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.     

Water quality and rainbow trout performance in a Danish Model Farm recirculating system: Comparison with a flow through system

The objective was to compare water quality and fish growth and mortality in a pilot scale recirculating system (RS) and a control tank in flow through system (FTS). The RS was designed after the Danish Model Trout Farm and operated with a make up water renewal rate of 9 m³ kg^-1 of fish produced. RS water quality did not decrease significantly with water flow rate decrease in the RS. During the experiment, the RS water treatment system presented solids removal efficiency of 59.6 ± 27.7% d⁻¹, ammonia oxidation of 45 ± 32 g m⁻³ d⁻¹, oxygenation yield of 392 ± 132 g of O₂ kWh⁻¹ and CO₂ degassing of 23.3 ± 11.9% pass⁻¹. In the RS, nitrite concentration was 0.15 ± 0.07 mg l⁻¹, close to the toxicity threshold; a N₂ supersaturation phenomenon was measured, probably due to the air injection depth. The biofilter and sedimentation area management has to be improved to avoid organic matter decomposition and release of dissolved elements. Even if no N₂ over-saturation apparent effect on fish performance and aspect were detected, the airlift depth has to be modified in the case of industrial development of the RS. Some improvements of the water treatment system, especially on the airlift and sedimentation area, are suggested.Concerning fish growth, no significant differences were observed between the RS and the FTS. No pathologies were detected and cumulative mortality rates (0.1%) were similar to the farm's usual data. There were no significant effects of water flow rate decrease in the RS on fish performance and energy savings were recorded to be 0.7 kWh kg⁻¹ of fish produced between RS₁ and RS₂. The global energy cost of the RS was 3.56 kWh kg⁻¹ of fish produced (0.107 € kg⁻¹ of fish produced). Even if the energy consumption of the water treatment system can be improved, the results confirm that recirculating system can be used for industrial trout on growing, without fish performance deterioration.     

Phosphorous (P) deficiency due to low P availability in fishmeal produced from blue whiting (Micromesistius poutassou) in feed for under-yearling Atlantic salmon (Salmo salar) smolt

Seawater transferred under-yearling Atlantic salmon (120 g) were fed a practical fishmeal formulated diet containing 57.4% blue whiting fishmeal and providing 15 g kg^− 1 total phosphorous (P) in the diet. The basal diet was supplemented with graded dietary levels of inorganic P (0, 3, 6, 9, 12 and 15 g kg^− 1) to total P levels of 15, 18, 21, 24, 27 and 30 g kg^− 1. Within a feeding period of 12 weeks, classical signs of P deficiency developed in Atlantic salmon fed the P un-supplemented diet containing 15 g kg^− 1 total P of natural origin. Deficiency signs included reduced growth and feed efficiency, reduced tissue mineral concentration (P, Ca, Mg, Zn), increased P:Ca ratio in the body, increased condition factor, metabolic disorder as indicated by lipid accumulation and impaired protein utilization, as well as reduced lipid, energy and Zn digestibility. Supplementation of inorganic P-salts in the diet at 3 g kg^− 1 (18 g kg^− 1 total P) significantly improved the production results with respect to growth and feed efficiency, and restored all other signs of P deficiency in fish. A higher supplementation level of 6 g kg^− 1 inorganic P (21 g kg^− 1 total P) was required for optimal mineralization in whole body and vertebrae. The highest supplementation levels of 15 g kg^− 1 added inorganic P (30 g kg^− 1 total P) seemed to increase P excretion and to have slightly negative impacts on growth and bone mineralization. Results suggest that P availability from blue whiting fishmeal is very low (3.2 g kg^− 1) and inadequate to meet dietary P requirement in rapidly growing under-yearling salmon immediately following seawater transfer, despite high natural P content in the blue whiting fishmeal.     

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.     

Effect of feeding apidaecin on common carp (Cyprinus carpio) growth performances and immune function

Effect of apidaecin on common carp (Cyprinus carpio) based on growth performance, feed utilization (Feed Conversion Ratio, FCR) and immune parameters were investigated. Twelve aquaria with three replicates for G1-3 and control were used. The synthesized apidaecin peptide was added to common carp basal diets (Control) as additives in three concentrations: 10.0 mg kg^− 1 (G1), 15.0 mg kg^− 1 (G2) and 30.0 mg kg^− 1 (G3) by wet weight of basal diet. After an 80-day feeding experiment, G2 and G3 showed significantly better (P < 0.05) results of growth performances and FCR than the control. However, there was no remarkable difference (P > 0.05) between G2 and G3. As for G1, the final weight, SGR (Specific Growth Rate) and DG (Daily Gain) were increased and the FCR was decreased, but not significantly (P > 0.05) compared with the control. The serum lysozyme activity of G2 and G3 was significantly increased (P < 0.05) than the control. As for the alternative complement pathway activity, G2 and G3 were also higher (P < 0.05) than the control. However, no significant difference (P > 0.05) was found whichever between G2 and G3 or between G1 and G2 in both lysozyme and the alternative complement pathway activities. Furthermore, there was no remarkable difference between G1 and the control in immune parameters.     

Influence of duration of aeration on growth and survival of carp fingerlings during high density seed rearing

Impact of varied durations of aeration on growth, survival and production performances of catla (Catla catla), rohu (Labeo rohita), fringe lipped carp (Labeo fimbriatus) and olive barb (Puntius sarana) were evaluated in outdoor concrete tanks (10 m × 5 m × 1.3 m) during fingerlings rearing. At a combined stocking density of 0.5 million fry/ha, provision of night time aeration for 4, 8 and 12 h was evaluated as the three treatments, T-I, T-II and T-III, respectively against control (T-c, without aeration). Overall survival and net biomass of the species increased among the treatments significantly as a function of aeration hours (T-c < T-I < T-II < T-III). Aeration for 8 and 12 h showed significantly higher survival, harvested body weight and SGR in all the carps than those with 4 h (T-I) and no aeration (T-c), suggesting 8–12 h of aeration requirement for fingerlings rearing at such high density. Further, no significant difference between survival levels in T-II and T-III groups suggested 8 h of aeration to be adequate. However, while species-wise performance showed 8–12 h night time aeration to be advantageous for catla and rohu, aeration for 4 h was adequate for fringe lipped carp and olive barb.     

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.     

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.     

Rapid and non-invasive measurements of fat and pigment concentrations in live and slaughtered Atlantic salmon (Salmo salar L.)

The aim of this study was to non-invasively determine fat and pigment concentrations in salmon muscle based on visible and near infrared (VIS/NIR) spectroscopy measurements of live/whole fish and fillets, and by means of digital photography (DP) of fillets. The fish used were two populations of farmed Atlantic salmon (Salmo salar L.) consisting of 46 salmon averaging 0.7 kg (range 0.17–1.7 kg, Group S) and 30 salmon averaging 2.3 kg (range 1.4–4.1 kg, Group L). Chemical analyses (fat and pigment content) and computerized tomography, CT (fat content) were used as reference methods. Group L was analysed in the live state (VIS/NIR), after gutting (VIS/NIR and CT), and as fillets (VIS/NIR and DP). Group S was analysed in the gutted state (VIS/NIR) and as fillets (VIS/NIR and DP). VIS spectroscopy predictions of pigment in whole salmon from Group S were obtained with a root mean square error of prediction (RMSEP) of 0.9 mg kg^− 1 astaxanthin, and a correlation between VIS spectroscopy predicted and chemically measured pigment of r = 0.85 (p < 0.0001). The fat concentration was determined by the NIR spectroscopy in live fish with RMSEP = 1.0 fat% unit, and a correlation with chemical reference values of r = 0.94 (p < 0.0001). Fat predictions from NIR spectroscopy correlated also well with predictions from CT analyses, r = 0.95 (p < 0.0001). VIS spectroscopy and DP were equally well suited to determine pigment concentrations in salmon fillets, with prediction errors of only 0.4 mg kg^− 1 astaxanthin, and a correlation with chemically determined pigment of r = 0.92 (p < 0.0001). The results obtained in the present study are the first to demonstrate successful non-invasive pigment predictions in whole salmon using VIS/NIR spectroscopy, and the possibility for simultaneous, rapid and non-destructive quantification of fat and pigment concentrations.     

Feeding and gut evacuation of cultured juvenile spiny lobsters, Jasus edwardsii

Low feed consumption has been suggested as a major impediment for the development of effective formulated diets for spiny lobsters. To seek an explanation for the low feed consumption, this study compared the feed consumption, appetite revival, foregut evacuation and fecal production of different sizes of spiny lobster Jasus edwardsii juveniles fed a fresh natural diet (i.e. mussel flesh) and a dry formulated diet. In addition, the effect of feeding frequency was determined by feeding juvenile lobsters the same ration of formulated diet at different time intervals. i.e., same ration delivered 3 week^− 1, 1 day^− 1, 2 day^− 1, 5 day^− 1 and 5 night^− 1. Lobster (10–15 g) growth and feed consumption (1.15% BW day^− 1) was maximized when receiving a single ration daily of the formulated diet. A slow appetite revival (AR > 18 h) on the formulated diet was consistent with the negative effect of increasing feeding frequency on growth and consumption. In addition, there appeared to be no major advantage in dry matter intake by providing the nutrient dense dry formulated diet to Jasus edwardsii. Lobsters fed fresh mussel flesh (79.8% moisture) consumed similar levels of dry matter as those lobsters fed the dry formulated feed (7.3% moisture). This appears to be due to high moisture gain and expansion of the dry feed in the lobster foregut. Foregut evacuation lasted 10 h for the two diets but a delay in initial foregut evacuation and processing of the formulated diet was evident, and may have negatively affected feed consumption, appetite revival and dry matter digestibility (61.2%) of the dry formulated diet compared to the mussel flesh diet (89.2%). Appetite revival on mussel flesh was almost complete by 12 h after a satiation ration and was governed primarily by the rate of foregut evacuation. Differences in the timing of foregut evacuation and fecal production between the two diets suggested that a greater proportion of the formulated diet entered the midgut directly.The results indicate that J. edwardsii cannot achieve high levels of feed consumption on formulated diets because gut throughput is reduced due to a small foregut capacity, expansion of the feed post-ingestion, lengthy foregut filling time (1–2 h) and clearance time (10 h), combined with slow gut throughput time (34–42 h) and appetite revival (> 18 h). A slow appetite revival and difficulties in processing and digestion of formulated diets appear as major issues to be resolved to improve the performance of formulated diets required for the commercial aquaculture of J. edwardsii and possibly other spiny lobsters.