Grow‐out performance of Kuria labeo,Labeo gonius (Hamilton), with major carps in carp polyculture system

A year‐long grow‐out carp polyculture trial was conducted in nine earthen ponds to study the growth performance of Kuria labeo (Labeo gonius) with the different major carps such as catla (Catla catla), silver carp (Hypophthalmichthys molitrix), rohu (Labeo rohita) and mrigal (Cirrhinus mrigala). Suitable water quality parameters were maintained in ponds through intermittent liming, manuring and fertilization. Three different species combinations of carps were evaluated using silver carp and catla as the common species and varying other carp components as rohu–Kuria labeo, mrigal–Kuria labeo and rohu–mrigal in the three treatments. The ponds were stocked at a combined density of 7500 fingerlings ha^?1. Silver carp and catla showed similar growth performances in all the three combinations, suggesting that other carps in the combination do not have any differential influence on their growth. Kuria labeo was compatible with rohu, while competition was observed with mrigal. Although growth performance of Kuria labeo was inferior to that of mrigal, better compatibility of Kuria labeo with rohu helped this combination to yield a biomass equivalent to the mrigal–rohu combination, suggesting feasibility to use Kuria labeo as an alternative species to mrigal in the major carp polyculture system without compromising the total biomass yield.     

Establishing a benchmarking for fish farming – Profitability,productivity and energy efficiency of German,Danish and Turkish rainbow trout grow‐out systems

The promotion of Blue Growth in aquaculture requires an understanding of the economic drivers influencing the sector at farm level, but the collection of reliable and comparable data at this level is time‐consuming and expensive. This study suggests an alternative strategy for qualitative sampling of freshwater trout farms in Germany, Denmark and Turkey, using a combination of existing data, group discussions and interviews with trout farmers, consultants and researchers. Nine ‘typical’ trout farming models are described, focusing on profitability, productivity and energy efficiency and allowing in‐depth comparative economic analyses of different production systems at farm level, across regions. Our results show that the majority of the farms investigated have been profitable. Turkish farms benefit from competitive advantages due to low wages, low capital investment and favourable climate conditions. Large German farms profit from local market prices and advanced farm management. Danish farms using recirculating techniques remain competitive thanks to enhanced productivity and economy of scale. However, small traditional farms in Germany and Denmark may struggle to stay competitive in the long term. Organic farms in both countries face challenges of high feed costs and comparatively low productivity with mixed success. Using edible protein energy return on investment (epEROI) as an indicator of ecological sustainability, all surveyed farms compared very favourably with the terrestrial systems of animal meat production were investigated so far.     

Trial grow‐out culture of sea cucumber Holothuria scabra in sea cages and pens

Field trials were conducted to determine the effects of size, grow‐out period and site on the growth and survival of Holothuria scabra. Juveniles were reared in sea cages in two sites for 2 months during two different times of the year. Juveniles from Experiment 1 were subsequently grown in sea pens for 8 months in one site. The significantly lower survival particularly of the small‐sized group (<0.1 g) in Pilar is likely due to reduced water and sediment quality because of proximity to fish‐farming activities. The importance of grow‐out period was evident in the significant differences in weight increments in all size groups and biomass in the small‐sized group (P < 0.10) in Lucero during Experiment 2 when water temperature range and incidence of rainfall were higher. The decrease in the average weight of adults during the second half of the grow‐out period may be due to the interplay of the reduction in salinity, onset of sexual maturity and biomass exceeding carrying capacity in the pens. The estimated biomass threshold in the sea cages and pens in Lucero were 300 g m^?2 and 380 g m^?2 respectively. Implications of the results on the viability of small‐scale pen grow‐out culture are discussed.     

Aquaculture potential of the basket cockle (Clinocardium nuttallii). Part 2: effects of stocking density and depth on second year grow‐out performance of three size cohorts in intertidal and off‐bottom suspended culture

We investigated the effects of culture mode (intertidal and off‐bottom suspended culture) and initial stocking density (5%, 10%, 35% and 70% bottom cover) on survival, growth and condition indices of three size cohorts (16, 22 and 32 mm initial shell length) of the basket cockle, Clinocardium nuttallii, during a second year of grow‐out. In addition, we evaluated the effects of depth (2, 4 and 6 m) in suspended culture. All size cohorts demonstrated significantly higher growth rates, soft‐tissue biomass and condition indices in the off‐bottom suspended system compared to the intertidal one. In suspended culture, however, C. nuttallii exhibited sub‐optimal survival, shell deformities and heavy fouling. For all size cohorts, stocking density had a significant effect on most growth and condition parameters, except meat yield indices, in both culture modes. An initial maximum stocking density of 10% cover is recommended for all size cohorts. Culture depth did not have a consistent statistically significant effect on any of the growth or condition parameters. Depending on the grow‐out scenario, stocking density and harvestable size chosen, the cumulative harvestable proportion after the second year of grow‐out constituted 15.5–63.1% of the seed planted. Our results could be used to develop and improve culture techniques for C. nuttallii and other cockle species.     

Efficacy of Netminder® silicone release coating for biofouling reduction in bay scallop grow‐out and comparative effects on scallop survival,growth and reproduction

Netminder^®, a water‐based silicone barrier release coating, was highly effective in reducing biofouling of lantern nets during grow‐out/overwintering of bay scallops, Argopecten irradians irradians, in a large‐scale restoration programme in New York, USA. Compared with untreated nets, scallops held in Netminder^®‐coated nets experienced reduced survival after 8 months, probably due to higher loads of epibionts on their shells. However, this was countered by higher reproductive and overall condition of scallops in treated vs. untreated nets; there were no consistent differences in shell growth in different net treatments. Although further testing is recommended under a wider range of conditions, we conclude that for the purposes of our scallop restoration work, coating nets with Netminder^® would eliminate the need for a gear change in spring, thus reducing labour costs; the coating process should be refined so that Velcro closures of nets do not become sealed shut.     

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).     

Effects of soybean meal and high‐protein sunflower meal on growth performance,feed utilization,gut health and gene expression in Arctic charr (Salvelinus alpinus) at the grow‐out stage

The effects of two plant ingredients (solvent‐extracted soybean meal [SBM] and high‐protein sunflower meal [HPSFM]) and three inclusion levels (0 percent, practical diet containing 25 percent fish meal; 12.5 percent; and 25 percent) of these ingredients were investigated on the growth, feed utilization, gut histology and gene expression in the distal intestine of Arctic charr Salvelinus alpinus (average initial weight, 330.1 ± 8.9 g per fish). Feeding experimental diets for 12 weeks resulted in no difference between HPSFM diets in body weight gain (BWG), thermal‐unit growth coefficient (TGC), feed efficiency (FE), feed intake (FI) or pro‐inflammatory mRNA expression (PIE) with increasing dietary inclusion and between SBM FE, FI and PIE. Differences in quadratic contrasts were observed for nitrogen deposition rate (NDR) and nitrogen retention efficiency (NRE) (p < .05), whereby HPSFM diets elicited the strongest positive response. SBM resulted in linear reduction in BWG, TGC and distal intestine simple fold length and width measurements (p < .05) with stepwise increases in dietary inclusion, whereas dietary HPSFM had no effect. Histological observations of individual villi indicated several symptoms of non‐infectious subacute gastrointestinal enteritis in tanks fed SBM, many of which were not present in tanks fed HPSFM. The dietary HPSFM seems to be more adequate to replace fishmeal in Arctic charr diet than SBM, when fed at a level of up to 25 percent at the grow‐out stage.     

Shell shape and meat condition in selectively bred Sydney rock oysters,Saccostrea glomerata (Gould, 1850): The influence of grow‐out methods

The Australian edible oyster industry has been severely impacted by disease and declining yields since the 1970s. Selective breeding of Saccostrea glomerata is one measure addressing these problems by producing fast‐growing, disease‐resistant oysters. Farmers report that selected oysters have different growth characteristics than their wild counterparts using conventional grow‐out methods. This study investigated how different grow‐out methods influence commercially valuable oyster characteristics including shell length, shape, surface growth deformities and meat condition. In June 2015, selectively bred S. glomerata spat were deployed in two estuaries (Hawkesbury River and Georges River) in NSW, Australia, using three grow‐out methods (fixed trays, Stanway cylinders and floating baskets). In November 2015, oysters were transferred among grow‐out methods to test for the effects of changing grow‐out methods on oyster growth patterns. Oysters transferred from baskets to cylinders and from trays to cylinders had, on average, deeper and wider shells, a higher meat condition and fewer shell surface deformities than oysters in other grow‐out method combinations. However, these oysters were smaller than oysters not grown in cylinders. While there were some differences in growth patterns between the estuaries, overall it was the grow‐out methods that most influenced oyster characteristics. This was attributed to differences in the amount and magnitude of movement oysters experienced in the grow‐out methods, as recorded by motion sensors. This study demonstrates how grow‐out methods can be managed to achieve desired growth trajectories and therefore improve marketability among selective bred S. glomerata.     

Nano zinc vis‐à‐vis inorganic Zinc as feed additives: Effects on growth,activity of hepatic enzymes and non‐specific immunity in rohu,Labeo rohita (Hamilton) fingerlings

The effects of dietary administration of inorganic zinc (zinc sulphate, ZnSO₄) and nano zinc (zinc oxide nanoparticles, ZnO‐NP) were evaluated in rohu, Labeo rohita fingerlings. Fish were fed with a basal diet (Control) supplemented with ZnSO₄ (T1, T2 and T3) and ZnO‐NP (T4, T5 and T6) at 10, 20 and 30 mg/kg, respectively, for a duration of 45 days. The results revealed that fish fed diet containing 20 mg ZnO‐NP per kg (T5) had the highest weight gain and specific growth rate (SGR, % per day), which was significantly different (p < .05) from the other experimental diets. Significantly (p < .05), higher activities of the digestive and metabolic enzymes were recorded in the fish fed ZnO‐NP containing diets as compared to the diets containing inorganic Zn or control diet. The maximum serum glucose and protein levels were noted in fish reared on diet T5. Both SGOT and SGPT activities were significantly increased in fish fed Zn‐supplemented diets (T1 to T6), as compared to the control group. Similarly, innate immune parameters were improved with feeding Zn incorporated diets. The highest phagocytic (40.74 ± 0.65%) and respiratory burst (0.33 ± 0.001, OD 630nm) activities were recorded in the fish fed diet containing ZnO‐NPs at 20 mg/kg (T5). The maximum superoxide production and serum peroxidase activity were detected in the fish fed T5 and T6 diets. Overall, results indicated that short‐duration feeding (≤45 days) of dietary ZnO‐NP (20 mg/kg) improved growth, enzyme activity, serum biochemical parameters and immune function in rohu fingerlings.