Bar Grader Research Articles

Effect of Handling and Transport on Cortisol Response and Nutrient Mobilization of Golden Shiner, Notemigonus crysoleucas

Abstract As the most popular baitfish in the USA, the golden shiner is subjected to frequent handling and transportation episodes prior to retail marketing and recreational use. Considerable mortality and economic loss can occur during handling and transportation. Limited information is available concerning stress responses, such as cortisol secretion, and mobilization of nutrients, such as zinc and ascorbic acid, during handling and transportation of this fish species. Therefore, two concurrent experiments were performed to characterize cortisol responses, as well as changes in whole‐body zinc and visceral ascorbic acid concentrations, after harvesting, grading, and transporting by ground or air. During ground transportation, fish were sampled immediately after being subjected to the following conditions: seined from a commercial pond in Lonoke, Arkansas (I), released into vats from the loading truck (II), graded by bar grader (III), loaded onto a hauling truck (IV) and after transport for 10 h to Brenham, Texas (V). Fish were also sampled before and after air freight shipment. Whole‐body cortisol appeared to be a reliable endocrine marker for stress response of golden shiner subjected to handling and transportation. Grading by bar grader was the most stressful event in the process of handling and transporting golden shiners, resulting in a significantly elevated whole‐body cortisol concentration of 107 ng/g tissue, compared to concentrations of 6.3, 32.3, 15.7, and 30.4 ng/g tissue, for stages I, II, IV, and V, respectively. A significant increase in whole‐body cortisol concentration was also observed after air transportation of 22 h duration. No significant reductions in whole‐body zinc or visceral ascorbic acid concentrations were observed.

The economic feasibility of adoption of a new in-pond mechanical grader for food-sized channel catfish ( Ictalurus punctatus)

An economic analysis of an in-pond horizontal floating bar grader for food-sized channel catfish was performed. Data from previously reported field trials were used to determine whether farmer adoption of this grader is economically feasible. Scenarios for four farm sizes (65, 130, 259, and 478 ha) were evaluated. Partial budget, payback period, net present value, internal rate of return, and Taguchi quality loss function analyses were used to quantify and compare economic losses due to deviation from the target fish size. Partial budget results indicated positive net revenue for all farm sizes. Net revenue increased with farm size, market price, and increased dockage penalties. Payback periods ranged from 0.1 to 2.0 years depending on the scenario. Net present values were positive and increased with increasing farm size. Estimated internal rates of return were higher than the current opportunity cost of capital and increased with increasing farm size. The value of the gain in quality from reducing size variation from use of the UAPB grader was estimated to range from $770 to $5575/year, depending on farm size. Producer adoption of the UAPB grader is economically feasible for the scenarios analyzed.

A comparison of new in-pond grading technology to live-car grading for food-sized channel catfish (Ictalurus punctatus)

Grading trials were performed in experimental and commercial catfish ponds to compare an in-pond horizontal floating bar grader to current live-car grading. Three replicate trials were conducted in experimental ponds at three different temperature ranges (warm, >26°C; cool, 13–26°C; cold, <13°C) with catfish size groups stocked in ratios of either 75:25, 50:50, or 25:75 sub-marketable (<0.57kg) to marketable fish (≥0.57kg). Commercial pond trials were replicated three times at each temperature range with a fish size range typical of ponds ready to harvest. Stress experienced by fish during harvest and grading was measured by mean serum glucose and cortisol levels. Grading speed was greater (P < 0.05) with the UAPB grader (105–449kg/min) than the traditional live-car grader (0.5–0.6kg/min). The UAPB grader decreased (P < 0.05) the proportion of sub-marketable fish during all trials. In contrast, the live car did not reduce the proportion of sub-marketable fish with the experimental methods used in this study during commercial trials or in the 25:75 distributions during warm and cold temperature trials in experimental ponds. The UAPB grader returned an average two to four times (range of 2–52) more sub-marketable fish by weight to the pond than the traditional live car method. Glucose and cortisol levels in fish graded with the two technologies were not significantly different. The UAPB grader sorted fish more accurately, consistently, and quickly than the live car at all temperatures in both experimental and commercial trials.

Effects of stocking different fractions of size graded juvenile prawns on production and population structure during a temperature-limited growout period

Size grading of juvenile prawns prior to pond stocking is used to disrupt negative social interactions. Animals graded off the upper end of the size range can outperform ungraded animals by 20–50%. However, reports differ on the performance of the lower grade fraction. Some studies indicate that lower grade prawns can out perform ungraded populations within a 120–140-day growing season while other studies indicate that >140 growing days are required. The objective of this study was to compare the growth of this lower grade fraction with the upper grade fraction and an ungraded fraction of the same population within a temperature-constrained growing season of 100–120 days. Prawn juveniles that had been nursed 60 days were separated into three groups. Approximately 50% of the population was maintained ungraded with the full range of size variation. The other 50% was separated into two fractions (large=upper grade; small=lower grade) using a #13 bar grader (0.5-cm spacing). Ponds were randomly assigned to receive one of the three treatments (ungraded controls, upper grade, and lower grade) with average stocking weights of 0.5±0.3, 0.8±0.4, and 0.2±0.1 g ( x̄±S.D.), respectively. There were three replicate 0.04-ha ponds per treatment. All ponds were stocked at 59,280 ha −1. Artificial substrate was added to ponds at a rate to increase available surface area by 50%. After 104 days, there was no significant difference ( P>0.05) in survival of prawns from the three fractions (overall average 88%). Total production, marketable production (>20, >30 g) and average individual weight was significantly greater ( P<0.05) in prawns from the upper grade fraction. At harvest, there was no significant difference ( P>0.05) in total production or average individual weight of prawns stocked from the ungraded or lower graded fractions. Impacts of grading procedures on population structures were much more pronounced in females than in males with upper graded animals having a significantly higher ( P≤0.05) percentage of sexually mature reproductive females. Compared to ungraded juveniles, projected net returns were lower for lower graded prawns, higher for upper graded, and higher for combined lower and upper under all model farm scenarios. In summary, stocking of the upper graded fraction increased total production, average weights, and marketable production. There was no difference in lower graded and ungraded animal production variables.

A Low Cost Bar Grader for the Harvest of Hybrid Striped Bass (Morone chrysops x M. saxatilis)

Four bar graders were designed and built to separate a mixed-size population of market-size reciprocal cross hybrid striped bass Marone chrysops x M. saxatilis in rectangular culture tanks in an indoor, recirculating aquaculture system. Grader frames were constructed of 5.1 cm (2 inch) PVC pipe and fittings. PVC electrical conduit ( 1.27 cm, 0.5 inch) was used to form a series of parallel, equally spaced vertical bars within the frame. Bar slot spaces were 1.90, 2.54, 3.20, or 3.80 cm (0.75, 1.0, 1.25, 1.5 inches). A strip of flexible vinyl siding was attached to the outer edges of the bar grader to permit a tight fit between the grader and tank walls, and prevent fish from swimming around the grader. The graders were placed sequentially into one end of the tank, largest slot size first, and maneuvered to the opposite end. Each grader International Journal of Recirculating Aquaculture, Volume 3 5 remained in the tank for 60 min. Fish too large to pass through a grader were netted and measured for weight, length and width. Regression analysis was performed for average weight retained at each bar spacing (Y = 7.13619 + 0.070716 X; r2 = .9987). By rearrangement, an equation was derived which allows a culturist to select a bar spacing that retains fish of a predetermined weight : Grader bar slot size (mm)= Fish weight (g) -177.9 I 31.7) Construction of each grader required approximately 2 h, and materials cost $20.

Relation between Bar Grader Spacing and Golden Shiner Size

Abstract The average lengths and weights of golden shiners Notemigonus crysoleucas that were retained between a series of successively smaller bar graders were determined. Regressions that expressed the relation of the average fish sizes to the mean distance between the bars of the retaining graders were determined and expressed as graphs. Tables, constructed from these relationships, are presented and explained for practical use by baitfish farmers.

Effects of Stocking Density and Feed on Pond Production Characteristics and Revenue of Harvested Freshwater Prawns Macrobrachiurn rosenbergii Stocked as Size‐Graded Juveniles1

AbstractA nursery‐reared population of juvenile freshwater prawns (Macrobrachium rosenbergii) averaging 0.11 ± 0.058 g was size graded through a 4‐mm bar grader producing a numerically 53% upper size population (0.25 ± 0.086 g). These were stocked into triplicate earthen ponds (0.04–0.07 ha each) at densities of 39,540, 59,300 and 79,100/ha, grown for 131 to 134 d, and fed a specially formulated diet. An additional three ponds were stocked at 39,540/ha and fed a commercial sinking catfish feed. Density had a significant effect on average whole body wet weight at harvest but no significant effect on either total yield, survival, or feed conversion. Mean wet weight was significantly higher for prawns stocked at 39,540/ha (34.3 g) than that for those stocked at either 59,300/ha (26.7 g) or 79,100/ha (263 g). The direct relationship between the percentage of small males and increasing density usually seen with ungraded populations was not evidenced in the size‐graded populations. Average total yield ranged from 1,041 to 1,662 kg/ha for stocking densities from 39,540 to 79,100/ha. Differences in overall mean wet weight resulted from differences in mean wet weights for orange claw and no claw males and berried and open females, not from differences in morphotype distributions. These differences resulted in significantly higher percentages of tails within the larger count categories and higher revenues for prawns stocked at 39,540/ha. Feed type had no significant effect. Projected net revenues suggest that prawns need to be marketed and sold as a whole product.

Relation between Bar Grader Size and Size of Striped Bass

Abstract Regression equations and a table that express the relation between bar grader spacing and total lengths and weights were determined for 5–7-month-old striped bass (Morone saxatilis).

Operating and Design Criteria of an Adjustable Horizontal Bar Grader for Sorting Channel Catfish

Operating and Design Criteria of an Adjustable Horizontal Bar Grader for Sorting Channel Catfish