxozoa) in Atlantic salmon (Salmo salar L.) from commercial aquaculture farms

Kudoa thyrsites (Myxozoa) encysts within myocytes of a variety of fishes. While infected fish appear unharmed, parasite‐derived enzymes degrade the flesh post‐mortem. In regions of British Columbia (BC), Canada, up to 4–7% of fillets can be affected, thus having economic consequences and impacting the competitiveness of BC's farms. K. thyrsites was monitored in two farms having high (HP) or low (LP) historical infection prevalence. At each farm, 30 fish were sampled monthly for blood and muscle during the first year followed by nine samplings during year two. Prevalence and intensity were measured by PCR and histology of muscle samples. In parallel, fillet tests were used to quantify myoliquefaction. Infections were detected by PCR after 355 and 509 degree days at LP and HP farms, respectively. Prevalence reached 100% at the HP farm by 2265 degree days and declined during the second year, whereas it plateaued near 50% at the LP farm. Infection intensities decreased after 1 year at both farms. Blood was PCR‐positive at both farms between 778 and 1113 degree days and again after 2000 degree days. This is the first monitoring project in a production environment and compares data between farms with different prevalence.     

Relationship between sea lice levels on sea trout and fish farm activity in western Scotland

The relationship between aquaculture and infestations of sea lice on sea trout, Salmo trutta L., is controversial. Here, the association between sea lice infestations on wild sea trout and characteristics of local Atlantic salmon, Salmo salar L., farms were investigated using data collected on the Scottish west coast. The proportion of sea trout with louse burdens above a critical level was positively related to the fork length of the sea trout and the mean weight of salmon on the nearest fish farm, and negatively related to the distance to that farm. The distance to the nearest fish farm did not influence the probability of infestations above the critical level beyond 31 km although there was considerable uncertainty around this cut‐off distance (95% limits: 13–149 km). The results support a link between Atlantic salmon farms and sea lice burdens on sea trout in the west of Scotland and provide the type of information required for marine spatial planning.     

Low optimal temperatures for food conversion and growth in the big-headed turtle, Platysternon megacephalum

We held juvenile big-headed turtles, Platysternon megacephalum, from eastern China, at temperatures from 20 to 29.4 °C to determine effects on feeding, growth and food conversion. Food intake increased significantly from 20 to 22.4 °C, remained high until 27.1 °C, and then decreased dramatically at 29.4 °C. Digestive efficiency for energy decreased as temperature increased, whereas the digestive efficiency of protein increased from 20 to 25 °C, and decreased at higher temperatures. The relationships between specific growth rate (SGR), food conversion coefficient (C_c) and temperature (T) were curvilinear, and could be described by quadratic equations: SGR = −0.01 T² + 0.47 T − 5.24 and C_c = −0.37 T² + 17.20 T − 181.85. Maximum growth was estimated to occur at 23.9 °C, with 90% of the maximum being achieved within the range of 21.9–25.8 °C; maximal food conversion occurred at 23.2 °C, with a 90% range from 21.0 to 25.4 °C. The temperature range (22–25 °C) found to promote best growth and food conversion in juvenile P. megacephalum is lower than for many other freshwater turtles. Temperatures of 22–25 °C are recommended for use in culture of this species to maximize growth and food conversion.     

RRR-α-Tocopheryl succinate is a less bioavailable source of vitamin E than all-rac-α-tocopheryl acetate for red drum, Sciaenops ocellatus

Bioavailability of the succinate ester of α-tocopherol has never been investigated with aquatic animals to date. Therefore, a 12-week feeding trial was conducted to compare bioavailability of α-tocopheryl acetate and α-tocopheryl succinate by slope ratio analysis. The semi-purified diets were supplemented with either 0 (basal), 10, 20 and 40 IU vitamin E/kg as all-rac-α-tocopheryl acetate or 10, 20, or 40 IU vitamin E/kg as RRR-α-tocopheryl succinate. Red drum juveniles were conditioned by feeding the basal diet for 8 weeks prior to the experimental period to reduce whole-body tocopherols. Fish initially averaging 12.2 ± 0.4 g/fish (mean ± SD) were fed experimental diets at a rate approaching apparent satiation for 12 weeks. Weight gain and feed efficiency responses of fish fed diets were not significantly altered by the type or level of vitamin E supplemented. However, α-tocopherol levels in liver and plasma were significantly (P < 0.01) influenced by dietary vitamin E level and ester form. The liver retention of α-tocopheryl acetate was 14 times higher than α-tocopheryl succinate, while thiobarbituric acid reactive substances (TBARS) in liver of fish fed α-tocopheryl acetate tended to be (P < 0.1) lower than that of fish fed α-tocopheryl succinate. In addition, plasma ascorbic acid in fish fed graded levels of α-tocopheryl acetate was significantly higher than fish fed graded levels of α-tocopheryl succinate. Fish fed the basal diet and 10 IU α-tocopheryl succinate/kg showed edema in the heart, while fish fed all other diets did not exhibit this pathology. Within the dose range of 0–40 IU/kg diet, hematocrit, neutrophil oxidative radical production and intracellular superoxide anion production of head kidney macrophages were not significantly influenced by α-tocopherol ester or dietary supplementation level. In conclusion, α-tocopheryl succinate is not readily available to juvenile red drum compared to the widely used α-tocopheryl acetate.     

Preliminary study for description of bone tissue responsiveness to prolonged dietary phosphorus deficiency in rainbow trout,Oncorhynchus mykiss (Walbaum)

Prolonged dietary phosphorus (P) deficiency induces a generalized demineralization of bone tissues; however, the differential responsiveness of the diverse tissues to P deficiency remains unknown. Triploid all‐female juvenile rainbow trout (initial mass ~60 g) were fed two practical diets (0.26% and 0.52% digestible P for P‐deficient and P‐sufficient diets) until P‐sufficient fish reached 850 g (241 days; 12°C; 18:6 D:L). Early P‐deficient fish were fed from day 0 the low P‐diet, while late P‐deficient only started feeding at day 134. Growth performance was assessed monthly and carcass samplings were performed at day 0, 134 and 241 to assess mineralization characteristics of different tissues. Ash and content of phosphorus, calcium and magnesium of scales, operculae, ribs and vertebrae as well as the occurrence of abnormalities in ribs and vertebrae were assessed. The tissues most affected by P deficiency were: vertebrae > scales > opercula > ribs. P deficiency affects bone tissues differentially based on the physiological and biomechanical roles of the tissues. As scales were found to be a better indicator to predict abnormalities, understanding of scale metabolism could facilitate P status estimation in fish.     

Long-term culture of Atlantic salmon (Salmo salar L.) in submerged cages during winter affects behaviour, growth and condition

In the search for alternative farming methods, we investigated whether large salmon submerged below 10 m in winter conditions behaved normally and performed as well as control fish held in standard surface cages. On average, 2345 salmon of ~ 3.5 kg were kept in each of six 2000 m³ sea-cages for 6 weeks; three of which were submerged to 10–24 m depth and three acted as surface controls (0–14 m). Behaviour during both day and night was studied with echo-sounders, and underwater video cameras fitted with infra-red lamps. A sub-sample of fish from each cage was weighed, measured and assessed for fin and snout condition prior to and after the experimental period. In addition, the vertebral column of 50 fish from the control and submerged treatments were dissected and X-rayed to assess vertebral deformities. The submerged salmon seemed unable to re-fill any gas into the swim bladder, as a linear decrease in echo reflection to < 5% of pre-submergence levels after 22 days of submergence indicated loss of almost all gas from the physostomous swim bladders and negatively buoyant fish. Around day 22, submerged salmon swam at night time with a distinct ‘tail-down, head-up’ tilt (26°) compared to the horizontal swimming position of control fish (− 3°). Average swimming speed (body length per second) of submerged salmon were 1.3–1.4 times faster (day: 0.77 ± 0.02; night: 0.46 ± 0.02, (mean ± SE)) than control fish (day: 0.54 ± 0.01; night: 0.37 ± 0.02) both during day and night. Almost no mortality was seen, and the submerged salmon maintained similar diurnal vertical migrations as the surface fish, indicating that deep submergence did not exhaust the fish. However, submerged fish fed less efficiently, resulting in lower growth and reduced feed utilization. Fins and snouts of the submerged fish had small, but significantly more erosion than the control fish. Vertebrae in the tail region were significantly compressed in the submerged fish compared to control fish. This could be an early symptom of development of vertebral deformities. The results suggest that continuous submergence below 10 m for longer than 2 weeks reduces the welfare and performance of Atlantic salmon.     

Development of cryopreservation for maintaining yellow catfish Pelteobagrus fulvidraco sperm

Yellow catfish (Pelteobagrus fulvidraco) is a candidate freshwater fish for aquaculture in China with its high consumer demand. The aim of this study was to examine the possibility of storage of the sperm of yellow catfish by cryopreservation in liquid nitrogen. Experiments were designed to investigate the effects of the different combinations of three extenders (Ringer extender, Kurokura-1 extender and D-15 extender) and three cryoprotectants (DMSO, Glycerol and Methanol) on the cryopreservation of yellow catfish sperm. Post-thaw sperm motility, fertilization and hatching rate were detected to evaluate the reliability of sperm cryopreservation. The results demonstrated that Ringer extender and 10% methanol was the best combination for protecting the sperm during freezing in liquid nitrogen by a three-step method and thawing in a water bath at 37 °C for 60 s. In this combination for cryopreservation, sperm maintained the highest post-thaw motility (65 ± 5%), fertilization (90.47 ± 3.67%) and hatching rate (88 ± 4%). And more interestingly, the fertilization and hatching rate were similar to those of fresh sperm (97.55 ± 2.74% and 92 ± 5%). Successful sperm cryopreservation techniques for yellow catfish have been developed for hatchery purpose.     

The effect of temperature on the growth, survival and food consumption of the east coast rock lobster Panulirus homarus rubellus

The successful culture of the east coast rock lobster Panulirus homarus rubellus is reliant, among other factors, on the provision of optimal water quality for growth and survival. This study investigated the effect of temperature over a range of 9.7 °C (18.9 ± 0.7 °C to 28.6 ± 1.5 °C) on the growth and survival of juvenile (40.4 ± 9 mm CL; 63.64 ± 12.05 g) P. h. rubellus fed a diet of fresh mussel flesh. Specific growth rate (SGR) was significantly different between temperatures (p = 0.01), with the highest values recorded for the 24 and 28 °C treatments. There was no significant difference in moult increment (MI) between temperatures in terms of both an increase in weight (p = 0.83) and carapace length (p = 0.54). Intermoult period (IMP) differed significantly between temperatures (p = 0.0015) with mean IMP lowest at 24 °C, although not significantly different from the means of the 26 and 28 °C treatments. IMP was highest at 19 and 21 °C. Apparent feed intake was significantly different between treatments (p < 0.0001) and exhibited a strong positive correlation with increasing temperature (y = − 1.67 + 0.16x ; r² = 0.81). Food conversion ratio (FCR) differed significantly between temperatures (p = 0.02) with 24 °C exhibiting the most efficient FCR. Results indicate that efficient growout of juvenile P. h. rubellus, in terms of both growth and food conversion efficiency, is obtainable at 24 °C.     

Occurrence and prevalence of infectious pancreatic necrosis virus in rainbow trout (Oncorhynchus mykiss) cultured in cages in the Black Sea

Rainbow trout (Oncorhynchus mykiss) cultured in cage systems in the South Eastern Black Sea were surveyed for the type, occurrence and prevalence of infectious pancreatic necrosis virus (IPNV). Two nearby farms (designated as Farm A and Farm B) were visited monthly in 2007 and 2008. At each farm, 385 fish were selected randomly from five cages. Another farm with infected trout from a hatchery also was monitored for IPNV from the transfer to harvest. IPNV was found to be prevalent in both farms surveyed. In Farm A, IPNV was present throughout the growing period, from January to May, and all five randomly sampled cages tested positive for IPNV in March and April of 2007. In Farm B, IPNV was present only in February and March in 2007, and in 2008, IPNV was observed in January (two cages) and February (one cages) at low levels. Interestingly, IPNV was absent 2 weeks after transfer to the sea at 17.5°C. The same strain of IPNV, genotype III that was isolated from the same stock of fish at the hatchery, reoccurred when water temperatures dropped to 12°C in December in the Black Sea. Transferring fish to the sea at high water temperatures could lessen the negative impacts of IPNV on growth of rainbow trout in brackish water.     

Prediction of apparent protein digestibility of ingredients and diets by in vitro pH-stat degree of protein hydrolysis with species-specific enzymes for juvenile Pacific white shrimp Litopenaeus vannamei

Aquafeed production faces global issues related to availability of feed ingredients. Feed manufacturers require greater flexibility in order to develop nutritional and cost-effective formulations that take into account nutrient content and availability of ingredients. The search for appropriate ingredients requires detailed screening of their potential nutritional value and variability at the industrial level. In vitro digestion of feedstuffs by enzymes extracted from the target species has been correlated with apparent protein digestibility (APD) in fish and shrimp species. The present study verified the relationship between APD and in vitro degree of protein hydrolysis (DH) with Litopenaeus vannamei hepatopancreas enzymes in several different ingredients (n = 26): blood meals, casein, corn gluten meal, crab meal, distiller's dried grains with solubles, feather meal, fish meals, gelatin, krill meals, poultry by-product meal, soybean meals, squid meals and wheat gluten. The relationship between APD and DH was further verified in diets formulated with these ingredients at 30% inclusion into a reference diet. APD was determined in vivo (30.1 ± 0.5 °C, 32.2 ± 0.4‰) with juvenile L. vannamei (9 to 12 g) after placement of test ingredients into a reference diet (35 g kg^− 1 CP; 8.03 g kg^− 1 lipid; 2.01 kcal g^− 1) with chromic oxide as the inert marker. In vitro DH was assessed in ingredients and diets with standardized hepatopancreas enzymes extracted from pond-reared shrimp. The DH of ingredients was determined under different assay conditions to check for the most suitable in vitro protocol for APD prediction: different batches of enzyme extracts (HPf5 or HPf6), temperatures (25 or 30 °C) and enzyme activity (azocasein): crude protein ratios (4 U: 80 mg CP or 4 U: 40 mg CP). DH was not affected by ingredient proximate composition. APD was significantly correlated to DH in regressions considering either ingredients or diets. The relationships between APD and DH of the ingredients could be suitably adjusted to a Rational Function (y = (a + bx)/(1 + cx + dx²), n = 26. Best in vitro APD predictions were obtained at 25 °C, 4 U: 80 mg CP both for ingredients (R² = 0.86; P = 0.001) and test diets (R² = 0.96; P = 0.007). The regression model including all 26 ingredients generated higher prediction residuals (i.e., predicted APD − determined APD) for corn gluten meal, feather meal, poultry by-product meal and krill flour. The remaining test ingredients presented mean prediction residuals of 3.5 points. A model including only ingredients with APD > 80% showed higher prediction precision (R² = 0.98; P = 0.000004; n = 20) with average residual of 1.8 points. Predictive models including only ingredients from the same origin (e.g., marine-based, R² = 0.98; P = 0.033) also displayed low residuals. Since in vitro techniques have been usually validated through regressions against in vivo APD, the DH predictive capacity may depend on the consistency of the in vivo methodology. Regressions between APD and DH suggested a close relationship between peptide bond breakage by hepatopancreas digestive proteases and the apparent nitrogen assimilation in shrimp, and this may be a useful tool to provide rapid nutritional information.     

Salinity effects on reproduction of giant freshwater prawn Macrobrachium rosenbergii (de Man)

Understanding the role of salinity in breeding and growth has the potential to enhance production of giant freshwater prawn, Macrobrachium rosenbergii. This study investigated the reproduction of females reared in salinities of 0, 6, 12, and 18 g L^− 1. Mean weight of females decreased with increased salinity (31.40 ± 1.54, 25.14 ± 1.16, 20.80 ± 0.81, and 16.62 ± 1.04 g at 0, 6, 12, and 18 g L^− 1, respectively). Larval production was delayed by 2 months in females reared in 12 g L^− 1 compared to 6 and 0 g L^− 1 and the cumulative number of berried females decreased with increased salinity. The number of larvae produced was positively correlated to weight of female. A larval production not only differed between salinity treatments, but also that larval production per gram of female differed between treatments. Females reared in lower salinity of 0 and 6 g L^− 1 produced larger numbers of larvae (12,155 ± 480 and 6519 ± 323, respectively) compared to 12 and 18 g L^− 1 (3751 ± 256 and 0, respectively). The number of larvae produced per gram of female was inversely related to the salinity levels (Y = − 37.54X + 685.65, n = 339, r² = 0.995, p < 0.05). Survival of larvae from females reared at 0 and 6 g L^− 1 was higher than those from females reared in 12 g L^− 1. This study clearly shows that female broodstock reared in lower salinity was larger, reproduced early, and produced more offspring than at higher salinity and this could significantly impact coastal prawn culture where seasonal fluctuation of salinity in the hatchery is common.     

Non‐specific cellular defence mechanisms of rainbow trout (Oncorhynchus mykiss) in intensive and extensive rearing technologies

Water as a habitat is highly variable in terms of the physico‐chemical properties. The aim of the studies was to analyze the quality of the technology by evaluating the non‐specific cellular defence potential of rainbow trout (Oncorhynchus mykiss) in diversified intensity culture systems and in different periods of the breeding cycle. The evaluation was conducted in order to establish the scientific basis for the development of principles for recognition of the culture of this species as ‘organic’. Six rainbow trout rearing farms were selected for the studies and divided into two equal groups according to the production technology: farms with a flow through system (with single water usage – OOH) and facilities with multiple water usage via its backflow (re‐circulating system – RAS). The samples for tests were taken from 20 individuals from each fish farm. In all fish that originated both from OOH‐type farms and RAS operations, an increase in the activity of non‐specific cellular immunity in the autumn was observed. Statistically significant reduction in the activity of cellular defensive mechanisms in small (300–500 g) and big (501–850 g) fish occurred on two 3‐OOH and 3‐RAS farms in spring and autumn in 2011. During these periods, the research has shown the presence of Infectious Pancreatic Necrosis Virus (IPNV), which provoked an immune suppression. Based on the obtained results it is concluded that there were no significant differences in the parameters of non‐specific cellular immunity in rainbow trout originating from different farming systems OOH and RAS.