Molting and Mortality of Red Swamp and White River Crawfish Subjected to Eyestalk Ablation: A Preliminary Study for Commercial Soft-Shell Crawfish Production

Eyestalk ablation may reduce the cost of soft-shell crawfish production by reducing the molt interval. In this study, both immature and mature red swamp crawfish Procambarus clarkii and white river crawfish Procambarus zonangulus , formally Procambarus actus actus (Hobbs and Hobbs 1990), were ablated using a pair of modified pliers and placed in a recirculating system. Molting percentages, mortalities and mean molt intervals of the ablated crawfish were analyzed.
Eyestalk ablation resulted in dramatic reduction of molt intervals and mortalities comparable with the current commercial (non-ablation) soft-shell crawfish production systems. The mean molt intervals of the ablated red swamp crawfish ranged from 6.7 to 7.8 days for immature and 9.2 days for mature animals; whereas, the molt interval of ablated white river crawfish was 8.9 and 11.2 days for immature and mature animals, respectively. Mortalities obtained in this study ranged from 20 to 48% and 32 to 66% for immature and mature crawfish, respectively. During the experiments, molting percentages and mortalities were not consistent. Secondary treatments such as air clotting and cauterization did not alter mortality significantly.     

Molting,Mortality, and the Effects of Density in a Soft-Shell Crawfish Culture System 1

The molting and mortality patterns at a crawfish density recommended for commercial-scale soft-shell crawfish culture systems showed that, over a 116 day period, 74% of the crawfish molted, 22% died, and 4% remained in the system at the end of the study. Approximately three weeks of adaption to the system were required before molting rates of the crawfish began to increase. By the sixth week, the number of malted crawfish per day exceeded the overall mean and remained at this level until 10 days before moltable crawfish were depleted. In a second study, three density levels (3.7,4.9, and 6.1 kg crawfish/m²) were tested for 60 days. The lowest density produced significantly fewer (P < 0.05) molted crawfish. Mortality was significantly greater (P < 0.05) at the highest density compared with the lowest density. The highest density (6.1 kg crawfish/m²) showed a higher molting rate than the lower densities, but it was not significantly different (P < 0.05) from the molting rate of 4.9 kg/m².     

Retention of Intermolt Crawfish in a Hydraulic Soft-Shell Crawfish Separation Unit

Physcial configuration and operational parameters of a prototype hydraulic soft-shell crawfish separator tray are described. The tray takes adavantage of the inability of soft-shell crawfish to resist a continuous water velocity to effectuate their rapid separation from a mixed population of pre-molts and intermolts. Removal of molted crawfish is rapid, and research therefore has focused on retaining intermolts in the separation tray. Given a well desigend separation tray, intermolt loss rates were found to be prinipally controlled by flow rate and intermolt retention time. Electrical inhibition gates powered by twelve-volt alternating current were used to discourage downstream migration of intermolts through administration of a mild shock upon contact. Crawfish became condioned to avoid the tray exit to the extent that they would not voluntarily approach the inhibition gate.     

Effects of Added Substrate on Production of Red Swamp Crawfish, Procambarus clarkii, in Earthen Ponds without Planted Forage

The effects of addition of substrate consisting of plastic mesh fencing to experimental earthen ponds were evaluated for the culture of the red swamp crawfish, Procambarus clarkii, without planted forage. Mean daily yield (kg/ha/d), number of crawfish harvested (number/ha/d), and mean individual harvest weight were compared for ponds with and without substrate during a 2‐yr period. The surface area of added substrate was equivalent to 50% of the bottom surface area of the pond. Mean daily yield in the ponds containing substrate, based on a comparison with that of the previous year, increased by 80.2% and was principally attributed to a 66.7% increase in the number of crawfish harvested. Comparative values for the ponds without substrate were ?13.1 and ?11.7%. For the second year, the treatment‐dependent response was consistent. Mean daily yield for the substrate ponds increased by 48.8% compared to 15.0% for the ponds lacking substrate. The primary benefit of the substrate appears to be provision of refuge and three‐dimensional distribution of crawfish in the pond, thereby reducing the incidence of cannibalism and increasing the total number of crawfish harvested per hectare per day. The benefit of the substrate in a commercial production setting must be weighed against its cost and longevity as well as the conditions of the particular management scenario into which it may be incorporated.     

Predicting Crawfish Molting with Machine Vision

The objective of this project was to develop a vision system that could predict when crawfish will molt. Different sections of the crawfish shell were examined to determine how the color changed as the time of molting approached. A strip on the tail section of the crawfish showed the greatest, most consistent color change. The average red/green × red/blue ratio decreased for every crawfish as the molting time approached. Using this ratio as a predictor, it was possible to predict the molting of a crawfish within 3 d with an accuracy greater than 80%. The limitation on accuracy was primarily the result of the large variations in natural shell color among the crawfish.     

Diversification of Crawfish Management Schedule1

Six 0.02 ha ponds were used to evaluate crawfish production and standing crop biomass of rice forage in ponds managed on a standard (control) and delayed (experimental) schedule over a two year production cycle. Delayed schedule followed the same sequence of events except the management activities were delayed approximately one month. Control and experimental ponds had statistically similar amounts of forage. No statistical difference was detected in crawfish production between the management schedules or between production years; however, analysis revealed a significant treatment × year interaction. Overall average crawfish production was 986 kg/ha. Variation in crawfish production is explained within the context of annual temperature variations and differences in population density.     

Predation by Dragonfly Naiads Anax junius on Young Crawfish Procambarus clarkii

Anax junius (Odonata: Aeschnidae) predation on young crawfish, Procambarus clarkii , was measured in the laboratory. Predation rates (0.066–1.16 crawfish/day) were estimated at 25, 15, and 5 C and for two sizes of crawfish (11–20 and 21–30 mm total length). Naiad predation increased with increasing temperature and decreasing crawfish size. At 5 C, naiads had no significant effect on survival of large crawfish but did significantly reduce survival of small crawfish. At 15 and 25 C, predation rates were significantly affected by temperature and prey size. Relative naiad abundance in a 0.8 ha crawfish pond was estimated from September through May. Larger naiads (head width, >6.5 mm; total length, >30 mm) capable of preying on young crawfish were not present until after most crawfish had reached invulnerable sizes. Large naiads, as a result, may not affect crawfish production under normal management conditions.     

Double-Cropping Malaysian Prawns,Macrobrachium rosenbergii,and Red Swamp Crawfish,Procambarus clarkii

Prawns, "Macrobrachium rosenbergii," and crawfish, "Procambarus clarkii," were alternatively grown in ponds to determine if they were compatible and if total production could be increased. Brood crawfish were stocked into replicated ponds at rates of 0,60, 120 or 180 kg/ha on 18 April. Water was removed to encourage burrowing. Following this, rice was planted as forage. Post-larval prawns (0.02 g) were stocked 3 July in all ponds at 17,500/ha. Prawns in half the ponds were fed and those in the other ponds were not. Ponds were drained from 7 to 11 October. Prawn production ranged from 157 to 248 kg/ha; survival ranged from 69% to 88%, and average size ranged from 11 to 7 g. There was no significant difference (P > 0.05) between fed and non-fed treatments. The ponds were reflooded and crawfish were harvested by trapping from 15 January to 15 May. The average yield of crawfish ranged from 746 to 1,266 kg/ha. Stocking rate had no effect of crawfish yields (P > 0.25). Total yield, with prawns and crawfish combined, ranged from 1,037 to 1,237 kg/ha. Overall, prawns and crawfish were compatible in rotation. Prawns were a good size for soft shell production during months when crawfish are not available for soft shell production.     

Pond culturing of crawfish in the Southern United States

Due to a significant increase in the farming of crawfish by pond culture methods in the southern United States this paper briefly summarises the current practice being developed there.

Crawfish are cultured in shallow, open ponds surrounded on all sides by levees. The water depth seldom exceeds 45–61 cm. Area may vary, but the most popular sizes range from 2 to 16 ha. A rotation scheme involving rice and crawfish is generally practised, with rice serving as food for the crawfish.

Good management techniques are required for maximum crawfish production. One essential element is circulation of water through the ponds to keep dissolved oxygen concentrations above 5 mg litre⁻¹. With good quality water and proper management a harvest of up to 2200 kg ha⁻¹ yr⁻¹ may be realised.     

Effects of Population Density and Feeding Rate on Growth and Feed Consumption of Red Swamp Crawfish Procambarns clarkii

Wire-mesh enclosures were used in production ponds to conduct growth trials in which population density and feeding rate were evaluated in a 2 × 2 factorial arrangement for their effects on crawfish growth. Juvenile Procambarus clarkii of uniform size (0.5 g) were stocked at 2 or 20 animals/m² in experiment 1 and weighed biweekly for 12 wk. Rice forage served as the detrital base, and supplemental feed (25% crude protein) was provided at either a low (26–52 kg/ha per week) or high (104–418 kg/ha per week) rate. In experiment 2, mixed sizes of crawfish were stocked at 10/m² or 20/m² and fed the formulated feed at either 52 or 312 kg/ha per week. Feed consumption was estimated for each treatment combination. Only population density significantly affected crawfish growth. Mean weight gain and final weights were inversely proportional to density but only when total crawfish biomass exceeded 1,235 kg/ha. Growth was not significantly influenced by feeding rate, but the high feeding rate resulted in a significantly greater ratio of hepatopancreas weight to body weight and tended to decrease hepatopancreas moisture levels, indicating improved condition. Population density, feeding rate, and their interaction had significant effects on estimated feed consumption. From the simple linear regression of mean feed consumption on crawfish standing crop, it was estimated that crawfish consume about 0.1 kg of dry feed per ha per week per kg of crawfish biomass on a 5 d per week feeding schedule at mean water temperatures, ranging from 14 to 30 C.     

CHANGES IN CRAWFISH PRODUCTION COSTS AND CURRENT PRODUCTION PRACTICES USED

Louisiana State University Agricultural Center cost estimates for single-crop crawfish production costs are analyzed for the period, 1991–2010, to determine changes in the cost components of Louisiana crawfish production. Fuel costs have contributed the most and fixed expenses the least to increased production costs, with total expenses per acre increasing by an average of 3.8% per year if land is not included and by 3.6% per year if land is included. Crawfish prices have varied greatly over the period, ranging from $0.50/lb in 1993 to $1.75/lb in 2000. Production practices used by Louisiana crawfish producers are highly variable, creating challenges for estimating representative production cost estimates.     

Growth of Crawfish Procambarus clarkii as a Function of Density and Food Resources

This study utilized enclosures (cylindrical, 5-mm wire mesh, O.5 m² bottom surface area) placed over rice-forage substrates in experimental crawfish ponds to contain crawfish under typical pond culture conditions. Juvenile Procambarus clarkii were stocked at six densities (2, 4, 6, 10, 14, and 18 crawfish/m²) for 12-wk growth trials in October and again in February. Crawfish relied solely on the detrital food system for their nutritional needs. Supplemental feed was supplied to crawfish in additional enclosures at two of the test densities (2 and 10 crawfish/m²). The commercially formulated feed (25% crude protein) was fed (2.02 g dry feed/m²) 3 d/wk (Monday, Wednesday, Friday). All treatments were replicated with six enclosures. Crawfish growth was inversely correlated to culture density. Mean final weights for crawfish feeding from the detrital-system only were 15.3, 13.8, 11.2, 7.9, 7.2, and 5.8 g for crawfish densities of 2, 4, 6, 8, 10, 14, and 18/m², respectively. Mean final weights for crawfish receiving supplemental feed were 20.7 and 12.4 g for densities of 2 and 10 crawfish/m². When compared with density as a factor influencing growth, feed influenced growth less than density abatement. Supplemental feeding improved crawfish growth in detrital systems an average of 46%, while decreasing initial density improved growth an average of 80.5%.     

Evaluation of rice (Oryza sativa), volunteer vegetation,and alligatorweed (Alternanthera phyloxeroides) in various combinations as crawfish (Procambarus clarkii) forages

Four treatments of naturally occurring plants and planted rice were evaluated as forages in experimental crawfish ponds. Their relationships to biomass production, dawn dissolved oxygen, unstable water levels, and crawfish production were determined.Total standing biomass of forage at fall flooding was significantly lower (P < 0.01) for alligatorweed plus volunteer vegetation ponds compared with all other forage regimes. Average dawn dissolved oxygen during the first 5 weeks after flooding varied between 1.7 mg/l and 4.7 mg/l in ponds containing alligatorweed, compared with 1.0 mg/l and 1.5 mg/l in ponds containing other vegetation. Crawfish yields in kg/ha for ponds with stable water levels were: rice plus alligatorweed, 2852; rice only, 2652; rice plus volunteer vegetation, 2117. These forage treatments appeared to sustain the crawfish population, and stunting of crawfish at unmarketable sizes was not observed.     

An Analytical Model for Predicting the Carrying Capacity of Submerged Biofilters Used in Aquaculture

Laboratory data and information from the literature were used to develop an equation that models ammonia removal by submerged biofilters. The equation is based on the half-order/zero-order kinetics model and fixed biofilm nitrification, which indicates that the nitrification rate is a linear function of the ammonia concentration at ammonia concentrations <2.0 mg/l. Input data for the equation include easily gathered information of flow rate, biofilter size, maximum permissible ammonia level, biofilter influent and biofilter effluent ammonia concentrations, temperature, and ammonia production rate. The equation can be used to determine the carrying capacity of the submerged biofilters, to estimate biofilter sizes needed to support various fish loads, and to investigate the effects of changes in biofilter system parameters on carrying capacity. Comparisons of the predicted and actual carrying capacities of several experimental biofilters indicated that the equation accurately predicted carrying capacity under most conditions. Studies of the sensitivity of the equation to changes in system parameters demonstrated that flow rate limits biofilter performance and suggested an approach for determining cost-effective flow rates for biofilter operation.     

Effects of Water Quality,Weather and Lunar Phase on Crawfish Catch1

The relationship between water quality, weather, lunar phase and daily changes in crawfish (Proearnbums clurkii) catch per unit effort (CPUE) was determined in five experimental crawfish ponds from March through May, 1984 and 1985. Air and water temperatures, solar radiation, dissolved oxygen, wind velocity, barometric pressure, precipitation and lunar phase were recorded daily during the harvesting phase of the study. Crawfish CPUE (g/trap/24 h) was significantly correlated with water temperature, dissolved oxygen, lunar phase, barometric pressure, wind velocity and the relative density of harvestable size crawfish. Most statistically significant environmental or climatological variables explained less than 20% total daily variation in crawfish CPUE. The nine environmental variables were reduced to four factors—temperature-harvestable crawfish, cold fronts, rain showers, and lunar phase—with principal-components analysis. Eighty-five percent of the variation in daily crawfish catch was attributed to water temperature and relative density of harvestable crawfish, and 7.1% was explained by lunar phase. Rain showers and cold fronts accounted for 4.8 and 2.5% of the daily variation in crawfish CPUE, respectively. Crawfish catch increased with an increase in water temperature and relative abundance of harvestable crawfish, and with short duration rain showers. Conversely, crawfish CPUE declined with the approach of full moon and with passage of cold fronts.     

Effects of Supplemental Feeding on Harvest of Red Swamp Crawfish,Procambarus clarkii,in Forage‐based Ponds

Procambarid crawfish aquaculture in the USA relies on an established forage‐based system for providing sustenance for growing crawfish. These systems may become inadequate at times for providing sufficient nourishment to support maximum growth of the population. Supplemental feeding is not routinely used because management recommendations for the cost‐effective use of supplemental feeds in ponds are not available. Because crawfish under confinement readily consume and grow well when fed single feedstuffs, such as rough rice seed and whole, raw soybeans, this study was initiated to investigate the use of these readily available low‐cost feedstuffs as supplemental feeds in aquaculture ponds. Earthen ponds (0.2 ha), constructed and managed to simulate commercial crawfish ponds, were used over three consecutive production seasons to evaluate the effects of supplemental feeding on yields and size of crawfish. Treatments for Seasons 1 and 2 consisted of (a) hull‐on rough rice seed, (b) whole raw soybean, (c) formulated 25% crude protein pellet, and (d) no supplementation and were replicated in four and three ponds for Seasons 1 and 2, respectively. Treatments for Season 3 consisted of (a) whole raw soybean and (b) no feed, with 10 replicated ponds each. Feeding frequency was established each year, and feeding rates were adjusted according to predetermined guidelines and monitoring of feeding trays. Crawfish harvesting was conducted by baited wire‐mesh traps and all harvested crawfish were subjected to a mechanical grader and sorted into three size classes. Results show that supplemental feeding, while trap‐harvesting operations are underway, can reduce yields and generate a negative economic benefit, perhaps as a result of residual feed within the pond rendering the baited trap less effective.     

The Economics Associated with Crawfish Production from Louisiana's Atchafalaya Basin 1

Unpredictable water levels for the Atchafalaya River resulting from man's efforts to prevent flooding in South Louisiana lead to an unstable market for Louisiana's annual crawfish production. Empirical models presented show that yields from the basin can be estimated on a monthly basis using bimonthly changes in water level, unemployment rates, and crawfish harvests from ponds. The monthly demand model for basin crawfish yielded a price flexibility of –0.059 and a corresponding price elasticity of –16.94. These empirical results support hypotheses that substitutes for crawfish are available to consumers. Uncertain yields from the basin due to the sort of water level fluctuations documented in this study suggest that investment in this area of the Louisiana crawfish industry will continue to be hampered.     

USE OF A SEINE TO DETECT STUNTED CRAWFISH POPULATIONS IN PONDS,A PRELIMINARY REPORT1

A 4.5-m long bag seine was used to sample crawfish from six 0.04 ha experimental ponds. Length-frequency histograms were evaluated as a predictor of size structure and to detect stunted populations of crawfish. The findings demonstrated importance of determining size structure of crawfish in predicting stunting and harvest potential of a population. Distinct differences in size structure of crawfish populations were apparent by 6 and 12 weeks after flooding ponds. Crawfish populations, with over 45% of the individuals exceeding 75 mm total length after 12 weeks, produced 25 to 30% greater yields than populations in which less than 5% of the crawfish exceeded 75 mm at 12 weeks post-flooding.     

Different combinations of protein ingredients in carp diets for reducing phosphorus loading

ABSTRACT: This study was conducted to gather data on the reduction of environmental phosphorus (P) loading through the formulation of carp diets with different combinations of protein ingredients. Five experimental diets were formulated by substituting fishmeal (FM; 10–20%) with alternative protein sources such as meat meal (MM; 5–15%), blood meal (BM; 5–7%), and defatted soybean meal (dSBM; 6–10%). The control diet used was a commercial carp diet selected based on earlier experiments. Each diet was fed to duplicate groups of juvenile carp three times a day, until satiation for 12 weeks. Feed performance was proportional to the increase in dietary FM levels. Phosphorus absorption ranged between 41.6% and 52.0% among the experimental groups and was 42.6% for the control group, but there were no marked differences in nitrogen (N) absorption rates. Phosphorus retention ranged from 31.4% to 35.7% for the test diets, whereas N retention increased proportionally with dietary FM levels and ranged from 34.7% to 41.7%. The P and N retention values of the control diet were 27.6% and 41.2%, respectively. The total P loading (T-P) increased at the higher FM levels (9.1–10.7 kg/t production), whereas lower FM levels produced higher total N loading (T-N, 34.6–43.1 kg/t production), the figures for the control being 13.9 T-P kg/t production and 35.6 T-N kg/t production. These results indicate that the reduction of FM levels to 10–20% by replacing it with MM, BM, and dSBM in carp diets was effective in reducing the loading of P and N.     

TENANCY ARRANGEMENTS USED BY LOUISIANA CRAWFISH PRODUCERS

Land tenancy arrangements vary widely in the U.S. crawfish industry, including full ownership by the crawfish producer, cash leases, share leases, and combination cash-share leases. This study examines the array of tenancy arrangements available and analyzes the types of farmers selecting each using a multinomial logit model. Choice of tenancy arrangement varies according to a number of traditional factors, such as farm size, experience, specialization, and production system. The influence of production system on land tenancy selection is of particular interest. Crawfish-rice double-crop producers tend to own all of their crawfish land, while those farming under rotational systems with crawfish and field crops tend to select combination cash-share leases. Shares, rental rates, and percentages of pumping cost paid by the landlord vary widely.