Feed intake as explanation for density related growth differences of common sole Solea solea

Growth of common sole Solea solea is negatively correlated to density, which affects productivity in culture and hence commercial success. Studies of individual feed intake were performed to examine growth and population dynamics at different densities. Three initial stocking densities: 1.0, 2.1 and 3.9 kg m^?2 of individually tagged sole, referred to as low density (LD), medium density and high density HD), were examined during 145 days. Despite that tank productivity (g m^?2 day^?1), was highest for the HD group, the specific growth rate (SGR) decreased significantly with increase in stocking density. Individual size variation was similar between densities, indicating that growth was not associated with hierarchy and dominant behaviour. Individual data indicated that increased density reduced the growth potential of all individuals in a population. Individual feed intake was positively correlated to both fish size and individual SGR. Feed conversion ratio was likewise positively correlated to feed intake. The relative feed intake (g feed g fish^?1) was not correlated to fish size at any density tested, but was significantly highest for the LD population. This explains a substantial part of the better growth in the LD group supported by indications of better utilization of the ingested feed.     

Effect of stocking density on growth performance of juvenile sea cucumber Holothuria tubulosa (Gmelin, 1788)

Stock density is one among the most important factors in aquaculture that directly influences the growth of organisms; however, there is limited information about the effects of stocking density on growth performance of sea cucumber Holothuria tubulosa (Gmelin, 1788) that has a commercial potential and represents a new species for aquaculture. In this study, we investigated the effect of stocking densities on the growth performance of juvenile H. tubulosa (40.3 ± 3.34 g) in laboratory conditions. Stocking densities were selected as 6, 15 and 30 ind m^?2 with total biomass 253.3 ± 0.18, 601.2 ± 0.11 and 1201.4 ± 0.15 g m^?2 respectively. We monitored the growth by wet weights and calculated the growth performance through weight gain, growth rate, specific growth rate, relative weight gain, coefficients of variation and survival rate during 8 weeks of research period. We found that individual mean weight gain in 6 ind m^?2 group was approximately 29.53 g while it was 3.03 g and ?4.36 g for 15 ind and 30 ind m^?2 groups respectively. Results have shown that the specific growth rate tends to decrease as the number of individuals in unit area increases. The final mean weight, growth rate, specific growth rate, relative weight gain and coefficients of variation were significantly different among treatment groups. In conclusion, a density of 6 ind m^?2 is recommended for stocking juvenile H. tubulosa under rearing conditions. Stocking density of 15 ind m^?2 is not favourable for long term as the growth rate is negligible where 30 ind m^?2 should be avoided in tank‐based rearing units.     

In‐stream structure alters density‐dependent fish effects in stream ecosystems

The independent effects of in‐stream structure (ISS) and fish foraging on stream properties have been well documented, but few studies have explored the interactive effects of ISS and fishes on streams. Herein, we tested the independent and interactive effects of ISS and a generalist fish (Blacktail shiner, Cyprinella venusta) on suspended organic matter (SOM), benthic algae, invertebrate density and fish growth using experimental mesocosms. We found that Blacktail shiner foraging affected all of the ecosystem properties; however, in some cases, the fish effects differed between mesocosms with and without ISS. Specifically, mesocosms with ISS provided greater surface area for invertebrate colonisation and enhanced food resources for Blacktail shiner. As a result, benthic foraging by Blacktail shiner was reduced in these mesocosms. The reduced benthic foraging in turn enhanced benthic algae and benthic invertebrates via a bottom‐up, nutrient excretion pathway. The ISS‐dependent effects of fish on these stream properties, however, were only evident at low and intermediate fish densities (1 and 2 fish·m^?2 respectively). This was likely because at the highest fish density (4 fish·m^?2) intense fish foraging overrode any mediating effects of ISS. Furthermore, fish growth decreased with fish density because of intraspecific competition, but this negative effect on growth was reduced in mesocosms with ISS because of the increased forage base. However, the positive effect on fish growth was weak and only marginally significant. Our data suggest that fish‐mediated effects on streams are context dependent, changing with microhabitat availability (e.g. ISS) and density of the fish population.     

Aquaculture potential of the basket cockle (Clinocardium nuttallii). Part 1: effects of stocking density on first year grow‐out performance in intertidal and off‐bottom suspended culture

The basket cockle (Clinocardium nuttallii) is a candidate species for aquaculture in the northeast Pacific. The aim of the current research was to assess the feasibility of C. nuttallii grow‐out, with an emphasis on growth performance and qualities affecting product marketability. In this article, we investigated the combined effects of culture mode (intertidal and off‐bottom suspended culture) and initial stocking density (1500, 3000, 10 500 and 21 000 ind m^?2) on C. nuttallii survival and growth during the first year of grow‐out (May through October). In intertidal culture, cockles exhibited low survival and poor growth rates. In suspended culture, survival was consistently high (>96%) at all stocking densities tested; growth and condition parameters had the highest values at 1500 and 3000 ind m^?2. The edible portion (meat yield) exceeded 40% of the whole wet weight at all stocking densities, occurrences of fouled and deformed cockles were <1% and no commensal species were observed. Depending on the minimum harvestable size and stocking density chosen, harvestable proportions constituted from 1.1% to 15.2% by October of the first grow‐out year in the suspended system. The effects of stocking density and depth on second year grow‐out performance of C. nuttallii are reported in a companion paper (Dunham et al. in this issue).     

Maximum yield approximation and size distribution patterns of stocker size largemouth bass,Micropterus salmoides reared in a semi‐closed indoor system

The main objectives of this study were to approximate the maximum yield and evaluate size dispersion of stocker size largemouth bass, Micropterus salmoides reared in a semi‐closed recirculating system for 60 days. Fingerlings with an average body weight of 36.7 g were utilized for the study. An experimental system consisting of 18 square plastic tanks (165 L) equipped with a radial flow settler, a sump, a moving bed filter, a centrifugal pump, a rapid sand filter, a down‐flow oxygen saturator and a UV sterilizer was utilized for the trial. The system was operated semi‐closed, accounting for a daily exchange rate of 30–50% of total system water volume. Experimental stocking densities were 4.5, 9.1, 18.8, 36.5, 54.6 and 73 kg m^?3 with three replicates per treatment. At the end of the experimental trial, largemouth bass showed acceptable feed conversion (1.00–1.48), specific growth rate (1.16–1.45% day^?1) and survival rate (81.8–96.6%) in all treatments, displaying the highest performance at an initial stocking density range of 18–36 kg m^?3. Based on a piecewise regression model with breakpoint analysis, maximum yield of largemouth bass fingerlings should not exceed 70 kg m^?3. As stocking density increased, relatively more underweight fingerlings were produced with a higher uniformity of fatness.     

Effect of Intensification on Grow Out of the Amazon River Prawn, Macrobrachium amazonicum

The effects of intensification on growth, survival, productivity, population structure, and distribution of harvested biomass in individual size classes of Macrobrachium amazonicum in semi‐intensive culture were evaluated. Postlarvae (0.01 g) were stocked in 12 ponds at densities of 10, 20, 40, and 80/m² (three replicates per treatment) and raised for 5.5 mo. Average individual weight significantly decreased and productivity significantly increased as stocking density increased (P < 0.001), while survival was not affected (P > 0.05). Prawn mean weight at harvest ranged from 3.6 (80/m²) to 7.0 g (10/m²). Average survival ranged from 65.5% (40/m²) to 72.8% (20/m²), while productivity ranged from 508 (10/m²) to 2051 kg/ha (80/m²). Harvested biomass showed a clear bimodal distribution in individual size classes indicating the occurrence of heterogeneous growth, which may affect management and market strategies. Harvested biomass of prawns weighing more than 7 g (the best market size) increases for stocking densities up to 40/m² and stabilizes between 40 and 80/m². Growth reduction was associated with a decreasing frequency and average weight of green claw 1 and green claw 2 male morphotypes and adult females as density increased. Thus, the distribution of male morphotypes and sexually mature females are affected by density‐dependent factors. Results suggest that prawn density plays an important role on M. amazonicum grow‐out phase, as has been demonstrated for other species of the genus Macrobrachium. M. amazonicum tolerates grow‐out intensification and may be raised in both semi‐intensive and intensive systems stocked at very high densities yielding high productivity.     

Effects of stocking density on intermediate culture of the razor clam Ensis arcuatus (Pharidae: Bivalvia)

Commercial production of most bivalve species involves a phase of intermediate cultivation during which juveniles are grown under protected conditions until they can be transferred to the final grow‐out location. Consequently, the aim of this study was investigating the effect of density on growth and survival in the intermediate culture of the razor clam Ensis arcuatus in raft. Two series of experiments were performed, using in the first experiment two holding systems: 5‐L plastic bottles and PVC cylinders, both perforated, covered with a 1 mm mesh net to prevent razor clam escape and a 10‐cm layer of coarse grained sand (300–1200 μm grain diameter). In this trial, two stocking densities were tested: 0.15 and 0.30 kg m^?2. In the second one‐two densities were essayed (0.62 and 1.24 kg m^?2) in the PCV cylinders. In the first experiment after 27 of trial higher growth in cylinders at low density was observed. At the end of this trial all juveniles died in the 5‐L plastic bottles and higher growth and survival were recorded in the cylinders at low density. In the second experiment, significant differences in growth and survival were found on day 70, with the best results at low density. Five‐L plastic bottles must be rejected as holding system for the intermediate culture of E. arcuatus and the PVC cylinders at low densities could be a good alternative. At the end of the experiment razor clams reached the adequate size for their transfer into the grow‐out system.     

Heritability and genotype by environment interactions for growth and survival in Litopenaeus vannamei at low and high densities

Genetic parameters and genotype by rearing density interactions for growth traits and survival were investigated in Litopenaeus vannamei. A total of 3626 shrimps from 40 families in two densities (low density, 80 shrimps m^?2; high density, 160 shrimps m^?2) were measured for four growth traits, body length, body weight, cephalothorax length and abdominal segment length. Variance components and genetic parameters for growth and survival were estimated using a two‐trait animal model or a threshold (probit) sire and dam model. The common environment effect was excluded because it could not be partitioned effectively, likely because of high heritability. The heritability for growth traits varied from 0.21 to 0.44, indicating a moderate level. For survival, the back‐transformed heritability () was 0.36 ± 0.06 and 0.22 ± 0.04 for the low and high densities respectively. There were no significant differences in heritability for growth traits and survival between the two densities (P > 0.05). High genetic correlations (0.94–0.98) between the two densities for growth traits indicated a low genotype by density interaction and ranking effect across the environments, which suggested that these traits were controlled mostly by the same genes over the two densities. Therefore, selection in a low‐density environment should produce desired correlated responses for growth at a high density. Genetic correlation (0.77 ± 0.09) between the two densities for survival was moderate and significant, which indicated that the genotype by density interaction effect was moderate and low for survival under the two densities. Our results provide crucial information for use in L. vannamei breeding programmes in China.     

Enhanced growth and immuno‐physiological response of Genetically Improved Farmed Tilapia in indoor biofloc units at different stocking densities

An experimental trial was conducted for 90 days to evaluate the growth performance, immunophysiological response of GIFT strain of Tilapia in biofloc‐based rearing system and to assess the relative percentage survival in 3 days after challenging with the virulent strain of Aeromonas hydrophila. Fingerlings with an average body weight 0.98 ± 0.06 g were stocked in triplicate at different stocking densities of 200 (SD1), 250 (SD2), 300 (SD3) and 350 (SD4) m^?3 in biofloc‐based treatments and 150 (C) m^?3 in control (clear water). Biofloc‐based units (SD1 and SD2) obtained significantly better (P < 0.05) growth performances at the end of the experimental period. Mean body weight of fish in biofloc‐based units showed a decreasing trend with increase in stocking density with 100% survival in all units including control. The stress parameters were significantly lower in biofloc‐based rearing units especially in treatments SD1 and SD2 as compared to the control. The fish from the biofloc‐based units (SD1 and SD2) possessed significantly (P < 0.05) higher immune status as compared to control and other biofloc treatments in terms of respiratory burst, serum lysozyme and myeloperoxidase activity. Relative survival percentages were significantly better in biofloc treatments with highest in SD1 and SD2 (83.33%) after challenge study. GIFT strain of Tilapia at higher stocking densities 200–250 nos m^?3 can be taken as optimum stocking density whereas higher stocking densities up to 350 nos m^?3 can be reared in the biofloc systems without compromising the growth and immunity.     

Influences of population density,temperature and latitude on the growth of invasive topmouth gudgeon Pseudorasbora parva

Plasticity in life‐history traits provides advantages for introduced fish in overcoming demographic bottlenecks that would otherwise inhibit establishment. Here, the influence of population density, temperature and latitude was tested on the growth increments and growth rates of invasive populations of topmouth gudgeon Pseudorasbora parva, a small Asian cyprinid fish that is invasive across Europe. Aquaria experiments tested the roles of fish number and temperature on growth increments under a fixed food supply, pond experiments tested the role of density on growth increments, and a field study completed in England and Wales tested the influence of density and latitude on growth rates. In aquaria experiments, whilst growth increments were higher at 21 and 23 °C than at 19 and 25 °C, fish number had a greater influence on growth than temperature. Higher growth increments were produced at lower densities. In experimental ponds, growth increments were significantly higher in ponds with low densities of P. parva compared with those at elevated densities. In the field study comprising 10 wild populations across a latitudinal gradient of 4.0°N, a difference in mean air temperatures of approximately 3 °C, and estimated densities between 0.5 and 65.0 m^?2, population density was the only significant predictor of growth rates. Whilst populations at very low densities comprised of significantly faster growing individuals, there were no significant differences when densities were between 15 and 65 m^?2. Thus, invasive P. parva populations have considerable growth plasticity, especially at low densities, with this likely to be important in their ability to colonise new environments.     

Influence of stocking density on the behaviour of juvenile Litopenaeus vannamei (Boone, 1931)

Applied ethology can help to improve Litopenaeus vannamei aquaculture. Our purpose was to demonstrate an influence of stocking density on behaviour. The shrimp were first distributed in aquaria and observed via an ad libitum observational method to construct an ethogram of social and feeding behavioural categories. The resulting ethogram consisted of retreat, cannibalism, getting to the feeding tray, occupying the feeding tray and getting feed. We then kept shrimp in aquaria at densities of 50, 75 and 100 animals m^?2 and observed them via a behavioural sampling method using our ethogram as well as focal animal sampling of behaviours derived from the literature. These literature‐derived behaviours consisted of inactivity, feeding, crawling, exploration, burying, swimming and cleaning. We found that stocking density affects the behaviour of the shrimp. Optimal searching and feeding and a low frequency of crawling and swimming occurred at a density of 50 animals m^?2, indicating a higher potential for growth and welfare at this density.     

Co‐culture of sea cucumber Holothuria scabra and red seaweed Kappaphycus striatum

Commercially valuable sea cucumbers are potential co‐culture species in tropical lagoon environments, where they may be integrated into established aquaculture areas used for seaweed farming. In the current study, wild‐caught juvenile sea cucumbers, Holothuria scabra, and red seaweed Kappaphycus striatum were co‐cultured on Zanzibar, United Republic of Tanzania. Sea cucumbers (97 g ± 31 SD, n = 52) were cultured in mesh enclosures at initial cage stocking densities of 124 ± 21 SD and 218 ± 16 SD g m^?2 under seaweed culture lines. Over 83 days, individual growth rate (1.6 g d^?1 ± 0.2 SD) of sea cucumbers at low stocking density was significantly higher (χ² = 8.292, d.f. = 1, P = 0.004) than at high‐stocking density (0.9 g d^?1 ± 0.1 SD). Seaweed individual growth rates [6.27 (±0.3 SE) g d^?1] were highest in co‐culture with sea cucumber at low density but did not differ significantly from high sea cucumber density or seaweed monoculture treatments (χ² = 3.0885, d.f. = 2, P = 0.2135). Seaweed growth varied significantly (χ² = 35.6, d.f. = 2, P < 0.0001) with sampling period, with the final sampling period resulting in the highest growth rate. Growth performance for seaweed and sea cucumbers (χ² = 3.089, d.f. = 2, P = 0.21 and χ² = 0.08, d.f. = 1, P = 0.777 respectively), did not differ significantly between monoculture and co‐culture treatments, yet growth in co‐culture was comparable with that reported for existing commercial monoculture. Results indicate H. scabra is a highly viable candidate species for lagoon co‐culture with seaweed. Co‐culture offers a more efficient use of limited coastal space over monoculture and is recommended as a potential coastal livelihood option for lagoon farmers in tropical regions.     

Effect of Stocking Density on Growth,Physiological Responses,and Body Composition of Juvenile Blunt Snout Bream,Megalobrama amblycephala

The impact of stocking density on growth performance, physiological indicators, and body composition of juvenile blunt snout bream in recirculating aquaculture system was investigated in this study. Juvenile blunt snout bream were raised at stocking densities of 75, 150, 225, 300, and 450 fish/m³ for 12 wk with three replicate tanks at each density. All treatment tanks were supplied with water from the same recirculating system to ensure uniformity of water quality across groups. This study has shown that higher stocking densities had a negative effect on individual growth performance. Final body mass, specific growth rate (SGR), and weight gain decreased significantly as stocking density increased. Individual body mass as well as body length were more uniform in fish stocked at densities of 75 and 150 fish/m³ than in other groups. Stocking densities of 225 and 300 fish/m³ resulted in significant increases in serum total protein, triglyceride, lactate, and cholesterol levels, whereas blood glucose concentrations decreased significantly. In addition, decreased body lipid content and increased body moisture content were observed at stocking densities of 300 and 450 fish/m³. Overall, a density of 150 fish/m³ resulted in higher SGR and more uniform size among juvenile blunt snout bream.     

The Effects of Biomass Density on Size Variability and Growth Performance of Juvenile Largemouth Bass,Micropterus salmoides,in a Semi‐closed Recirculating System

This study evaluated the effects of biomass density on size variability and growth performance of feed‐trained largemouth bass, Micropterus salmoides, fingerlings in a semi‐closed recirculating system for 60 d. Average individual body weight and length of fingerlings were 9.04 g and 9.07 cm, respectively. Experimental biomass densities were set at 15, 20, 25, 30, 35, and 40 kg/m³. Water temperature was adjusted to approximately 25 C and dissolved oxygen concentration was maintained above saturation. Fish were fed a formulated diet (42% protein) distributed by automatic feeders for 12 h daily. During the experiment, fingerlings actively fed and presented high survival rates (96.8–95.0%) at all densities. Growth performance of fingerlings was not affected by the biomass densities tested in this study (P < 0.05). The ranges of size distributions were similar among treatments, but more fingerlings were near the average size at lower biomass densities. Based on the results of this study, largemouth bass fingerlings were tolerant of high biomass density and a gross yield of 100–125 kg/m³ may be viable for largemouth bass reared in a semi‐closed recirculating system up to 30 g in weight.     

Competitive release modifies the impacts of hydrologic alteration for a partially migratory stream predator

Understanding ecological effects of altered stream flows is an essential objective. In a comparative field study of juvenile steelhead trout (Oncorhynchus mykiss) that compared natural‐ and reduced‐flow sites, we used mark–recapture modelling and information theory to quantify spatially and temporally explicit patterns of density, specific growth rate, survival and outmigration; and test predictions for biotic and abiotic drivers. Densities were lower in water withdrawal treatments, resulting in lower intraspecific competition and, higher specific growth rate and survival. We observed yearly differences in density and intraspecific competition, with a negative relationship between density and specific growth rate over a wide range of densities, but reductions in survival only at the highest densities. Moreover, individual variability within sites was important. At high density (sites and years), survival related negatively to body size. In contrast, when overall density was lower, specific growth rate was negatively related to body size. Lastly, individuals were more likely to outmigrate when they had larger body size, lower survival or reared in habitats with reduced flows, and these patterns appeared mediated by the intensity of intraspecific competition. Our results underscore the harsh bioenergetic conditions induced by higher temperatures and densities during summer baseflow (relative to other seasons), particularly for larger fish demanding more resources, and suggest a density‐dependent mechanism for why this period is important for regulating salmonid populations. We found that a complex combination of natural (e.g., density) and anthropogenic (e.g., withdrawal) factors affected juvenile salmon populations and life history expression in the face of altered flows.     

Determining an effective density regime for rearing juvenile Austropotamobius pallipes in a small‐scale closed system hatchery

With recent advances in aquaculture techniques, captive‐breeding of the endangered white‐clawed crayfish Austropotamobius pallipes for restocking is becoming a widespread conservation method. Establishing optimal stocking densities for aquaculture is essential in maximizing productivity, and increases the likelihood of crayfish survival when released. A 240‐day experiment took place using 2‐month‐old juvenile, captive‐born, A. pallipes, within a small‐scale, closed‐circuit hatchery to investigate survival, growth and aggression at three treatment densities, low (100/m²), medium (200/m²) and high (300/m²). Crayfish were counted and measured every 60 days between August 2015 and April 2016. Mean survival rates were high across all three densities (87.7% ± 2.8%). Carapace length was significantly longer at low density than at medium and high densities. While growth rate was not significantly different between treatments, it was significantly higher in the first 2 months, across all three treatments (47.1% ± 6.6%) than in subsequent periods (14.1% ± 5.8%). Size variation within groups increased with density, suggesting that social dominance hierarchies are established with increasing stocking density: dominant individuals are larger and competitively exclude smaller individuals from food resources. Males were significantly larger than females from 6 months of age, (when they could be reliably sexed), in all three treatments. The larger male size suggests that sexual dimorphism begins prior to sexual maturity, with males growing faster and being more dominant and aggressive than females. In conclusion, young‐of‐the‐year A. pallipes can be reared at high densities without compromising survival; however, the optimal stocking density that maximizes growth and health is 100/m².     

Effects of density on growth and survival of juvenile Red Swamp Crayfish, Procambarus clarkii (Girard), reared under laboratory conditions

The aim of this study was to quantify the importance of population density on the growth and survival of juvenile red swamp crayfish, Procambarus clarkii (Girard), and to understand the effects of density on both the period between moults and the increment per moult at high densities without food limitation. A laboratory experiment was performed to determine growth and survival of juvenile crayfish at five densities (20, 40, 60, 80 and 100 crayfish m^?2). Density clearly affected crayfish growth. The impact of density on final weight was higher than on total length increase, growth rate and final length (FL) (by decreasing order of effect). When comparing minimum and maximum densities, we observed that FL suffered a 34% reduction. Number of moults, mean intermoult period (IP) and survival were not significantly affected by density. Our results indicated that the IP and the percentage of increment per moult are affected by the size of crayfish before moult and we provide equations for these relations. Our findings are relevant both for crayfish aquaculture management and for the management of wild or harvested rice‐field crayfish populations.     

Optimization of the stocking parameters for mud spiny lobster Panulirus polyphagus (Herbst, 1793) capture‐based aquaculture in tropical open sea floating net cages

Mud spiny lobsters, Panulirus polyphagus (Herbst, 1793), were reared at four different stocking sizes and stocking densities in open sea cages to evaluate their effects on growth performance. To evaluate the effect of stocking size on the growth performance, the lobsters were segregated into four different treatment groups according to size and were stocked at a density of 300 animals per cage. To evaluate the effect of stocking density on the growth performance, lobsters of 81–100 g were stocked in four different stocking densities, i.e. 16/m², 24/m², 32/m² and 40/m². The results showed that the growth rate of (60–80 g) size group, was significantly higher compared to the size groups, i.e. 101–120 g and 121–140 g comprising of larger individuals. The final body weight, though significantly higher in 81–100 g as compared to 60–80 g, the growth performance (i.e. weight gain percentage (WG %) and specific growth rate (SGR)) were not significantly different. The density‐dependent influence on growth performance was evident in this study. The WG % and SGR during 90 days’ culture period was significantly higher in 24/m² compared to other groups. This study provides crucial information about the appropriate stocking density and stocking size of lobsters at the field level, which would help to promote sustainable lobster cage farming by maximizing the production potential of the system.     

Nutritional status of a nereidid polychaete cultured in sand filters of mariculture wastewater

This study examined the nutritional composition of the intertidal marine polychaete Perinereis helleri (Nereididae) when artificially cultured in sand filters treating mariculture wastewater. Moisture levels in harvested P. helleri ranged from 758 to 855 g kg^?1, and ash, from 23 to 61 g kg^?1 wet matter (WM). Stocking density and graded size after harvest significantly affected their composition. Higher total lipid contents were found in large (>0.6 g) P. helleri (16–19 g kg^?1 WM) and those grown at the lowest density (1000 m^?2: 18 g kg^?1 WM) than in small (≤0.6 g) ones (14 g kg^?1 WM) and those grown at the highest densities (4000–6000 m^?2: 13–16 g kg^?1 WM). Several fatty acids within a very broad profile (some 30 identified) reflected this pattern, yet their ARA/EPA/DHA ratios were relatively unaffected. Feeding the polychaete‐assisted sand filters (PASF) with fish meal to increase worm biomass productivity significantly increased their DHA content. Other components (e.g. protein, phospholipids, cholesterol, carbohydrate, amino acids, nitrogen, minerals and bromophenols) and nutritional factors (e.g. maturity, feeding seaweed and endemic shrimp viral content) were also investigated. Results suggest that PASF‐produced P. helleri have a well‐balanced nutritional profile for penaeid shrimp and fish broodstock.     

Effects of photoperiod and stocking density on survival,growth and physiological responses of narrow clawed crayfish (Astacus leptodactylus)

Photoperiod and stocking density are critical factors influencing the performance of decapod crustaceans in culture, however, their influence on growth; survival and biochemical physiology of crayfish broodstock have rarely been considered. Analysis of biochemical physiology in crayfish broodstock during the non‐breeding season provides information on the energy storage requirements of broodstock for increased survival and reproductive output. Growth rate, moulting frequency, survival and biochemical physiology were measured in Astacus leptodactylus broodstock that were cultured at three different photoperiods (18L:6D; 12L:12D; and 6L:18D) and three stocking densities (10, 20 and 40 individuals m^?2) during non‐breeding season. Survival of crayfish was highest at 18L:6D photophase and 10 m^?2 (100%) than other treatments. Survival in the high stocking density was high when combined with 18L:6D photophase, but weight gain (WG) and specific growth rate (SGR) were higher at shorter photophase and lower stocking density. Longer photophase (18L:6D) increased stress responses, characterized by increased haemolymph lactate and glucose levels. Stocking density did not affect proximate composition of crayfish; however, individuals cultured at 18L:6D photophase had higher lipid content than other photoperiod treatments. The study demonstrated that culturing A. leptodactylus at 18L:6D photophase and 10 m^?2 is critical for increased survival of broodstock.