The current body of work on rearing larval/juvenile zebrafish is based on (1) utilization of freshwater and (2) diurnal light/dark cycle, (3) provision of live feed at modest density, and (4) culture in high visibility environment. We challenged these rearing approaches by maintaining zebrafish under constant light for 46-48 days (days postfertilization [dpf]), while securing continuous feeding in high turbidity and saline (1.8-2.1 parts per thousand) environment for the experiment's duration, allowing 24 h feeding/growth of fish from first exogenous feeding to maturation. There was no evidence of negative effects on zebrafish larvae behavior, growth, survival, and life cycle duration at constant illumination when food was continuously available. Zebrafish were stocked at high initial density (100 larvae/L) in a static system and fed high densities of rotifers (Brachionus plicatilis) (200-400/mL) from 6 to 12 dpf. Fish density was then reduced by 50% and two diet treatments, live rotifers or brine shrimp (Artemia) nauplii (10/mL), followed. Fish were reared on these two diets until first maturation. Performance of adult zebrafish fed live rotifer followed by Artemia nauplii diet was the highest recorded in the literature after 42 dpf, 250 ± 29 (males) and 430 ± 5 mg (females). Use of these rearing conditions, during the entire life cycle, until reproduction, resulted in the shortest ever recorded generation time (from egg to egg) of 43-45 dpf and fertilization rate (1 dpf) of 80.3%-94%.
The sperm of Yellow Perch Perca flavescens of two different age-classes, age 0 and 3, were cryopreserved using two different cryoprotectants (dimethylsulfoxide [DMSO] and methanol [MetOH]) with two freezing methods (pellet and vial). The viability and quality of the progenies obtained from fertilization with cryopreserved sperm were then examined. The motility of Walleye Sander vitreus sperm was examined following cryopreservation and ultraviolet (UV) irradiation, with the aim of using heterologous cryopreserved sperm to inseminate Yellow Perch eggs to ensure gynogenesis. The first experiment compared the motility of fresh sperm and pellet method cryopreserved sperm devoid of salmon seminal plasma. Despite the high motility of fresh sperm-75% and 100%-of males age 0 and 3, respectively, the postthaw motility of seminal plasma devoid cryopreserved sperm was 0%. The second experiment addressed the efficiency of pellet and vial freezing methods with DMSO and MetOH supplemented with salmon seminal plasma. Cryopreserved sperm was thawed and motility measured. Sperm motility was not significantly different between pellet (13.3 ± 10.4%) and vial (10.3 ± 12.9%) methods in the absence of sperm extender; however, sperm motility of the pellet method was further improved (20 ± 8.7%) with the addition of sperm extender after thawing, while motility of the vial method sperm (10 ± 7.1%) was not. Cryopreserved sperm was further evaluated based on fertilization rate and ultimate survival and growth of larvae and juveniles through 14 d posthatch. Effects of UV exposure on fresh and pellet method cryopreserved sperm following UV irradiation were also examined. The motility of control sperm cryopreserved with DMSO and MetOH, and UV-exposed sperm cryopreserved with DMSO decreased from 100% motility before cryopreservation (fresh sperm) to 75% following cryopreservation, while UV-exposed sperm cryopreserved with MetOH decreased from 100% to 50%. This experiment provides significant new data to improve the effectiveness of straightforward cryopreservation techniques for Yellow Perch.Yellow Perch Perca flavescens is a North American game fish as well as an important species to aquaculturists. Advancements in artificial spawning, incubation and hatching of perch embryos, and larviculture over the past few decades have promoted the development of Yellow Perch aquaculture; however, several challenges and
A laboratory experiment was carried out to quantify and compare the physical damage (measured as scale loss), recovery and survival of two size categories [small: 48-85 mm total length (TL); large: 78-148 mm TL] of 0-group mulloway, Argyrosomus japonicus, after simulated escape through square-shaped mesh (bar length of 21.5 mm). Regardless of their size, fish that were fatigued to exhaustion and forced through square meshes sustained significantly more (i.e. >1.8 times) scale loss than did control fish that were only fatigued. However, the total scale loss incurred was <5% and significantly improved 7 days after treatment. Survival rates over a 2-week observation period were 100 and >97% for treatment and control fish, respectively. The results support the utility of square mesh for reducing the prawn-trawl fishing mortality of unwanted bycatch.
The tolerance of eyed‐stage embryos of Walleye Sander vitreus to cooling at melting‐ice temperatures and their subsequent hatching and rearing to advanced juveniles were examined. Embryos (71% viable; 8 d after fertilization) were refrigerated in an insulated transportation Styrofoam box between wet cheesecloth layers and melting ice (1.4°C) for 25, 48, 72, and 120 h. Embryos were then acclimated to 14°C aquaria for hatching and rearing (20°C). The hatching of embryos and their ability to continue development (swim bladder inflation), food acceptance (live nauplii of brine shrimp Artemia spp.), and growth were monitored for 14 d. The duration of exposure to cold storage stress resulted in no significant differences in mean ± SD survival (46.8 ± 8.0, 38.7 ± 8.6, 41.0 ± 4.9, and 36.9 ± 12.5% for 25‐, 48‐, 72‐, 120‐h treatments, respectively) at the end of the rearing and feeding period. However, the proportion of fish with inflated swim bladders was the highest in the 120‐h cold‐delayed fish (mean ± SD = 61 ± 18, 54 ± 8, 64 ± 3.8, and 90.5 ± 8%, respectively). The mean weight of fish was not significantly influenced by cold storage treatments but was significantly influenced by swim bladder status (9.2–11.8 mg, 7.0–9.8 mg, and 5.7–9.5 mg for fully inflated, partially inflated, and uninflated groups, respectively). This experiment provides significant new data to fish culturists regarding the storage of Walleye embryos prior to hatching and the possibility of convenient transportation or delayed stocking of larvae into prepared nursing ponds or indoor rearing tanks for intensive culture.
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