Performance Of Cod Research Articles

COD removal of phenolic wastewater by biological activated carbon-sequencing batch reactor in the presence of 2,4-DCP

Treatment performance of COD in the presence of 2,4-dichlorophenol (2,4-DCP) was explored by using a biological activated carbon-sequencing batch reactor (BAC-SBR) system. Two COD levels of basic substrate were synthesized with a mixture of phenol and 2,4-dichlorophenol. Although effluent concentration was increased with reduction of sludge retention time (SRT) from 8-days to 3-days, treatment efficiency was indicated more than 90% of COD in all SRTs applied. Reactors operated with acclimated sludge could be expected to cope with quite high loading of inhibitory substances.

Individual variation in competitive performance of juvenile cod and its consequences for growth

This communication reports on experiments, which studied the variation in competitive performance of juvenile cod (Gadus morhua L.) and their growth rates. The fish were held in groups of five in either summer or winter conditions and tested for their individual response to prey offered sequentially. There was marked individual variability. Fish that took the highest share of prey tended also to be those that took prey earlier than others. In winter conditions these fish were the largest, but in summer conditions size had no effect. There was a positive influence of the indices of competitive performance on individual growth rate but the relationship was not significant

Aerobic and anaerobic swimming performance of individual Atlantic cod.

Individual Atlantic cod (Gadus morhua) were exercised using three different measures of swimming performance. (1) An endurance test (critical swimming speed, U(crit), protocol) designed to assess predominantly aerobic endurance swimming (duration hours). (2) An acceleration test (U(burst)), in which the fish were required to swim against a rapidly increasing current until exhausted (duration minutes). This test was designed to assess predominantly glycolytic-based swimming capacity. (3) A sprint test that examined the animals' ability to swim away from a sudden stimulus (duration seconds). Rates of oxygen consumption ( mdot (O2)) during the endurance test and various morphological variables of the individual fish were also measured. Both aerobic and anaerobic swimming performance of individual cod were found to be significantly repeatable over a 3 month period. mdot (O2) during the U(crit) protocol was also significantly repeatable at intermediate to high swimming speeds, but not at low speeds. Our results support extrapolation from metabolic rates at incremented swimming speeds to zero activity as the best way to measure standard metabolic rate in cod. While performance in the U(crit) test and the sprint test were positively correlated, there was a negative correlation between performance in the U(crit) test and performance in the U(burst) test. This implies a potential trade-off in individual cod between stamina and the ability to use glycolytic-based locomotion. Inter-individual variation in swimming performance during these protocols, while substantial, was not correlated with individual variation in fin surface areas, age or morphology. However, U(burst) performance was dependent upon the sex of the animals, while performance during the U(crit) protocol was significantly correlated with their aerobic scope for activity.

Osmotic performance and survival of Atlantic cod ( Gadus morhua) at low salinities

This study examines the capacity of Atlantic cod ( Gadus morhua) to withstand exposure to low salinities ranging from 1 to 7 g/l. Cod were exposed to hypo-osmotic waters (1, 3, 5 and 7 g/l water salinity) at 10°C over a period of 6 days. Mortality rate, changes in osmotic parameters and changes in plasma glucose were monitored as indices of stress. No cod survived more than 20 h after transfer to 1 g/l water salinity, while survival rate increased to 5% in the 3 g/l treatment, to 95% in the 5 g/l treatment and to 100% in the 7 g/l treatment. The 1–7 g/l range in water salinity brought about a gradation in the osmotic response. Plasma osmotic and ionic concentrations dropped sharply in the first 48 h of 1, 3 and 5 g/l treatments. Cod surviving exposure to 3 g/l had low ionic and osmotic concentrations, similar to those of moribund fish, whereas fish in the 5 g/l treatment returned, after 5 days, to higher concentrations close to the average for animals kept in 7 g/l salinity. Cod in the 7 g/l treatment maintained concentrations slightly lower than the average for control fish throughout the experiment. Plasma glucose concentration decreased considerably, in both the control and experimental treatments. The rate of decrease was lower at 7 and 28 g/l salinities than at 1, 3 and 5 g/l salinities. Blood glucose does not appear to be a reliable osmotic stress indicator in Atlantic cod.

The physical effects of an acoustic tag on the swimming performance of plaice and cod

Drag measurements in a small flume show that the Mitson-West transponding acoustic tag developed at the Fisheries Laboratory, Lowestoft, has a frontal drag coefficient CD0 = 0·6. For fish moving at constant speed the ratio of fish drag to tag drag is given by D/d = 0·82L2CD, where CD is an appropriate drag coefficient for the fish and L its length in cm. Acoustically tagged plaice, Pleuronectes platessa (36–52 cm length), and cod, Gadus morhua (50–70 cm length), tracked by sector-scanning sonar in the southern North Sea have been observed to swim at speed of 1 to 2 L S−1 through the water. Calculations with theoretical and experimental values of CD show that the smallest of these fish could have been slowed down by 7% and the majority by rather less than 5%. The extra ower output required for a tagged fish to maintain the same steady speed as an untagged fish is between 3% and 5% and to maintain the same constant rate of acceleration less than 1%. The results suggest that the swimming performance of plaice and cod observed by sector-scanning sonar is unlikely to have been affected in any significant way by the addition of the acoustic tag.