Comparison between traditional methods and artificial neural networks for ammonia concentration forecasting in an eel (Anguilla anguilla L.) intensive rearing system

One of the main problems in the management of fishfarms with water recirculating system is the forecasting and control of ammonia concentration in order to minimise the fish stress status. This paper examines methodologies of prediction in a real-time environment for an eel intensive rearing system. Approaches based on linear multiple regression, univariate time series models (exponential smoothing and autoregressive integrated moving average (ARIMA) models) and computational neural networks (ANNs) are developed to predict the daily average ammonia concentration in rearing tanks with water recirculating. The models are established using actual data from an eel fishfarm in southern Spain. The input variables used in the models (multiple regression, Holt smoothing model, ARIMA models and ANN models) are the ammonia concentration of previous days. In ANN models, the training method used is a standard back-propagation variation known as extended-delta-bar-delta (EDBD). Different neural architectures, whose learning is carried out by crossvalidation and controlling several threshold determination coefficients, are compared. Globally, the nonlinear ANN model approach is shown to provide a better prediction of daily average ammonia concentration than linear multiple regression and univariate time series analysis when the correlation between data series is low and when the models were obligated to predict in a situation for which specifically had not been calibrated. The best results were obtained by 5:10s:15s:1l ANN model in the pre-growth series.     

Use of GIS and machine learning to predict disease in shrimp farmed on the east coast of the Mekong Delta,Vietnam

Diseases in shrimp farms in the Mekong Delta of Vietnam cause significant crop losses and are therefore of great concern to producers. Once a pond becomes infected, it is difficult to prevent spread of the disease to nearby shrimp farming areas. Thus, predicting the occurrence of disease is an essential part of reducing the risk for shrimp farmers. In this study, we applied an integrated geographic information system and machine learning system to predict three serious diseases of shrimp, namely, acute hepatopancreatic necrosis, white spot syndrome disease, and Enterocytozoon hepatopenaei infection, based on data collected from shrimp farms in the Tra Vinh, Bac Lieu, Soc Trang, and Ca Mau provinces of Vietnam. We first constructed a map showing the distribution of these diseases using the locations of affected farms, and then we conducted spatial analysis to acquire the geographical features of the affected locations. This latter information was combined with environmental factors and clinical signs to form the set of independent variables affecting the outbreak of diseases. The neural network model outperformed the logistic regression, random forest, and gradient boosting methods in terms of predicting infection to estimate the probability of disease occurrence in farmed areas. Acute hepatopancreatic necrosis disease infected farms downstream of the Co Chien and Hau Rivers of Tra Vinh and west of Ca Mau. Enterocytozoon hepatopenaei infection is distributed in Soc Trang Province, while white spot syndrome virus has spread to the coastal districts of Soc Trang and Bac Lieu Provinces, where it is highly associated to water from a complex canal system.

     

COVID-19 impacts on the Bangladesh shrimp industry: A sequential survey-based case study from southwestern Bangladesh

Shrimp farming is fundamental to the national economy of Bangladesh, particularly through earning foreign currency. The nationwide lockdown and international cargo restriction jeopardized the sector and breaking its marketing chain. Assessing the degree of farming socio-economic peril from COVID-19 and suggesting early coping strategies and long-term mitigation measures are pressing to build resilience for this food production sector. To collect survey data, two key-informant face-to-face surveys with 51 shrimp farmers and 62 consumers in southwest Bangladesh were accomplished. As national lockdowns restricted access to export markets and movements within the country, farm incomes decreased against rising production costs. To compensate, farmers reduced their workforce (29.4%), but even with the sale of co-cultured finfish still suffered from large drops in revenue (42.8% average profit reduction). Furthermore, we present evidence that shrimp farmers should consider diversification of aquaculture product type as co-culture of additional shrimp species was a poor mitigation strategy against large market price fluctuations. Product price reductions were passed on to the consumer, who enjoyed falling product prices including more expensive shrimp products, but the markup for nearly all aquaculture products increased. The current jeopardy and consequences of shrimp farming future are discussed, including coping strategies to help policymakers in building resilience against future uncertainties.

     

Biosecurity and Genetic Improvement of Penaeid Shrimp: Applications to the Marine Ornamental Industry

The marine ornamental industry relies almost exclusively on wild-caught fish, invertebrates, and live rock to meet the market demands of aquarium hobbyists. For the industry to expand, appropriate technologies are needed to mitigate disease problems and reduce the dependence on wild stocks. Biosecurity protocols and techniques for genetic improvement have recently been applied to the culture of penaeid shrimp for human consumption, and these approaches may be applicable to an emerging marine ornamental industry. Biosecure production systems for penaeid shrimp are being developed in response to disease problems and growing concerns about environmental pollution from pond effluent. Biosecure systems rely on minimal water exchange and provide shrimp farmers with an opportunity to move production away from the coastline. In addition to the development of biosecure production systems, researchers at the Oceanic Institute have established a selective breeding program for the Pacific white shrimp, Litopenaeus vannamei. To date, significant improvements in shrimp growth and disease resistance have been made through selective breeding. It is likely that advances in biosecure technologies and genetic improvement will be applicable to the culture of marine ornamental shellfish and finfish and will contribute to an economically viable and environmentally sustainable industry.     

舟山地区大棚凡纳滨对虾生长缓慢病因的调查分析

2013年以来,浙江省舟山地区大棚养殖的凡纳滨对虾(Penaeus vannamei)普遍出现生长缓慢、养殖成功率低的现象。为了查明该原因,本研究采用分子生物学和组织病理学等方法对引起对虾生长缓慢的病因开展了调查分析。结果显示,采集的270份病虾样本中,对虾肝肠胞虫(Enterocytozoon hepatopenaei,EHP)PCR阳性检出率高达85.19%,传染性皮下及造血器官坏死病毒(infectious hypodermal and hematopoietic necrosis virus,IHHNV)检出率为0;所有采集的病虾样本中也未分离到常见的致病菌;54份正常的对虾样本中EHP和IHHNV均未检出。将病虾PCR扩增产物进行序列测定和比对分析,结果获得的序列片段与Gen Bank中已有EHP相关序列相似性高达99.55%;病虾的肝胰腺组织病理切片观察显示,在虾肝胰腺组织中可观察到处于各个生长发育阶段的EHP。通过上述研究,初步认为EHP是引起舟山地区大棚养殖对虾生长缓慢的一个重要病原。     

Biosecure Shrimp Feeds and Feeding Practices: Guidelines for Future Development

For the purposes of this paper, biosecure shrimp feeds and on‐farm feeding strategies refer to the “feed, whether live, fresh, or formulated, and the management of the feed on the farm, should not be an entry point of potential pathogens to the shrimp and/or to the culture system.” The paper reviews the different feeds commonly used for the production of farmed shrimp and discusses their potential risks from a disease perspective, including the use of live hatchery and nursery feeds, the use of live and/or fresh food organisms for the production of broodstock, and the use of dry formulated shrimp feeds for shrimp growout operations. In addition, the paper discusses the critical role played by feed‐processing techniques for the pasteurization and destruction of pathogens within shrimp feeds and the need for nutritionists to formulate feeds for optimal nutrition and health, and not just for optimal growth. The importance of the development and implementation of good on‐farm feed management practices by farmers is discussed, including the prohibition of the top‐dressing of pelleted feeds on farm by farmers with unapproved feed additives such as antibiotics. Finally, the paper discusses the responsibilities of farmers, feed manufacturers, and traders regarding the development and use of recommended biosecure shrimp feeds and feeding practices.     

Explanation of Size Diversity Among Artemia Cohorts: A Model of Food Uptake Kinetics

Models describing the food uptake kinetics of a growing Artemia culture and the hatching rate of Artemia cysts are combined to yield equations capable of predicting the effects of variable algal cell concentration upon the growth rates of brine shrimp cohorts. The model illustrates that the feeding ability of the brine shrimp can be viewed as one becoming increasingly more efficient as the animals mature. This increasing efficiency in a population of variable age animals (from a single hatch) results in accelerated growth of first hatched animals relative to later hatched animals, especially at algal cell concentrations below certain threshold values. Growth rates of variable age groups of brine shrimp are mathematically manipulated to predict variable size brine shrimp at low algal cell concentration and uniformly sized brine shrimp at high algal cell concentration. This predicted result is confirmed with data from Artemia growth trials at high and low algal cell concentrations. It is suggested that similar variations in population attributes of other species may be explained as an animal-food interaction in which minor initial variations in individual animal maturity (weight, size, etc.) are magnified as a consequence of continuous competition for a common pool of food.     

Better management practices and their outcomes in shrimp farming: evidence from small-scale shrimp farmers in Southern Vietnam

Despite the growth of aquaculture exports from developing countries to developed countries in recent years, a high percentage of these products are rejected at developed countries’ ports because of non-compliance with international standards. This paper presents a case study of the shrimp aquaculture sector in Vietnam to examine the factors behind the persistence of such port rejections. In particular, we focus on why the so-called better management practices (BMPs) are not appropriately adopted by many farmers and examine whether the number and types of information sources matter in farmers’ decisions on BMP adoption and whether BMP adoption actually leads to better performances. On the basis of our estimation using primary data collected in Southern Vietnam, we find that information sources and training experiences indeed matter in the adoption of a higher number of BMPs and that BMP adoption indeed reduces the possibility of disease outbreaks. These results prove the effectiveness of BMPs and suggest the importance of disseminating knowledge regarding them to farmers through experts.     

Growth and reproductive performance of broodstock shrimp reared in a biosecure recirculating aquaculture system versus a flow-through pond

Over the past decade, viral pathogens have caused mass mortalities of farmed shrimp throughout the major shrimp farming regions of the world. In addition, the global shrimp farming industry has been criticized for negatively impacting coastal environments. These issues have raised concerns about the sustainability of traditional shrimp farming practices, and have prompted farmers and researchers to develop biosecure technologies that promote a sustainable industry. Current technologies include the use of specific pathogen free (SPF) shrimp that are grown to market size in recirculating systems that rely on pathogen exclusion. Inherent in this approach is the need to produce SPF broodstock under biosecure conditions. However, there is a paucity of information on broodstock growth and reproductive performance when they are reared in recirculating systems. The present investigation compares shrimp growth and reproductive performance in two trials where shrimp were cultured from market size (20 g) to broodstock size (40–60 g) in a recirculating aquaculture system (RAS) versus a flow-through earthen pond (EP). In trial 1, mean growth rates of males and females in the RAS were 0.83 and 1.33 g/week, respectively. In the EP, males and females grew 1.07 and 1.48 g/week, respectively. In trial 2, mean growth rates of males and females in the RAS were 0.90 and 1.53 g/week, respectively, whereas in the EP, males and females grew and 1.24 and 1.78 g/week. Slower growth rates in the RAS may be attributed to the lack of natural productivity, which provides supplemental nutrition to the shrimp. In addition to growth rates, reproductive performance of broodstock reared in the RAS was compared with historical reproductive performance of broodstock reared in the EP. Data on spawning success and production of viable nauplii revealed no significant differences (P>0.05) between broodstock shrimp reared in these two systems. These results indicate that broodstock shrimp can be cultured in a biosecure RAS while maintaining good growth and high survival. In addition, reproductive performance of broodstock shrimp reared in a RAS is not compromised when compared with broodstock shrimp reared in a conventional, flow-through pond.     

A future vision for disease control in shrimp aquaculture

Aquaculture is the fastest‐growing animal production sector, and shrimp production already exceeds that of the capture fishery. Viruses and bacteria account for the majority of disease losses for shrimp farmers. Viral pandemics in the mid 1990s and, more recently, a bacterial pandemic from 2009 to 2015 have led to the conclusion that future, sustainable shrimp aquaculture will depend on the development of more efficient, biosecure production facilities that cultivate specific pathogen‐free (SPF) shrimp, genetically improved for growth and disease tolerance or resistance. Major requirements for development, maintenance, and use of SPF stocks in aquaculture are effective pathogen surveillance and disease prevention methods. When protective measures fail and diseases occur in production ponds, there are currently only a few approved and practical therapeutic methods available for use with bacterial pathogens and none so far for viral pathogens. To improve existing methods of prevention and therapy and to develop new ones, research is being carried out on the nature of shrimp–pathogen interactions. Promising results have been obtained at the laboratory level for possible applications involving the use of immunostimulants for “immune priming” or “trained immunity” of RNA interference and of endogenous viral elements. Some of these promising new directions are discussed.     

Acute and Chronic Effects of Nitrite on White Shrimp, Litopenaeus vannamei, Cultured in Low-Salinity Brackish Water

The marine white shrimp Litopenaeus vannamei is widely cultured. Recently, farmers have begun to culture this shrimp in low-salinity brackish water (< 6 g/L). The intensification of shrimp culture often results in occurrences of elevated nitrite concentration during the growing season. Nitrite is toxic to shrimp and exposure to high concentrations may cause retarded growth and mortalities. The current study was aimed at investigating the acute and chronic toxicity of nitrite to L. vannamei grown in low-salinity (2 g/L) brackish water. Studies of the 96-h EC50 and LC50 values of nitrite were performed to determine the acute toxicity, and an aquarium growth study (2 d post exposure to elevated nitrite concentrations) was conducted to evaluate the chronic effects of nitrite on shrimp production. The 96-h EC50 and LC50 values for juvenile L. vannamei grown in water of 2 g/L salinity was about 9 mg/L NO₂-N, suggesting a safe concentration for shrimp production in ponds to be less than 0.45 mgIL NO₂-N. Exposing shrimp to nitrite concentration of 4 mg/L for 2 d reduced their growth but did not affect their survival.     

The determinants of detecting veterinary drug residues: Evidence from shrimp farmers in southern Viet Nam

While export-oriented shrimp farming has become an important source of income for many small-scale farmers in developing countries, the rate at which products are rejected at the ports of developed countries has remained high mainly due to the overuse of antibiotics. To reveal what determines the overuse of antibiotics, we interviewed 201 shrimp farmers in Viet Nam in 2015 and collected shrimp samples from each household’s pond for the screening of residual drugs. These tests revealed that residual drugs exceeding acceptable limits by Japanese standards were found in the samples of 40 farmers. We conducted cross-sectional Logit and Tobit regressions to examine whether results of the residue tests are significantly associated with farmers’ characteristics and management practices. This study finds that: (1) receiving BMP training has a significant and positive effect on reducing residual drugs; (2) if farmers know multiple extension officers, these relationships have significant and positive effects on reducing residual drugs; and (3) farmers with experience of shrimp disease outbreaks reduce use of antibiotics. Overall, this study contributes to revealing the determinants of detecting veterinary drug residues in shrimp farming in multiple (social, economic and psychological) dimensions.     

Effects of dietary astaxanthin supplementation on survival,growth and stress resistance in larval and post‐larval kuruma shrimp,Marsupenaeus japonicus

Two trials were conducted to evaluate the effects of chemically synthesized astaxanthin (Ax) on growth performance, survival, and stress resistance in larval and post‐larval kuruma shrimp (Marsupenaeus japonicus). Six dietary levels of Ax (0, 50, 100, 200, 400 and 800 mg/kg diet) were added to a baseline diet. As a first study, an 8‐day feeding trial was conducted on larval kuruma shrimp, with results showing that larvae‐fed diets supplemented with different Ax levels exhibited better performance during developmental and metamorphosis to postlarvae. Broken‐line regression analysis indicated that the optimal levels for growth and stress resistance of larvae were 168.9 mg/kg and 82.1 mg/kg diet, respectively. Second, a 30‐day feeding trial was conducted on post‐larval shrimp. Supplementation with 100 and 200 mg/kg Ax yielded significantly higher final body weight, body weight gain and specific growth rate than that in a control group. A cumulative mortality index for osmotic stress revealed significantly better performance in a group fed 200 mg/kg supplementation than in controls. Broken‐line regression analysis indicated that the optimal levels for growth and stress resistance of postlarvae were 108.7 mg/kg and 178.1 mg/kg diet, respectively. Based on these results, we suggest that carefully dosed Ax supplementation is a beneficial nutritional strategy for the early developmental stages of kuruma shrimp.     

Relative Abundance and Species Composition of Gram-Negative, Aerobic Bacteria Associated with the Gut of Juvenile White Shrimp Litopenaeus vannamei Reared in Oligotrophic Well Water and Eutrophic Pond Water

Gut bacteria may contribute significantly to the growth and survival of cultured shrimp, although little is known about factors that affect bacterial community structure in shrimp guts. The objective of this study was to determine the abundance and species composition of gut bacteria in juvenile white shrimp Litopenaeus vannamei reared in two different environments. Eight 120-L tanks were stocked at a density of 8 shrimphank. Two treatments were tested for 10 d and consisted of tanks receiving flow-through water from one of two sources: 1) well water pumped from a sea-water aquifer (Well treatment), and 2) pond water pumped from an intensive shrimp pond (Pond treatment). Shrimp mid- and hindguts were excised on days 1, 3, 6, and 10 for enumeration of gram-negative, aerobic bacteria by quantifying colony-forming units (CFU) using standard microbiological plating techniques. Identification of bacterial isolates was made using the Biologa® GN Microplate system. Bacterial numbers were significantly greater ( P > 0.05) in Well shrimp than in Pond shrimp on days 1 and 3. Following day 3, a decrease in bacterial numbers occurred in the Well shrimp, and no significant differences between treatments were observed on days 6 or 10. Guts from Well shrimp were dominated by Vibrio and Aero-monas , and these two genera accounted for 80–851 of the bacteria on each sampling day. Guts from Pond shrimp exhibited a greater bacterial diversity and were dominated by Vibrio, Aeromonas , and Pseudomonas. Flavobacterium were identified in the guts of Pond shrimp on days 3 and 10, but were not identified in any of the Well shrimp. A greater understanding of gut bacteria-shrimp interactions could lead to increased production and profitability for shrimp farmers through the development of more cost-effective feeds and novel disease control strategies.     

Effects of Integrated Shrimp Farming in Vietnam

Despite being a leading shrimp exporter in the world market, shrimp farming in Vietnam is carried out by many small‐scale farmers who face constraints in complying with increasingly stringent food safety and sustainability standards. The best way for such small farmers to circumvent this paradox is to make effective integrations both horizontally and vertically. Using value chain and institutional economics approaches, this study determines the factors that influence the probability of horizontal and vertical integrations between the production and processing stages in the shrimp industry in Vietnam. Analysis results confirm that integrated shrimp aquaculture is much more effective than the traditionally small‐scale‐ and individual‐production mode. In addition, logit estimation results identify the key factors affecting integration, including effectiveness of the legal framework, production scale, infrastructure development, and farmers' skill and awareness. Several policy recommendations proposed to encourage the development of integration in shrimp farming in Vietnam could also be useful for other similar developing countries.     

Forecast skill for predicting distribution shifts: A retrospective experiment for marine fishes in the Eastern Bering Sea

Forecasting distribution shifts under novel environmental conditions is a major task for ecologists and conservationists. Researchers forecast distribution shifts using several tools including: predicting from an empirical relationship between a summary of distribution (population centroid) and annual time series (“annual regression,” AR); or fitting a habitat‐envelope model to historical distribution and forecasting given predictions of future environmental conditions (“habitat envelope,” HE). However, surprisingly little research has estimated forecast skill by fitting to historical data, forecasting distribution shifts and comparing forecasts with subsequent observations of distribution shifts. I demonstrate the important role of retrospective skill testing by forecasting poleward movement over 1‐, 2‐ or 3‐year periods for 20 fish and crab species in the Eastern Bering Sea and comparing forecasts with observed shifts. I specifically introduce an alternative vector‐autoregressive spatio‐temporal (VAST) forecasting model, which can include species temperature responses, and compare skill for AR, HE and VAST forecasts. Results show that the HE forecast has 30%–43% greater variance than predicting that future distribution is identical to the estimated distribution in the final year (a “persistence” forecast). Meanwhile, the AR explains 2%–6% and VAST explains 8%–25% of variance in poleward movement, and both have better performance than a persistence forecast. HE and AR both generate forecast intervals that are too narrow, while VAST models with or without temperature have appropriate width for forecast intervals. Retrospective skill testing for more regions and taxa should be used as a test bed to guide future improvements in methods for forecasting distribution shifts.     

Manufacturing Different Diet Sizes and Its Effect on Pellet Water Stability and Growth of Three Size Classes of Pacific White Shrimp,Litopenaeus vannamei

Abstract

A feed manufacturing method involving the production of large pellets followed by crumbling to desired diet sizes was used to produce six shrimp diets to determine its effect on growth of three size classes of Pacific white shrimp, Litopenaeus vannamei. The six diets containing 45% protein were 0.7 mm crumble, 1.2 mm crumble, 1.7 mm crumble, 2.2 mm crumble, 2.6 mm crumble, and 3.0 mm pellet. These diets were fed to three size classes of shrimp subjected to a four-week growth trial under indoor laboratory conditions. Stocking density was 12 shrimp/aquarium for size class 1 (1.13iö.01 g), 9 shrimp/aquarium for size class 2 (7.31iö.06 g), and 6 shrimp/aquarium for size class 3 (13.12iö. 10 g). Shrimp were fed three times daily and were evaluated for live weight, growth rate, feed conversion ratio (FCR), and survival. Results for shrimp growth appeared to be affected by diet size and pellet water stability. The effects of diet size, however, were more evident on smaller sized shrimp. Weekly growth rates for class 1 and class 2 shrimp indicated significant responses (P < 0.05) to the effects of diet size, while the class 3 shrimp did not show any significant result. The growth rates for both class 1 and class 2 shrimp were lowest at the smallest diet size (0.7 mm crumble) but differed with respect to highest growth rates. The largest diet (3.0 mm pellets) yielded the highest growth rates for class 1 shrimp, while medium sized feed (2.2 mm crumble) produced the best growth for class 2 shrimp. This could be partly attributed to pellet water stability, which had a direct correlation to diet size (r = 0.97). Smaller diet sizes resulting from crumbling larger pellets tend to have lower water stability. The water stability decreased from 82.5% to 76.3% as the 3.0 mm pellets were reduced to 0.7 mm crumbles. Stress cracks are created during crumbling, and surface area to volume ratio are increased as larger particles are reduced to crumbles. These would make smaller diet particles more susceptible to disintegration and nutrient leaching. For class 3 shrimp, the largest pellets produced the highest growth rate. This high growth value, however, was not significantly different (P > 0.05) from growth results produced by the crumbled feed sizes. This observation suggests that diet sizes ranging from 0.7 mm crumble to 3.0 mm pellet could be used for a 13 g shrimp, although preference would be given to larger pellets due to higher growth performance and better pellet water stability. Results for shrimp live weights were similar to results obtained for weekly growth rates. FCR and survival of all shrimp sizes did not show any significant response from the effects of various diet sizes. However, larger shrimp were less efficient in their diet utilization than smaller shrimp.     

Impact of Long-term Training and Extension Support on Small-scale Carp Polyculture Farms of Bangladesh

One of the unique features of the Development of Sustainable Aquaculture Project of the WorldFish Center, Bangladesh, was the provision of 3 y of continuous training and extension in support of the fish farmers involved. It was expected that the long-term support would make a significant contribution to boosting production and incomes as well as sustainability. The article demonstrates the impact of the training and extension support to small-scale carp polyculture farmers in terms of productivity, profitability, and efficiency. The study used data collected from 225 project farmers and 123 control farmers during 2002/2003 to 2005/2006. The results show that the project farmers achieved an average growth rate in productivity terms (kg/ha) of about 23% per annum compared with only 3.8% among control farmers. Estimated annual return on investment per demonstration farm exhibits 52% higher return over the 3-y intervention period. During 2002/2003 to 2005/2006, the average technical efficiency score of project farmers increased from 0.55 to 0.86 compared with an average increase from 0.67 to 0.78 among control farmers over the same time period. The results showed that the efficiency gains and resulting increased productivity came from the development of human capital through long-term efficient and effective training and extension support.     

Shrimp Yields and Economic Potential of Intensive Round Pond Systems

Three intensive growout trials using Penaeus vunnumei were conducted in round ponds in Hawaii in 1987. A 337 m² experimental pond was stocked at 100 shrimp/m² for two trials; a 2,000 m² commercial prototype pond was stocked at 75/m² for one trial. In the experimental pond trials, shrimp survival averaged 88 ± 10% (SE) and feed conversion averaged 2.2 ± 0.2. Growth averaged 1.5 ± 0.3 g/week, yielding 18.2 ± 1.7 gram shrimp in 80 ± 5.5 days. Combined production in the experimental trials was 32,272 kg/ha in 174 days (from stocking of trial 1 to harvest of trial 2). Comparing these results to 1986 results (Wyban and Sweeney 1988), it was concluded that shrimp growth is not affected and production is doubled by increasing stocking density from 45/m² to 100/m². Pooling data from 1986 and 1987, a significant linear regression was obtained when weekly growth of shrimp above four grams individual size was regressed on mean weekly pond temperature: growth = 0.37 * temperature - 8.44, (r²= 0.41; P < 0.01). Multiple regression to examine effects of shrimp size, pond biomass, and shrimp age on the temperature-growth relationship was not significant. In the commercial prototype pond trial, survival was 67% and feed conversion was 2.0. Growth averaged 1.4 g/week, yielding 18.1 gram shrimp in 88 days. Production was 9,120 kg/ha. Individual shrimp size distribution at harvest in the commercial pond was similar to experimental pond results, indicating that shrimp growth in the two systems was comparable. Financial characteristics of a hypothetical 24 pond shrimp farm using these results were determined using an electronic spreadsheet model (hung and Rowland 1987). Feed costs were 40% of total operating costs while postlarvae and labor were 14% and 16% of total operating costs, respectively. Breakeven price (BEP) was far more sensitive to changes in revenuedetermining inputs such as survival and growth than to comparable changes in costdetermining inputs such as feed and postlarvae costs. Together these results suggest that commercial scale round pond production mimics experimental scale production and that round pond technology has commercial potential.     

Environmental determinants of perch (Perca fluviatilis) growth in gravel pit lakes and the relative performance of simple versus complex ecological predictors

Growth of fish is an important contributor to individual fitness as well as fish production. Explaining and predicting growth variation across populations is thus important from fundamental and applied perspectives, which requires knowledge about the ecological factors involved in shaping growth. To that end, we estimated environment-dependent von Bertalanffy growth models for 13 gravel pit lake populations of Eurasian perch (Perca fluviatilis) from north-western Germany. To identify the main drivers of perch growth, we evaluated the performance of 16 different biotic or abiotic lake variables in explaining growth variation among lakes. In addition, we compared growth predictions from the best-performing model incorporating “complex” variables that require intensive sampling effort, with a model using only “simple”, easily measurable lake variables (e.g. shoreline development factor). The derivation of a simple model aimed at future applications in typically data-poor inland fisheries, predicting expected growth potential from easily measurable lake variables. A model combining metabolic biomass of predators, maximum depth and shoreline development factor performed best in predicting perch growth variation across gravel pits. All three parameters in this model were positively related to perch growth. The best-performing simple model consisted only of the shoreline development factor. Length-at-age predictions from both models were largely identical, highlighting the utility of shoreline development factor in approximating growth potential of perch in gravel pits similar to our study lakes. Our results can be used to inform fisheries management and restoration efforts at existing or newly excavated gravel pit lakes.