Commercial Diets in Phase I Palmetto Bass,Morone saxatilis × Morone chrysops,Production in Plastic‐lined Ponds: Fertilizer or Feed?

The role of offering a commercial pelleted diet has been characterized as both an expensive organic fertilizer and as a selected food item for larval hybrid striped bass (palmetto), Morone saxatilis × Morone chrysops, culture operations. In this study, we examined the effects of providing a commercial diet on fish production and zooplankton dynamics during phase I culture in plastic‐lined ponds. We also sought to estimate relative dietary contribution of a commercial fish feed relative to natural pond biota using stable isotope tissue analysis. Palmetto bass were stocked into six 0.04‐ha plastic‐lined ponds at a rate of 125,000/ha. During the 31‐d culture period, ponds were fertilized with alfalfa pellets at a rate of 112 kg/ha/wk. At 14 d post‐stock (dps), Silver Cup Trout Fry diet was offered at a rate of 13.6 kg/ha/d and fertilization was discontinued in three ponds. Although mean final fish length was significantly greater within the fed treatment, no other production parameters were found to be different (P < 0.1). Following feed application, copepod concentrations within the fed ponds were greater in magnitude by 24 dps. Through stable isotope tissue analysis, we found a significant enrichment in both ¹³C and ¹⁵ν of fish, zooplankton, and Chironomidae larvae within the fed ponds (P < 0.10). Using a three‐source mixing model, the mean (±SE) percent composition of feed in the fish's isotopic signature increased from 5% ±2 to 20% ±6 within 16 d. Although fish production was not greatly affected through the addition of a commercial fish feed, enriched ¹³C and ¹⁵ν of fish tissue indicate that palmetto bass fingerlings increasingly utilized the prepared diets over time. However, based on the isotopic values of fish and potential food sources, it can be estimated that natural pond biota likely accounted for up to 80% of nutrient assimilation in the hybrid striped bass.     

Replacement of fishmeal by fish protein hydrolysate and biofloc in the diets of Litopenaeus vannamei postlarvae

This study aimed to evaluate the effect of the gradual replacement of fishmeal with fish protein hydrolysate (FPH) and biofloc flour (BF) in the diets of white shrimp Litopenaeus vannamei postlarvae (2 mg). Five diets (420 g kg^?1 of crude protein) were formulated, and these replaced 0 (control), 10, 20, 30 and 40% (T0, T10, T20, T30 and T40, respectively) of the fishmeal. A commercial diet was used as an external control. The alternative ingredients FPH and BF were added at a ratio of 1 : 1. After 42 days, the shrimp survival was higher than 99% in all the treatment groups. A regression test indicated that the ideal fishmeal substitution level to obtain optimal zootechnical parameters (final weight, weight gain and protein efficiency) is between 15.16 and 16.5%. In this study, we demonstrated that BF and FPH are potential ingredients that can be used to replace fishmeal in L. vannamei postlarvae diets.     

Fundulus heteroclitus Gonadotropin(s) 2. Year-round husbandry of animals with active pituitaries and responsive follicles

Mummichogs (Fundulus heteroclitus) were exposed to various regimens of temperature and photoperiod in order to develop a routine husbandry procedure so as to have throughout the year a population of reproductively healthy fish with a good quantity and quality of prematuration follicles (1.2–1.5 mm) suitable for carrying out homologous bioassays ofF. heteroclitus gonadotropin. During the fall and winter months, wild fish in the field all had regressed ovaries (gonadosomatic index <1). On the other hand, laboratory-maintained fish, with or without cold temperature (15°C) and short photoperiod (10 h light/day) pretreatment, generally had sexually mature ovaries (GSI>10) when maintained on a warm temperature (25°C) and long photoperiod (14 h light) protocol. Ovarian follicles retrieved from laboratory fish were responsive toF. heteroclitus pituitary extract stimulation, and underwent germinal vesicle breakdown normallyin vitro. Hence these ovarian follicles served well as a bioassay forF. heteroclitus gonadotropin even outside of the normal breeding season. The pituitary glands retrieved from laboratory fish in winter also retained high gonadotropic potencies, in terms of maturational and steroidogenic activities. Our results thus demonstrated that active gametogenesis in laboratory-maintained fish can be extended five months beyond the end of the normal breeding season. Apparently,F. heteroclitus in Florida is potentially a continuous breeder when under favorable conditions, but has a reproductive quiescent period imposed upon it by some environmental stressor(s). Although the design of the present experiments did not determine the relative importance of nutritional factors, temperature, and photoperiod on the annual reproductive cycle ofF. heteroclitus, there are indications that diatary factors may play a much more dominant role in the reproductive cycle than previously recognized.     

Use of Microbial Flocs Generated from Tilapia Effluent as a Nutritional Supplement for Shrimp, Litopenaeus vannamei, in Recirculating Aquaculture Systems

Recovering nutrients in a fish effluent to be used as a supplemental feed for shrimp culture could ease constraints (e.g., environmental issues and high production cost) that have limited the US shrimp farming industry in the past. In this study under laboratory scale conditions, fish effluent was collected from a commercial tilapia farm and nutrients from the waste stream were offered as supplemental feed as either (1) untreated solids from tilapia effluent or (2) microbial flocs generated from the biological treatment of the effluent by reducing soluble chemical oxygen demand >80%. The first feeding trial demonstrated that microbial flocs contributed significantly (P < 0.05) to overall growth while untreated solids did not. Moreover, microbial flocs were larger and contained higher levels (P < 0.05) of protein. The second feeding trial investigated different feeding rates of commercial diets with and without microbial floc supplementation. Weekly measurements of mass and specific growth rates demonstrated that microbial flocs significantly (P < 0.05) contributed to shrimp performance. Weekly food conversion ratios were also reported. Water quality in shrimp systems during both studies was within safe levels, and no differences (P > 0.05) between treatments were observed for dissolved oxygen, nitrate‐nitrogen, nitrite‐nitrogen, pH, salinity, total ammonia nitrogen, and temperature.     

Physical oceanography of the North Carolina continental shelf during the fall and winter seasons: implications for the transport of larval menhaden

The circulation over the continental shelf off the southern Middle Atlantic Bight (MAB) and northern South Atlantic Bight (SAB) is examined for the fall and winter periods. Observational data are compared with results from a three-dimensional numerical model to identify the dominant processes on the shelf. By considering wind-forcing, tides, and a specified upstream inflow (into the MAB), the observed and modelled flow fields are in close agreement in the mid- and inner shelf regions. The resulting larval drift indicates a seasonal dependence of transport pathways from spawning grounds to estuarine nursery areas for menhaden larvae and other offshore-spawning estuarine-dependent fish. Specifically, the physical oceanography of the MAB and SAB during the fall and winter months suggests a north-to-south shift in spawning areas providing recruits to the Carolina estuaries, in agreement with the observed migration of the spawning populations.     

Influence of agriculture on in-stream habitat and fish community structure in Piedmont watersheds of the Chattahoochee River System

Abstract– Historical and contemporary fish collections were used to examine the influence of agricultural land use on fish communities in the central Chattahoochee River, USA. In-stream habitat data were also collected to examine the relationship between agricultural land use and stream habitat structure. We found a significant positive relationship between agricultural land use and in-stream sediment ( r ²=0.43, P =0.01). Stream depth heterogeneity decreased significantly with increased sediment ( r ²=0.39, P =0.02). Mainstream reaches draining agricultural lands had significantly lower levels of fish diversity than forested reaches ( r ²=0.47, P < 0.01). Agriculture also explained significant variation in mainstream species abundances but was not a significant predictor of species diversity or species abundances in headwater reaches. Most pool species that use coarse substrates decreased in relative abundance with increasing agriculture in the watershed. Our results suggest that mainstream environments and their associated communities are more susceptible than headwater reaches to the effects of agriculture. This finding has important consequences for conservation, since mainstream reaches are reported to function as species refugia during pulse disturbance events (e. g., floods, droughts).     

Feasibility of pacific white shrimp Litopenaeus vannamei culture in southern Brazil: effects of stocking density and a single or a double CROP management strategy in earthen ponds

Marine shrimp culture at southern Brazil is restricted to the warmer season (November to April). Therefore, farmers must consider culture strategies and competition with shrimp landings from artisanal fishery. The fishing season starts every 1 February; in order to obtain higher prices, farmers may consider shrimp culture in two crops, with a first harvest before the start of the fishing season, and a second harvest after the end of the landings. The present study evaluated the performance and feasibility of Litopenaeus vannamei reared at 10, 25 and 40 shrimp m⁻² either in two short consecutive culture cycles or one longer cycle (LC). The experimental design consisted of two sets of nine pens installed in a 3.8 ha earthen pond. In one set of pens, shrimp were harvested after 75 days and pens were restocked for another 75-day-long rearing period. In the second set of pens, shrimp were cultured for 150 days. Shrimp survival and final weight ranged from 79% to 91% and 6.67 to 14.53 g respectively. Feasibility analysis pointed towards culture at higher densities (25 and 40 shrimp m⁻²) in a LC as productivity (2274–4227 kg ha⁻¹) and shrimp final weight (13.05–13.21 g) resulted in higher profitability (US$7761–12 379).     

The contribution of diatoms to bioflocs lipid content and the performance of juvenile Litopenaeus vannamei (Boone, 1931) in a BFT culture system

This study aimed to evaluate the contribution of three diatom species on the lipid content of bioflocs, their permanence on the bioflocs and influence on the growth performance of juvenile shrimps. Juveniles of Litopenaeus vannamei were reared (30 days; three replicates per treatment) in biofloc systems inoculated with diatoms Amphora coffeaeformis (A), Cylindrotheca closterium (C), Conticribra weissflogii (W), or biofloc only (BF, chlorophycean rich). Water quality parameters were monitored daily and the microbiota on days 1, 10, 20 and 30. The lipid content and fatty acid profiles of bioflocs were analyzed at the end of the experiment. Shrimp survival rate (99%) at treatment A was significantly higher than at BF. The bioflocs in A treatment presented the highest lipid content, differing significantly from BF and W. The content of EPA (20:5) (n‐3) was significantly higher in A and lower in BF, while linoleic acid (18:2) (n‐6) was significantly higher in BF. The results indicate that high cell density of diatoms can be successfully maintained with silicate addition in biofloc systems and that the pennate A. coffeaeformis and the centric C. weissflogii are potentially better suited than the pennate C. closterium as food supplements for shrimp diets in biofloc nurseries system.     

Epitheliocystis in lake trout Salvelinus namaycush (Walbaum) is associated with a β‐proteobacteria

Lake trout Salvelinus namaycush (Walbaum) raised for stocking experienced yearly (2011–13) winter epizootics of epitheliocystis. Affected fish were dispersed on the bottom of the tank, had decreased feed and fright response, and mortality often reached 40%. Peak mortality occurred within 3 weeks of the appearance of clinical signs, and outbreaks typically lasted 6 weeks. Affected fish had no gross lesions but histologically had branchial epithelial necrosis and lamellar hyperplasia, with small to large numbers of scattered epithelial cells containing 10‐ to 20‐μm inclusions. A longitudinal study was undertaken of one annual outbreak, and lamellar hyperplasia was most closely associated with mortality. The number of inclusions was statistically greater (P < 0.05) before and during peak mortality, but inclusions were present in low numbers before clinical signs occurred. Results of histochemical staining, immunohistochemistry and transmission electron microscopy supported the presence of a β‐proteobacteria rather than a Chlamydiales bacterium within inclusions. PCR primers to identify Chlamydiales did not give consistent results. However, the use of universal 16S rDNA bacterial primers in conjunction with laser capture microdissection of inclusions demonstrated that a β‐proteobacteria was consistently associated with affected gills and is more likely the cause of the disease in lake trout.