Regional Population Structure and Management of Aquaculture for Stock Enhancement of the Spotted Seatrout (\u3ci\u3eCynoscion nebulosus\u3c/i\u3e)

The spotted seatrout, Cynoscion nebulosus is one of the most popular game fish in coastal waters of the north central Gulf of Mexico. An aquaculture-based stock enhancement program that aims to supplement native wild populations in Mississippi was initiated in 2004 as part of management efforts to sustain stocks and provide additional fishing opportunities to anglers. A genetic program associated with stock enhancement is in development and seeks to assess the effects of stocking on genetic diversity and fitness of wild populations, and design and implement genetic management to monitor and minimize those impacts. In this work, the structure of spotted seatrout populations in the region was investigated in order to assist with the development of a sustainable spatial management of stocking operations. Spotted seatrout specimens were collected during 2010 and 2011 from the four major bay systems in Mississippi and from reference populations in Louisiana (Grand Isle), and West Florida (Pensacola and Apalachicola). Sample size per locality ranged from 53 to 105 specimens. All samples were assayed at 15 microsatellite markers. Divergence among bay systems from Grand Isle (Louisiana) to Grand Bay (Mississippi–Alabama border) was low and non-significant. However, significant divergence between these localities and the Apalachicola location (West Florida) was detected (0.0214 \u3c FST \u3c 0.0264, P \u3c 0.001), consistent with an isolation-by-distance model of population structure. Estimates of local effective population size by the linkage disequilibrium method were very large or infinite in most localities within the Western part of the sampled range (Mississippi and Louisiana) suggesting current population density is high in that region. While the lack of divergence among Mississippi bay systems supports genetic management as a single unit, further work is needed to determine the spatial scale of natural dispersal and assess the degree of local adaptation of regional populations

Atlantic croaker milt management in hatchery

The objective of this study was to optimize the methodology for spectrophotometric determination of sperm concentration in Atlantic croaker Micropogonias undulatus L. milt and to estimate its potential for short-term cold-storage. The spectrophotometric determination of sperm concentration was evaluated using milt samples from six males serially diluted in Hank's balanced salt solution at 200 mOsm kg 1 (HBSS). The predictive power of regression models between sperm concentration and absorbance was determined from 200 to 500 nm and found to be highest within the visible spectrum despite a peak of milt absorbance at 288 nm. Absorbance reading at 400 nm was selected for further analysis to maximize the absorbance of the sample hence the sensitivity of the method while minimizing the impact of potential sample contamination with blood. The standard-curve of correlation between sperm absorbance at 400 nm and concentration was validated and held an accuracy ranging between 7.40% and +4.56% across males. Total sperm motility duration and the proportion of motile spermatozoa were significantly higher in milt samples diluted 1:3 in HBSS than in the undiluted control during up to 30 h of cold-storage.The methodologies investigated in this study can be applied to optimize sperm usage and achieve predictable artificial fertilization protocols in Atlantic croaker

Effects of Annual Droughts on Fish Communities in Mississippi Sound Estuaries

© 2018, Coastal and Estuarine Research Federation. The Mississippi coastal region has two major rivers and four smaller rivers influencing the estuaries that make up the Mississippi Sound. The islands off Mississippi create a barrier which allows the area to be a widespread, productive estuarine region. With such a dependence on discharge from the drainages, it is important to understand the effect of salinity regimes on fish communities. Drought conditions in other regions have been shown to dramatically change the fish community structure. We used the long running Interjurisdictional Fisheries Program database (2006–2014) within Mississippi state waters and compared yearly fish communities between drought and non-drought years. Non-metric Multidimensional Scaling (nMDS), Analysis of Similarity (ANOSIM), and Indicator Species Analysis (ISA) were used to compare drought and non-drought conditions in the Mississippi Sound. During 2006 and 2007, which were identified as drought years by the Palmer Drought Severity Index (PDSI), differences in fish community structure were identified and compared to non-drought years (2008–2009 and 2011–2014). The ISA identified a total of eight species that were significantly influenced by drought years. Of the eight species, the abundance of seven species significantly decreased while the abundance of one species significantly increased. With an increasing human population in central and south Mississippi, pressure on freshwater resources is likely to increase, resulting in possible changes in the fish community dynamics of the Mississippi Sound. Understanding the influence of decreased river discharges will assist managers in determining the impacts of freshwater withdrawals during base flow periods