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Aspects of the behaviour of adult Atlantic salmon in estuaries, while on their spawning migration has been investigated using a salinity telemetric system. Eighteen fish were tracked in total in different Scottish estuaries. Studies involving the displacement of salmon from freshwater back into higher salinities on the River North Esk, Montrose showed fast movement through the estuary back into freshwater (5h), movement being initiated by the sensing of low salinities or the start of the flood tide. Tracking in the Dornoch Firth at Bonar Bridge (a channel type estuary) showed fish maintaining one position against both flood and ebb tides, experiencing salinities fluctuating widely about the isosmotic point. The qualitative assessment of salmon on passage through the estuary of the freshwater discharge of a non-natal river was also demonstrated, repeated entries of a very brief nature (21s) being recorded. The position held by salmon whilst on suspended migration in an estuary was recorded, no sampling of the freshwater discharge being undertaken on a tidal basis. The resting metabolic rate of farmed salmon of different stages of sexual development was recorded in saltwater, and on transfer to freshwater. Maturing fish exhibited a raised metabolic rate in saltwater, suggesting increased osmoregulatory costs. This was in contrast to non-maturing fish. The cannulation of wild salmon subjected to fluctuating salinities was undertaken. Plasma electrolyte levels and osmolalities of fish subjected to cyclic salinities were intermediate between salt-adapted and freshwater-adapted values, showing only small fluctuations. An inability to osmoregulate successfully in high salinities following 'stress' events was recorded in maturing farmed and coastally caught wild salmon, suggesting a maladaption to that environment. By contrast, non-maturing farmed salmon exhibited a greater degree of euryhalinity. Examination by electron scanning microscopy of apical pit structure of gill chloride cells supports the idea that increasing maturity or freshwater exposure reduces tolerance to saltwater. It is concluded that Atlantic salmon are euryhaline during at least part of their oceanic feeding phase, and on arrival in coastal waters on the spawning migration require no period of acclimitisation to freshwater. A reduction in tolerance to high salinities linked to advancing maturation/ freshwater exposure would thus serve to ensure river entry.

Thesis (M.S.)--Bowling Green State University, 2007. / Document formatted into pages; contains vi, 26 p. Includes bibliographical references.

Spring chinook salmon, Oncorhynchus tshawytscha, in the Snake River Basin are listed as endangered under the Endangered Species Act. The typical life history of spring chinook salmon is semelparous. An experiment was performed to see if mature male spring chinook salmon parr could be reconditioned after hand-spawning and spawned in successive years. The mature male parr were part of a 1997 and 1998 cohort of captive broodstock from the Grande Ronde River Basin in Oregon. Force-feeding was combined with volitional feeding in an attempt to inhibit senescence and increase survival time after spawning. The viscerosomatic index, fat and protein contents increased with survival time after spawning for both cohorts. There was a significant relationship between percent weight change and survival time for the 1997 cohort (p<0.001). Force-feeding had no effect on survival time after spawning for the 1997 cohort (p=0.074) or the 1998 cohort (p=0.178). Fat content, weight gain and survival time indicated that the reconditioning process was observable in the 1997 cohort at 77 days after spawning and was cyclical, resulting in a physiological response which allowed male chinook salmon to spawn in successive years. Fertilization trials with three reconditioned males yielded a fertilization success rate of 96.9% compared to 95.7% for 4-year old, anadromous male spring chinook salmon (p=0.152), measured as production of eyed-embryos. This experiment provides new knowledge of plasticity in the reproductive biology of male, stream-type, spring chinook salmon. Reconditioning and spawning male chinook salmon parr in successive years could be used to help maximize genetic diversity and aid in the recovery of endangered Oncorhynchus populations. / Graduation date: 2002

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Sexual condition of female Hilsa was sampled from October 1983 to August 1984 from freshwater, estuarine and marine localities in Bangladesh. At Chandpur, on the River Meghna, changes in gonadosomatic index showed that early monsoon (June), late monsoon (October), and winter (February) are the major spawning periods. Ages of juvenile Hilsa were determined up to six months old (12 cm long) by counting daily growth rings of otoliths. Hatching dates of juveniles collected in different months were back calculated from otolith readings, and confirmed the existence of the three spawning peaks. Migratory movements of juvenile Hilsa in the River Meghna were studied from samples obtained by experimental beach seining, by experimental drift gill netting, and by fishermen's gear. Length-frequency analysis of fish from beach seines and from fishermen's catch indicated juveniles less than 8 cm in total length inhabit shore and shallow river areas (<10 ft depth). When juveniles attain a larger size (>7 cm) they migrate to the deeper river (>10 ft depth) in January. After reaching 12 cm, all disappeared from the deeper river in May. Their migration from the river towards the sea was indicated by the direction of gilling in experimental nets, and by mean length analysis of juveniles collected in the upper and downstream areas of the River Meghna. / Science, Faculty of / Zoology, Department of / Graduate

Aquaculture methods are limited for white crappie (Pomoxis annularis), reducing production potential. Therefore, reproduction methods, including induced spawning, sperm cryopreservation and out-of-season spawning, were developed in tank systems. A two week acclimation period (15°C; 3-5 ppt salinity) was necessary to reduce disease-related mortality. Afterwards, four spawning induction hormones and a control were examined to induce spawning. Luteinizing hormone releasing hormone analogue and salmonid gonadotropin releasing hormone analogue performed the best in terms of spawning success and %ertilization. Sperm cryopreservation was effective using Hanks or Ca2+ree Hanks balanced salt solutions with 10%-methanol or 5%-dimethyl-sulfoxide as a cryoprotectant, frozen at 40°C/min. Out-of-season spawning experiments manipulated photoperiod and temperature over 3-wk (9% spawning success; 11% fertilization) and 6-wk (16% spawning success; 55% fertilization) seasonal shifts. Post-experiment maturation data indicate that females were in an intermediate development stage. These experiments demonstrate the potential of advanced spawning techniques to improve annual production of white crappie.

Common snook, Centropomus undecimalis, is a popular game fish species that occurs throughout central and southern Florida, yet many questions remain unanswered regarding their reproductive strategies, including estimates of fecundity with relation to size, age, and condition of the female. These relationships are critical to improving stock assessments and fundamental to estimating spawning potential ratio, the measure by which snook are managed. Spawning snook were collected from a known spawning site, Rattlesnake Key, Tampa Bay, Florida, during three consecutive spawning seasons (2009-2011) and batch fecundity for snook was reported for the first time. Of the 43 females suitable for fecundity analysis, batch fecundity was highly variably and ranged from 258,913 to 2,663,737 eggs. The mean batch fecundity was (984,689 eggs/batch, median = 781,330 eggs/batch) and the mean relative fecundity was 465 eggs/gram body weight (median = 402 eggs/gram body weight). Average batch fecundity did not vary by collection year, despite a severe cold event in the winter of 2010, which killed about 25% of the spawning population. However, analysis of proximate composition indicated that liver lipid percent was significantly reduced in 2010, likely due to reduced prey availability, increased energetic expenditures, or both, while enduring and recovering from cold exposure. A significant positive relationship in 2009 between batch fecundity and condition was reported that entirely disappeared in 2010. Additionally, in a preliminary investigation, we detected sub-population differences between known-spawning `bay fish' and `river fish' using barium as an indicator of freshwater habitat usage via otolith microchemistry. Our results are directly relevant to enhancing stock assessments and indicated that reproductive strategies of snook are both complicated and robust. Future research should further investigate reproductive strategies (e.g. skipped spawning) and possible sub-population life history, as both can have significant impacts on stock assessment models.

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