Wild Largemouth Bass Micropterus Salmoides Research Articles

Seasonal Carryover Effects following the Administration of Cortisol to a Wild Teleost Fish

Stress can have sublethal effects that are manifested either immediately or at spatial or temporal scales that are removed from the stress event (i.e., carryover effects). We tested whether a short-term elevation of plasma cortisol would result in seasonal carryover effects in wild largemouth bass Micropterus salmoides. Using exogenous hormone implants, we raised circulating cortisol concentrations in a group of wild fish for approximately 5 d in October 2007. We then compared activity (velocity, distance traveled) of cortisol-treated animals with that of sham-treated and control animals throughout the winter using an automated acoustic telemetry array. Immediately following treatment, the cortisol-treated fish showed increased activity relative to controls. However, this difference disappeared following the cessation of the elevation of circulating cortisol. During the winter of 2007 to 2008, the lake experienced a nearly complete winterkill event, providing insight into how a transient stress response can influence the response of wild animals to subsequent challenges. Most fish carrying acoustic transmitters succumbed during this winterkill event, but cortisol-treated fish died earlier than fish in other groups and showed a decrease in activity relative to controls and sham-treated fish before mortality. This study provides preliminary evidence of seasonal carryover effects in wild fish and yields insight into the ecological consequences of stress across broad temporal scales.

Long-term effects of surgically implanted telemetry tags on the nutritional physiology and condition of wild freshwater fish

Little is known about the long-term consequences of surgically implanted telemetry devices on wild fish, as they are rarely recaptured. We used wild largemouth bass Micropterus salmoides as a model to evaluate the long-term impacts of telemetry devices on fish physiology and nutritional condition in a closed freshwater lake where recapture rates were reasonably high. Between 2003 and 2005, 68 fish were surgically implanted with acoustic telemetry devices. Between 2005 and 2008, 17 of the tagged fish were recaptured after carrying a transmitter for 335 to 1402 d. Incision sites were examined, and individuals were non-lethally sampled for blood and measured prior to release. Plasma samples were analysed, and physiological measures of stress (glucose, Na+, Cl-, K+), tissue damage (aspartate aminotransferase), and nutritional status (Ca++, Mg+, phosphorus, total protein, triglycerides, cholesterol) were compared between fish carrying transmitters and temporally- and size-matched controls. Of the 17 recaptured fish, 3 retained at least 1 of the absorbable monofilament sutures and showed localised signs of inflammation and infection despite an elapsed time of 362 d post surgery. Five individuals showed signs of pressure necrosis at the incision site despite the fact that the transmitters averaged only 1.89% (range: 0.84 to 3.59%) of the body mass. There was no difference in any physiological parameter measured between the 2 groups, or within the telemetered fish, in relation to days since tagging or condition of the incision site. In summary, transmitter implantation was not correlated with any long-term change in any of the physiological parameters investigated. However, there is opportunity for additional research to optimise surgical techniques, guidelines on transmitter mass to body mass ratios, and choice of suture material to enhance the healing and long-term welfare of tagged fish.

A Survey to Determine the Presence and Distribution of Largemouth Bass Virus in Wild Freshwater Bass in New York State

During 2004 and 2005 a survey was conducted to investigate the presence and geographic distribution of largemouth bass virus (LMBV) in New York State. This iridovirus is widely distributed across the eastern United States; however, it had not previously been reported in New York State. Two hundred and eighty-three wild largemouth bass Micropterus salmoides and 8 smallmouth bass M. dolomieu were collected from 37 locations across the state. No clinical signs of LMBV or mortalities attributable to the virus were observed in the fish collected. Using a quantitative polymerase chain reaction (QPCR) method, we detected LMBV in 28 fish from 13 locations. Viral cytopathic effect in cell culture was observed in 5 fish from 3 locations. The virus isolated from cell culture was confirmed to be LMBV by an independent PCR method. Statistical analysis of the largemouth bass samples collected during 2005 revealed a wide difference in prevalence between the QPCR results and the cell culture results. Analysis of possible predictors, including age, sex, and month collected, showed no significant associations with the QPCR results. This survey confirms the presence and wide distribution of a potentially pathogenic form of LMBV in multiple water systems across New York State.

A Survey to Detect Largemouth Bass Virus among Fish from Hatcheries in the Southeastern USA

Largemouth bass virus (LMBV) is an iridovirus widely distributed in southeastern U.S. populations of wild largemouth bass Micropterus salmoides. However, this virus has not been previously reported from fish hatcheries. During 1999, 15 state hatcheries in 10 states in the southeastern USA were surveyed for LMBV. The virus was isolated from largemouth bass broodfish at five hatcheries, but juvenile largemouth bass were infected in only one of these facilities. There were no indications of the disease caused by LMBV in either adults or juveniles at the time samples were collected. The virus was not isolated in concurrent samples of forage fish from seven of the hatcheries, including three where LMBV was found. Although transmission of LMBV from infected populations to their offspring in hatcheries does not always occur, this virus could be spread by transport of infected broodfish or by stocking infected juvenile largemouth bass.