Initial Stocking Density Research Articles

Does Stocking Density Affect Growth Performance and Hematological Parameters of Juvenile Olive Flounder Paralichthys olivaceus in a Recirculating Aquaculture System?

Olive flounder Paralichthys olivaceus is a representative culture species in South Korea. Recirculating aquaculture systems (RASs) have received increased attention because they can provide sustainable and environmentally friendly productivity. However, to maintain economic sustainability, the system generally requires high productivity, achieved through a high stocking density, which compromises animal welfare. The reduction in growth based on the stocking density may be due to the social hierarchy resulting from the growth suppression of subordinate individuals. Species, size, culture systems, and other management regimes can affect the social hierarchy. Therefore, a more practical approach must be taken to adjust the stocking density for a particular fish species and fish size in a specific culture system. This study investigated the effect of stocking density on juvenile olive flounder in an RAS. Juvenile olive flounder (61.0 ± 0.3 g) were initially stocked at 3.29, 4.84, 7.14, and 8.56 kg/m2 (T1, T2, T3, and T4, respectively). After 8 weeks, growth performance, in terms of feed conversion, specific growth rate, and daily feed intake rate, was measured. In addition, the blood levels of insulin-like growth factor (IGF-1), growth hormone, glucose, glutamic oxaloacetic transaminase, and glutamic pyruvic transaminase and the whole-body composition were evaluated as stress indicators. Growth performance increased as stocking density increased, but fish at the highest stocking density showed signs of growth reduction toward the end of the experiment. In addition, as stocking density increased, IGF-1 decreased, and cortisol increased. The whole-body protein level was significantly lower in T4 compared with the other treatments. Olive flounder seemed to tolerate a stocking density up to 20.16 kg/m2. Based on the growth performance, hematological response, and whole-body composition results in the present study, a final stocking density of 20 kg/m2 (from the initial stocking density of 4.84-7.14 kg/m2) may be desirable for juvenile olive flounder in an RAS for fish weighing ~60-180 g.

Response of germination and seedling growth of Jute plant (Corchorus olitorius L.) on three different substrates in the tilapia aquaponic system

The merging of fish farming and crop husbandry in a mutual system forms aquaponics. In this system, the nature of the planting substrate plays a significant role in the germination, establishment, and growth of the plant. In the current experiment, the germination and growth of the Jute plant ( Corchorus olitorius L . ) in an aquaponics system with tilapia fish was investigated using three different substrate types: gravel, rice husk, and palm kernel shell. Five hundred-liter plastic tanks containing tilapia fingerlings at initial stocking densities of 250 fish m −3 were used. One gram of Jute seed was sown in a 1 m 2 planting trough, which contained the three substrates separately in triplicates. The troughs were flooded with water from fish holdings by an aquarium pump. The germination percentage of the jute plant on gravel substrate (84%) and rice husk (72%) was significantly higher (P < 0.05) compared to the palm kernel shell (55%). A lower velocity of germination was also recorded in the palm kernel substrate. The rates of growth in height (centimeters per day) of jute plant and fresh shoot biomass yield were significantly lower on palm kernel substrate (P < 0.05). Growth and yield parameters of jute showed comparatively higher agronomic efficiency of gravel and rice husk substrates compared to palm kernel substrates in this research. The results indicated that substrate nature significantly affects the germination and productivity of C. olitorius in aquaponic systems and that rice husk has the potential to serve as a planting substrate in aquaponics. • Response of germination and seedling growth of Jute plant ( Corchorus olitorius L.) on three different substrates in the tilapia aquaponic system. • Influence of substrate types on the germination and productivity of C. olitorius in aquaponic systems. • Potentials of rice husks as planting substrate for Jute in the aquaponic system.

Earthworm stocking density regulates microbial community structure and fatty acid profiles during vermicomposting of lignocellulosic waste: Unraveling the microbe-metal and mineralization-humification interactions

Earthworm-induced microbial enrichment is the key to success in vermitechnology, yet the influence of initial earthworm stocking density on microbial community profiles in vermibeds is unknown. Therefore, vermicomposting of lignocellulosic feedstock was performed with different stocking densities of two earthworms (Eisenia fetida and Eudrilus eugeniae) compared with composting. Eventually, earthworm growth, microbial (activity and community profiles), and physicochemical dynamics were assessed. The earthworm population significantly increased under low stocking, while denser stocking (15/kg) was stressful. The XRD-based crystallinity assessment revealed that comminuting efficiency of Eisenia and Eudrilus was prudent at 7 and 10 worm/kg stockings, respectively. Moreover, the 5 and 7 worm/kg stockings effectively mobilized microbial activity, promoting NPK-mineralization and C-humification balance. Correlation statistics indicated that earthworm stocking density-driven microbial community shift and fatty acid profiles strongly influenced metal removal in vermibeds. Hence, the findings implied that 5–7 worm/kg stockings of earthworms produced high-quality sanitized vermicompost.

Effect of Agricultural By-Products as a Carbon Source in a Biofloc-Based System on Growth Performance, Digestive Enzyme Activities, Hepatopancreas Histology, and Gut Bacterial Load of Litopenaeus vannamei Post Larvae

The present study evaluated the influence of different commercial agricultural by-products as a carbon source in a bifloc-based (BFT) culture system on growth performance, whole-body proximate composition, digestive enzyme activities, gut microbial abundance, and hepatopancreas histology of Pacific whiteleg shrimp, Litopenaeus vannamei post larvae (Pls). Three groups were designed, the first group was the control group, where the shrimp was reared in clear water (without carbon source addition and water exchange rate of 100% two times a week) and fed with a commercial diet, in the second and third groups shrimp were reared in BFT systems using two different carbon sources, sugarcane bagasse (SB) and rice bran (RB) without additional feeding or water exchange. The initial stocking density was 16 Pls/liter with an average individual shrimp weight of 0.01 ± 0.002 g and age (PL20). The experiment lasted 90 days. The water quality parameters were maintained at optimum levels during the experiment. The final body weight and specific growth rate of shrimp were significantly (p ≤ 0.01) higher in the control group than those reared in both SB and RB-based BFT. Meanwhile, the survival rate was significantly (p &lt; 0.05) higher in BFT groups than in the control. The protease activity in shrimp stomach did not differ significantly. Meanwhile, protease, lipase, and amylase in the intestine showed a significant increase (p &lt; 0.01) in BFT groups than those obtained in the control group. The total heterotrophic bacteria were significantly (p &lt; 0.05) higher in BFT groups. Furthermore, the hepatopancreas histological status of shrimp reared in the SB-based BFT group showed an increase in the hepatopancreas tubules in the distal and B-cell zones (blister-like cells) by 16.83 and 34.89%, respectively, compared to the control. This study revealed that BFT could be used as a natural feed without artificial diets, which influenced the gut microbiota of shrimp, increased digestive enzyme activities, as well as improved the histological structure of the hepatopancreas of shrimp. However, the success of this conditions under high stocking density still needs more investigation.

Development of larviculture protocols for the long-spined sea urchin (Diadema antillarum) and enhanced performance with diets containing the cryptophyte Rhodomonas lens

Slow or nonexistent natural recovery of the Caribbean long-spined sea urchin (Diadema antillarum) following a mass mortality event in 1983–1984 has prompted interest in hatchery-origin production and restocking to aid coral-reef restoration. A critical first step is the ability to propagate D. antillarum from gametes, at scale. However, a unique larval biology and difficult and lengthy culture period of ~ 40 days has resulted in inconsistent success over the past 20-plus years. The purpose of this study was to develop protocols for rearing D. antillarum within a novel 1800-L recirculating aquaculture system capable of scaled production. Five separate experiments investigated larval development in response to diet quantity, diet composition, and initial stocking density within 40-L replicate culture tanks. The initial experiment was used to develop a microalgae reference diet consisting of Tisochrysis lutea and Chaetoceros sp. and revealed similar growth and survival between high quantity (40.0 × 103 cells mL−1) and low quantity (10.0 × 103 cells mL−1) treatments at 21 days post-fertilization (DPF). Experiments 2–4 examined diet quality by comparing carbon-equivalent microalgae compositions. Mixed diets containing Rhodomonas lens outperformed the reference diet in multiple experiments and a tripartite diet containing all three species resulted in significantly higher survival at 42 DPF. The highest growth overall occurred from a monoalgal R. lens diet, which indicated that this species is critically important. Further observations of density-dependent growth dynamics revealed that initial stocking densities > 1 larvae mL−1 significantly reduced growth over 28 DPF. Data generated were used to establish fundamental larviculture protocols that have since led to the production of over 1000 juveniles.

Pengaruh Bobot Bibit Awal yang Berbeda terhadap Laju Pertumbuhan Rumput Laut Kappaphycus alvarezii dengan Metode Lepas Dasar

There are several factors that will inhibit the growth of seaweed when the cultivation process is the initial stocking density in the off-bottom method. This study aims to determine the effect of different awa seed weights on the growth rate of K. alvarezii seaweed which will provide information regarding the optimal initial weight. This research was carried out in April-May 2021 for 42 days with an acclimatization period of 3 days and preparation of containers for 7 days. Berakit Village, Teluk Sebong District, Bintan Regency, Riau Islands Province. The method used is an experimental method with a completely randomized design (CRD) with 3 treatments with 3 replications. Where the weight of the seeds of treatment A: 50 g, B 100 g, C 150 g, The results of the analysis of the highest absolute growth were obtained in seaweed with initial seed weight of 50 treatments. g with the highest average value of 207.75±9.02b, followed by treatment of 150 g with an average value of 166.78±6.96a and the lowest treatment of 100 g with an average value of 157.04±1.48a. Meanwhile, the highest daily specific growth rate was focused on the 50 g treatment with an average value of 4.95±0.22% b followed by the 150 g treatment with an average value of 3.97±0.17% and the lowest treatment was in the 100 g treatment with an average value of 3.74± 0.04%. Treatment of different initial seedling weight with off-base method gave a significant effect on Absolute Growth (PM) and Daily Specific Growth Rate (LPS) during maintenance.

Effect of newly isolated high antioxidant diatom on the reproduction and stress tolerance of the marine copepod, Acartia erythraea under crowding stress

This study evaluated the effect of antioxidants on a tropical coastal copepod, Acartia erythraea, under crowding stress by using the high-antioxidant, diatom algal strain Thalassiosira weissflogii TRG10-P105 (TW P105) as feed. This newly isolated diatom strain has higher antioxidants than the generic strain Thalassiosira weissflogii (generic TW), which is used as a common feed in copepod culture. Incubation experiments were carried out under various crowding levels (100, 250, 500 and 1000 ind/L). Acartia erythraea, on Day 1, showed comparable and highest egg production and hatching success rate (ca. 68%) at Day 1 with the lowest initial stocking density (100 inds/L) regardless of prey type, indicating both algal strains have similar nutritional potential for egg production under less stressful conditions. However, declining reproduction with increasing initial stocking density through the experimental period was more obvious in copepods with generic TW than in those with TW P105. At initial stocking density of 500–100 inds/L, no egg hatching was observed with generic TW during the latter half of the experiments, while those with TW P105 showed a constantly higher hatching success (30%–80%) during the same period. Overall, A. erythaea fed on TW P105 had much better stress tolerance at high initial stocking density (~1000 inds/L) with 2–3 times higher cumulative number of egg and nauplii compared with generic TW. This result implies that the high-antioxidant diatom algal diet is more effective in ameliorating the adverse effects caused by high density cultivation of copepods than a diet of cogeneric strains.

Growth and population modelling based on density of the Pacific white shrimp intensively cultured in freshwater

Mathematical representation of the growth of organisms in aquaculture systems is a key factor to perform optimal production. Here, we analysed five growth sigmoidal models based on density of previous and current models described in literature (Gompertz, Bertalanffy, Potential and Pütter). These models were fitted to data of Pacific white shrimp cultured in freshwater, with 90, 130, 180, 230, 280 and 330 shrimp/m2 as initial stocking density of culture. Goodness of fit and statistic validation of the density-dependent model modified from Gompertz proved to display the growth curve that best-described data of shrimp grown between 90 and 180 densities, whereas the growth model modified from Potential proved to best describe higher stocking densities (230–330). The population dynamics was also modelled using a density-dependent function. The implications of modelling and their importance in the management of fisheries are discussed.

Effect of water recirculation rate and initial stocking densities on competent larvae and survival of the Pacific oyster Crassostrea gigas in a recirculation aquaculture system

Effect of water recirculation rate and initial stocking densities on competent larvae and survival of the Pacific oyster Crassostrea gigas in a recirculation aquaculture system

Effects of Stocking Density on Stress, Hematological Responses, and Growth of Black Rockfish Sebastes schlegelii.

The objective of the current study was to evaluate the effect of stocking density on juvenile Black Rockfish Sebastes schlegelii (average weight = 12 g) in terms of stress, hematological responses, and growth performance during a 4-month growth trial in a flow-through system. The initial stocking densities were 1.3 kg/m3 (low), 1.8 kg/m3 (medium), and 2.3 kg/m3 (high), and the final densities were 4.9 kg/m3 (low), 5.6 kg/m3 (medium), and 6.3 kg/m3 (high). At the end of the trial, the high stocking density significantly affected growth characteristics, levels of growth hormone and insulin-like growth factor 1, and hematological indices (hematocrit, red blood cell count, and hemoglobin level) compared to the medium and low stocking densities. The plasma cortisol and immunoglobulin-M levels were significantly higher at the high density than at the other two densities. Taken together, while the low and medium stocking densities (final densities of up to 5.6 kg/m3 ) did not affect stress and hematological indices or growth, the high stocking density (final density of 6.3 kg/m3 ) significantly impacted those variables, which suggests an allostatic load at that density. Thus, the use of a final stocking density less than 6.3 kg/m3 should be considered to avoid compromising the stress and health condition and growth of Black Rockfish at this size and temperature range.

Evaluation of two spawning induction methods and effect of stocking density and microalgal diet composition on larval growth and survival of Pacific clam, Asaphis violascens (Forsskål, 1775)

AbstractPacific clam, Asaphis violascens is a benthic species present in the Indo‐pacific region. It is very much appreciated as food by the local community and its population is diminishing due to overfishing. The aim of this research is to establish suitable rearing conditions for its spawning and larviculture. Two different spawning induction methods were used, emersion and thermal shock. Two stocking densities of larvae were tested (10 and 20 larvae/mL) and three different microalgae diets, one consisting of Tisochrysis lutea as a single species diet and the other two with Ti. lutea combined with Nannochloropsis oculata and Tetraselmis suecica. Emersion of clams was established as a successful spawning induction method. Larval development of A. violascens is similar to other tropical bivalves, having a 10‐day planktonic period at 28°C. An initial stocking density of 10 larvae/mL showed significantly higher (p &lt; .05) survival rate. No significant differences (p &gt; .05) in growth and survival were found between the diets, proving that the use of Ti. lutea alone or mixed is suitable for their nutrition. The results presented could contribute to the implementation of restorative aquaculture farms in the region, helping to mitigate food security issues in the communities and collaborating with the establishment of healthier coastal ecosystems.

Reducing cannibalism among larval striped bass Morone saxatilis: Effects of Artemia ration size and stocking density

Two trials on striped bass larvae, both 2 × 2 factorial design and 16 days duration starting at 12 days post-hatch (dph; 3 mg body weight, BW), compared the effect of stocking density (both trials 3 vs. 15 larvae/L; rearing volume 15 L) and daily fixed ration of stage II enriched Artemia (Trial 1: 1000 vs. 250; Trial 2: 250 vs. 50 Artemia per larva per day; Art/l/d) based on initial stocking density. Losses of larvae were categorized as either retrieved mortalities or ‘missing’ due to cannibalism. In Trial 1, ration (1000 vs. 250 Art/l/d) had a highly significant (p < 0.001) effect on both overall losses (4 vs. 22%) and final mean wet BW (55 vs. 18 mg), whereas stocking density had a minor influence on losses (p = 0.038), and no effect on final BW (p = 0.700). Losses due to cannibalism in Trial 1 were very low (< 3%). In Trial 2, by contrast, cannibal losses were up to 52%, and overall losses up to 80% primarily due to the low ration of 50 Art/l/d. Overall losses in Trial 2 were strongly dependent on ration (p = 0.028), but independent of stocking density (p = 0.426). Some cannibals grew very fast, their final BW > 10-fold greater than conspecifics. In a small production trial, larvae stocked at 15/L were offered a daily ration that increased progressively from 250 Art/l/d at 14 dph to 1200 Art/l/d at 29 dph. Survival was 95% due to negligible cannibalism. Overall, the study presents a protocol for the indoor intensive production of striped bass through the larval stage with minimal losses to cannibalism.

Valorization Use of Amphipod Meal, Gammarus pulex, as a Fishmeal Substitute on Growth Performance, Feed Utilization, Histological and Histometric Indices of the Gut, and Economic Revenue of Grey Mullet

The future of aquaculture development is directed toward high intensification to overcome the decline in natural fishing and to provide enough protein for the increasing world population. The spread of aquaculture production and intensification requires the search for high-quality, new efficient feed ingredients with low cost and sustainable importance. Therefore, the current study aimed to detect the effects of partial or total replacement of fishmeal with amphipod meal, Gammarus pulex, on growth performance, survival percent, feed utilization, histological alteration of intestine and liver, and economic yield of grey mullet, Mugil cephalus, fry. Five diets were formulated to contain 100% fishmeal (FM), or FM replaced with 25%, 50%, 75%, or 100% amphipod meal (APM) (D0, D25, D50, D75, and D100, respectively). A total of 300 grey mullet fry (0.097 ± 0.001 g), were divided into five groups (three replicates each) at an initial stocking density of 20 fry per aquaria (100 L). The aquarium’s water is renewed at a rate of 30% daily. During a 60-day experimental period, the feeding rate was 20% of body weight, which was introduced as five meals per day. Fish fed D50 achieved the highest significant values of final weight (1.80 g), weight gain (1.70 g), survival (86.67%), final length (4.47 cm), and length gain (2.06 cm). In addition, the feed utilization of diets containing increasing substitution levels of FM showed that the highest protein intake (0.82 g ish−1), protein efficiency ratio (0.83), protein productive value (30.65%), and the lowest significant feed conversion ratio (1.21) were recorded with D50. The dose-response study revealed that the best substitution levels could range between 50% and 75%. Histological observations confirmed that the highest number of goblet cells and intestinal villi were recorded in the group fed D50. No pathological effect was observed in the liver at all substitution levels. In terms of economic efficiency, the best economic conversion ratio was recorded in the group fed D50. This study confirmed that 50% partial substitution of FM with APM is the ideal replacement level for grey mullet fry. In addition, the use of a new renewable alternative, such as APM to substitute FM, could relieve the pressure on the capture of wild fish and reduce the environmental impact of inland aquaculture.

Effect of stocking density and algal concentration on production parameters of calanoid copepod Acartia bilobata

The present study investigated the effect of initial adult stocking densities and algal concentrations on production parameters of calanoid copepod, Acartia bilobata. Experiments were in triplicate with seven initial stocking densities (125, 250, 500, 1000, 2000, 4000, and 8000 adult copepods L−1) fed at three different concentrations (0.5, 1 and 5 ×105 cells mL−1) of Isochrysis galbana. Various production parameters; egg and nauplii production, egg hatching success, adult survival, and sex ratio were estimated. Individual egg production (IEP) increased from day one to five in all the groups irrespective of stocking densities and algal concentrations. IEP decreased significantly (p < 0.05) on day 1 from 9.61 ± 0.79–0.17 ± 0.05 eggs female−1day−1, and on day 5 from 13.44 ± 2.94–2.99 ± 0.58 eggs female−1day−1 with increase in stocking density from 125 to 8000 adult copepods L−1 respectively; however, an increase was noted as algal concentration increased. Total accumulated egg production increased upto the density of 1000 adults L−1, with 33945.02 ± 1556.43 eggs L−1 at highest algal concentration, and thereafter declined at higher densities. Synergistic effect of stocking density and algal concentration significantly impacted 16 and 24 h hatching success. Copepod adult survival decreased significantly from 71% to 78% (125 adult copepods L−1) to 2–10% (8000 adult copepods L−1) with increase in stocking density. It is concluded that moderate stocking density of 1000 adults L−1 with highest algal concentration (5 × 105 cells mL−1) is optimum for higher reproductive performance (egg production and hatching success) of A. bilobata. Present study provides baseline information for A. bilobata commercial mass production for use in hatcheries.

Simplified Hatchery Protocols for Culture of Orange-Spotted Spinefoot Siganus guttatus (Bloch, 1787) in Palawan, Philippines

Three hatchery experiments for orange-spotted spinefoot, Siganus guttatus (Bloch, 1787), were carried out in Puerto Princesa City, Palawan, Philippines using larvae and fingerlings produced through induced spawning. The first experiment (E1) involving larvae raised in six 5,000-L concrete tanks until 39 days post-hatch (dph) comparing two stocking densities (T1: 3; and T2: 5 larva.L-1), obtained survival rates (SR) of 6.00 and 7.85 %. The second experiment (E2) monitored the growth and survival of 47 dph juveniles for 3 weeks, raised in 25-L plastic basins, fed with a commercial diet at three stocking densities with five replications. The initial stocking densities (6, 12, 18 ind.L-1) were reduced during the second (4, 8, 12 ind.L-1) and third (2, 4, 6 ind.L-1) week, respectively. The weekly SR for all treatments ranged between 99.2 and 100 %. Weekly final total lengths (TL) were not significantly different except during the second week. The third experiment (E3) evaluated the effects of two types of commercial feeds (T1: grouper feed; T2: milkfish feed) on the growth and survival of 47 dph juveniles in plastic basins for 3 weeks, at similar densities reduced on a weekly basis. The SR (96.2 to 99.9 %) were not significantly different, but the TL of fish in T1 (4.39 cm) were significantly bigger than in T2 (3.52 cm). While there is a need to improve the low and irregular survival of S. guttatus larvae for cost-effective large-scale production, we recommend using small basins in the intensive rearing of juveniles.

Experimental testing of density- and season-dependent growth in vegetative Fucus aquaculture and modelling of growth over one year for different cultivation scenarios

In the Kiel Fjord, western Baltic Sea, an experimental culture of Fucus vesiculosus and Fucus serratus has been established in order to develop a sustainable method for biomass production of these species. The cultivation method includes the unattached rearing of fronds in drifting baskets and their vegetative reproduction by cutting of small vegetative apices. In this study, we performed culture experiments to measure growth rates with this method at different initial stocking densities (1–5 kg m−2) and during different seasons of the year. Using the results, we modelled growth over 1 year for different cultivation scenarios (different initial stocking densities (1–4.75 kg m−2) and harvest densities (1.25–5 kg m−2)) in order to identify optimal scenarios and estimate annual yields and the number of necessary harvests in these scenarios. Fucus vesiculosus showed a parabolic yield–density relationship with decreasing yields at high initial stocking densities (> 2.5 kg m−2). In contrast, F. serratus showed an asymptotic yield–density relationship with rather constant yields at high initial stocking densities. Both species showed a typical seasonal growth pattern with low growth rates during winter and high growth rates during summer; however, F. serratus seemed to be growth limited during summer which was not observed for F. vesiculosus. The modelling results reflected the results of the Density experiment: for F. vesiculosus, optimal cultivation scenarios were found for intermediate cultivation densities (initial stocking densities, 1.75–2.25 kg m−2; harvest densities, 3–4 kg m−2); for F. serratus, optimal cultivation scenarios included higher densities (initial stocking densities, 2.5–4 kg m−2; harvest density, 5 kg m−2). The model scenarios predicted maximal annual yields of 6.65–6.76 kg m−2 for F. vesiculosus and 6.88–6.99 kg m−2 for F. serratus. For both species, the number of harvests necessary to achieve these yields varied depending on the cultivation scenario from 2 to 6. Scenarios with only 1 harvest per year yielded slightly lower annual yields. We conclude that the modelling results offer a valid and helpful orientation for future efforts to produce Fucus species in commercial culture.

Effects of Stocking Density on Growth Performance and Stress Responses of Bester and Bester ♀ × Beluga ♂ Juveniles in Recirculating Aquaculture Systems.

Simple SummaryThe disappearance of many wild sturgeon populations from natural waters and the high demand for sturgeon products (meat and caviar) have led to increased aquacultural production of sturgeons. The development of recirculating aquaculture systems requires the optimization of rearing technologies so that high stocking densities have a minimal impact on fish health. Due to the ease with which sturgeons hybridize, the optimization of sturgeon aquaculture technologies involves the identification of hybrid lines with high technological performance and high stress resistance. One of the best known hybrids is that between the beluga and the sterlet (bester). The present study aims to evaluate the hybrid obtained by crossing the bester (female) with the beluga (male) as a new candidate for the recirculating aquaculture systems. The results show better performance and better density adaptation of the bester × beluga hybrid compared with the bester hybrid. However, at higher stocking densities, a negative impact on growth performance and physiological response was observed.The study aimed to compare the growth performance and physiological responses of bester (B) and backcrossed bester ♀ × beluga ♂ (BB) in response to crowding stress under different stocking densities, as well as to establish a threshold stocking density for rearing BB in a recirculating aquaculture system (RAS) without welfare impairment. For this purpose, in the first trial (T1), B (181.15 ± 21.21 g) and BB fingerlings (181.98 ± 28.65 g) were reared in two stocking densities of 2 kg/m2 and 4 kg/m2 in fiberglass tanks (1 m3) for 6 weeks. In a parallel trial (T2), the BB hybrids (335.24 ± 39.30 g) were kept in four initial stocking densities, ranging from 5 kg/m2 to 12 kg/m2. The results of T1 revealed better growth indices (i.e., final mean weight, weight gain, specific growth rate) at lower stocking densities for both hybrids; however, in terms of growth performance, the BB hybrid showed better results when compared with the B hybrid. BB hybrids registered significantly (p < 0.05) lower serum cortisol and MDA and higher lysozyme than B hybrids, showing higher tolerance to crowding stress. Nevertheless, at higher densities, selected serum parameters (i.e., hematological indices, cortisol, glucose, protein, malondialdehyde, lysozyme) and growth performance indices used to evaluate the hybrids indicate that high stocking density could affect the growth and welfare of BB hybrids, and that the selected serum parameters could be used as good indicators for chronic stress caused by overcrowding conditions.

Stocking density alters growth performance, serum biochemistry, digestive enzymes, immune response, and muscle quality of largemouth bass (Micropterus salmoides) in in-pond raceway system.

The effects of stocking density on growth performance, serum biochemistry, digestive enzymes, immune response, and muscle quality of largemouth bass (Micropterus salmoides) reared in nine in-pond raceway systems (IPRS, 22.0 m × 5.0 m × 2.0 m) were studied. M. salmoides with initial an body weight of 8.25 ± 0.51 g and body length of 6.99 ± 0.44 cm were reared at an initial stocking density of 90.91 ind./m3 (low stocking density, LSD), 113.63 ind./m3 (middle stocking density, MSD), and 136.36 ind./m3 (high stocking density, HSD) with triplication. After 300 days of culture, MSD recorded the highest final body weight, weight gain, specific growth rate, and yield, but the food conversion ratio in MSD was the lowest. The viscerosomatic index in LSD was significantly higher than other groups. The fish serum reared at HSD showed significantly lower total protein, higher total cholesterol, triglyceride, total bilirubin, glucose content, alanine transaminase, and aspartate transaminase activity. Significantly lower intestinal amylase, lipase, trypsin activities, hepatic superoxide dismutase (SOD) and catalase (CAT) activities, and higher malondialdehyde content were detected in HSD compared to others. The content of crude lipid, saturated fatty acid decreased, and total essential amino acid, delicious amino acid, and polyunsaturated fatty acid increased in muscle with stocking density increase. No significant difference was observed in muscle texture. Profitability analysis indicated the benefit-to-cost ratio varied between 1.10 and 1.68, of which MSD was significantly higher than others. The optimal stocking density for M. salmoides should be 113.63 ind./m3 in an IPRS farm.

Efecto de la densidad sobre el crecimiento en fase de engorde del mejillón, &lt;i&gt;Mytilus edulis platensis&lt;/i&gt;, en el golfo San Jorge, Patagonia argentina

The aim of this study was to determine the stock density effect on size and biomass on mussel Mytilus edulis platensis, at growth up phase ropes. These ropes were made using three initial stocking densities: 200, 300 and 400 mussels m-1 and hung on in a longline at Belvedere site on San Jorge gulf, Argentina. Stock density showed no influence on individual mussel biomass. Higher growth length was obtained at higher densities. According to these results, when the mussels are in the fattening or thinning out phase, the optimum stocking density would be 300 to 400 mussels m-1.

Comparison and optimization of a novel larval rearing method for bighead carp Hypophthalmichthys nobilis

Bighead carp Hypophthalmichthys nobilis is a species that is widely cultured throughout Asia, currently ranking 5th in overall global fish production. Despite the prevalence of this species culture it is considered invasive in North America and a threat to local fish communities. Investigations into the early life environmental requirements and optimization of intensive larval rearing have been limited. The present study attempts to establish most desired larval rearing conditions of bighead carp by investigating a novel static rearing method utilizing continuous light, salinity (2 parts per thousand; ppt), algal turbidity, and continuous food availability as compared to traditional recirculating culture system methods. Increased levels of salinity (3 and 5 ppt) were also examined in the novel rearing environment. A 2x2x3 full factorial ANOVA design was implemented to compare the main effects of larval rearing system, feeding regime, and stocking density (12.5, 25, and 50 fish L−1) and the interactions between the main effects on survival, biomass, length, weight, proportion of large fish (measure of heterogeneity), and specific growth rate over twenty days of feeding. A desirability function was then constructed to maximize survival (%), biomass (g L−1) and proportion of large fish to optimize larval rearing for diet nutritional requirement studies. Mortalities recorded in the experiment primarily occurred within the first ten days of feeding and leveled off during the second ten days of feeding. The desirability function identified the novel static rearing method, at high initial stocking density (50 fish L−1), and feeding with Artemia nauplii from inception as having the maximum desirability (0.733) for the selected variables. The predictions for biomass, survival and proportion of large fish from the desirability function were 2.38 g L−1 (95% CI, 2.14–2.62), 70.3% (95% CI, 60.1–80.6), and 0.768 (95% CI, 0.696–0.841) respectively. Elevated salinity, 3 and 5 ppt, was found to increase survival (51.3 ± 3.5 and 64.3 ± 10.1%, respectively) and proportion of large fish (0.76 ± 0.08 and 0.82 ± 0.02, respectively) i.e. decreased heterogeneity, as compared to 2 ppt (33 ± 3% and 0.63 ± 0.03) in the novel static rearing environment. This indicates that current results may further be improved if bighead carp are reared at higher salinities (3–5 ppt). The optimization methodology which was utilized in the current study could potentially be applied to any larval rearing program to select for treatments which meet specific desired outcomes.