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The treatment performance of a 6 m wide by 67 m long by 0.8 m deep, baffled sedimentation basin receiving rainbow trout ( Oncorhynchus mykiss ) raceway effluent was evaluated with and without the installation of artificial substrates (Aquamats ® ). Treatment efficiency was also determined using normal rearing condition effluent loading versus cleaning and harvesting events. Total suspended solids (TSS) removal for the total basin averaged 79% and 71% during normal rearing conditions, as compared to 92% and 79% during cleaning and harvesting operations, when the Aquamats ® were installed versus removed, respectively. Total phosphorus (TP) removal by the total basin, with and without Aquamats ® , was 20% and 23% during normal rearing conditions as compared to 55% and 65% under cleaning and harvesting conditions, respectively. Higher TP removal during cleaning operations was attributed to sedimentation of particulate fractions. Dissolved nutrient removal ( ortho -phosphate (OP), total ammonia nitrogen (TAN), nitrate, nitrite, and total organic carbon (TOC)) was not consistent throughout the basin and did not improve when the Aquamats ® were installed. A short contact time and periphyton grazing by isopods may have limited the capacity of the Aquamats ® . Calculated retention times with and without Aquamats ® for the first half and total basin were 37% and 32% and 27% and 17% less than theoretical values, respectively based on a rhodamine WT dye study. Average surface overflow rates were adjusted accordingly and measured 19.1 m 3 /m 2 day when the Aquamats ® were installed, versus 14.8 m 3 /m 2 day when the Aquamats ® were removed for the overall basin. These rates are lower than previous recommendations for treating aquaculture effluents, but resulted in high solids removal and consistently low TSS effluent (average 2 mg/L by 50%. For the first half of the sedimentation basin, the overflow rate averaged 44.1 m 3 /m 2 day with Aquamats ® versus 35.8 m 3 /m 2 day without Aquamats ® . The majority of effluent treatment occurred within the first half of the basin, which was responsible for 84% and 94% of overall TSS removal, 42% and 100% of overall NH 3 -N removal and 61% and 80% of overall TP removal during normal and cleaning/harvesting conditions, respectively.

The leaching of nutrients from settled rainbow trout ( Oncorhynchus mykiss ) sludge into overlying water was evaluated over a 7-day period. Nutrient leaching was assessed in a stagnant reaction tank and one agitated by aeration to simulate turbulent conditions in stocked production raceways. Leaching of total phosphorus (TP), ortho -phosphate (OP), total Kjeldahl nitrogen (TKN), total ammonia nitrogen (TAN), and total organic carbon (TOC) occurred rapidly during the first 24 h in both stagnant and agitated conditions. The highest 24 h leaching occurred in the agitated tank, and power regression equations accurately described the varying rates of increasing TP, OP, TAN and TKN. In the stagnant tank, linear increases of TP, OP, TKN and TAN concentrations occurred during the first 24 h. These linear increases continued from days 2 to 7, but at slower rates than occurred during the first 24 h. Average nutrient leaching rates (mg leached/g sludge-h); (dry weight basis) were calculated based on linear concentration increases. In the agitated tank, nutrient concentrations decreased after 60 h, as aerobic bacterial uptake and/or chemical precipitation was suspected. Therefore, average leaching rates could not be determined. These findings reveal that daily cleanout of settling areas could eliminate the release of TP, OP, TAN, TKN, and TOC from settled solids by 66%, 65%, 39%, 76%, and 51%, respectively, as compared to weekly cleanout schedules. Sustained leaching rates indicate nutrient release will likely continue beyond 7 days. This information suggests aggressive and continuous sludge management is most beneficial for maintaining high water quality and regulatory discharge compliance in fish production.

Annually-spawning sunshine bass (Morone chrysops×M. saxatilis) were exposed to 6-, 9- or 12-month photothermal regimes. Abbreviated (phase-shifted) cycles were produced by excising photothermal conditions corresponding to May 17 to August 17 (9-month cycle), or May 17 to November 17 (6-month cycle), from a simulated annual cycle. Phase-shifted cycles reduced the interval between spawning and ovarian recrudescence, advancing gonadal maturation 2 to 3 months, and permitting off-season (December and January) spawning. Rapid gonadal growth began in June (6-month), July (9-month) and August (12-month cycle), coincident with decreasing artificial photoperiods and water temperatures. The offset in initiation of maturation persisted through final maturation, as females in the 6-, 9- or 12-month cycles matured after different periods of photothermal exposure (206, 240 and 268 days, respectively). Maximum oocyte diameters (855, 893 and 844 μm) were similar among females on all cycles. All females underwent final oocyte maturation (FOM) and ovulated after human chorionic gonadotropin (hCG) injection. Testicular growth among males on the three cycles began simultaneously (June). Maximum testicular diameters (11.2, 11.9 and 11.5 mm, respectively) were achieved after 153, 174 and 199 days in the 6, 9 and 12-month cycles, respectively. Milt was produced by >90% of the males in each treatment, and the duration of production was proportional to the cycle length, lasting 38, 42 and 91 days in the 6, 9 and 12-month cycles, respectively. Sperm concentration, duration of motility, and seminal fluid pH differed among males on the three cycles, but these differences produced no changes in fertilities, which averaged 69, 59, and 68% for fish on the 6-, 9- or 12-month cycles, respectively. All sunshine bass held on a second, sequential 6-month cycle developed mature gonads and were induced to spawn. However, peak oocyte and ovarian diameters were reduced and fertility was low (29%), suggesting additional time was needed for gonadal maturation. The good reproductive performance of fish exposed to 6- and 9-month phase-shifted periods indicates that shortened cycles are effective for inducing off-season maturation of sunshine bass, and suggests merit in evaluating the efficacy of phase-shifted cycles to advance maturation of higher-value striped bass broodstock.

Ultrasound images of the gonads of adult striped bass (Morone saxatilis) were recorded monthly to determine their efficacy in sexing and evaluating maturation status of broodstock throughout the year. The sex of adult (age V) broodfish was readily distinguished (95% accuracy) throughout the annual reproductive cycle. Adult (age II) female hybrid striped bass (M. saxatilis×M. chrysops) also were accurately (100%) sexed, whereas juvenile (age 1+) and adult (age II) male hybrids could not be accurately (42 and 45%, respectively) sexed with ultrasound. The maturational status of adult (age V) fish was readily differentiated throughout the annual cycle from cross-sectional measurements of gonad diameters on ultrasound scans. Maximum monthly ovary diameter ranged from a 11.4 mm in September to 26.3 mm at ovulation in March. Maximum monthly testes diameter ranged from 4.6 mm in July to 25.5 mm in March. Spermiating males exhibited larger mean (maximum) testicular diameters (23.5 mm) than non-spermiating males (13.1 mm). Maximum ovarian diameter was highly correlated (r=0.92) with oocyte diameter. Maximum gonad size, determined from scans of the entire gonad, proved to be a more consistent index of maturity than average gonad size. Ripe female and spermiating male striped bass can be characterized as having maximum ovarian and testicular diameters of > 30 and 20 mm, respectively, although fish with smaller gonads may be capable of spawning. Ultrasound is a simple, effective, and non-invasive method to sex and assess maturational status of adult striped bass and perhaps other commercially and ecologically valuable (endangered) species.