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Freshwater fish communities are a vital component of wild riverine ecosystems. The changing morphology typically offered by a river depends upon physical characteristics, including the nature of substrates, is exemplified by zonation theory proposed by Huet (1949).
The structure of a fish community is determined by the species present, their relative abundances, their life stages and their size distributions, and their distributions in space and time (Lek,S. et.al ). Natural Variability in fish communities can be attributed to differences in land elevation, water temperature, water chemistry, food resources and physical habitat (Lek, S. et.al.).
Ecosystems will change to adapt gradually to the length of river systems, which establishes longitudinal zonation observed in fish communities (Huet 1949+1959). Longitudinal zonation concepts describe the changes in environmental properties of river courses and so fish zonation concepts can specify rather precisely how fish communities react to changing river properties (Bram, G. et.al 2003). Huet (1959) proposed the existence of four distinct fish zones, characterized by their dominant species: trout, grayling, barbell and bream (Allan, D 1995).
This zonation could be valuable for the drawing up of references and targets for river rehabilitation; the planning of riverine fish reserves and for the valuation of the current fish assemblage in a river (Bram, G. et.al 2003). Each Fish zone described below:
- Trout zone: represents the headwaters of the catchment, with a steep/high gradient; high energy flow, narrow valley with a lack of nutrients (Davies, C. et.al 2004). The soil consists of clean gravel, sand and locally a little silt. Much of the food available is in the form of plants and invertebrates (Davies, C. et.al 2004). The fish present in this zone are typical bullheads and trout’s.
- Grayling zone: fast flowing clear waters, with a greater width and depth, the water is a little richer in nutrients in comparison to the trout zone. The sediment includes mainly sands, silts and fine gravels, as well as the odd cobbles and boulders (Davies, C. et.al 2004).
- Barbel zone: wide, lotic, often clear waters. This is the middle reach of a river, running through sloping hills and the water is richer in nutrients than in the Grayling zone. The characteristic fish species of the Barbel zone require clean gravel for completing their life cycle (Bram, G. et.al 2003).
- Bream zone: stagnant or slowly flowing, clear or turbid waters. This is the traditional zone of the lowland river. The water is slightly nutrient-rich by nature. Natural meandering in the Bream zone can result in stagnant water bodies in the flood plains. The Bream zone used to be very dynamic in space and time because of the on-going ecological succession, creating a vast variety of habitats, including bare gravel bars, steep banks, sheltered waters with submerged vegetation, reed marshes and floodplain forests (Bram, G. et.al 2003).
Some fish species, in particular the embryo to juvenile stages, are sensitive to changes in water temperature, substrate composition, stream flow, or various water chemistry parameters, while others are tolerant to change in their environment (Lek, S. et.al.). Mature Atlantic salmon migrate through all these river zones, and even though the eggs and juvenile can be sensitive to certain characteristics, they are not restricted to one particular zone. The sediment type of a river may indicate where juvenile Atlantic salmon populations are located. The structural and functional variety of such fish communities can make them excellent indicators of water quality and provide an integrated view of water-body condition (Lek, S. et.al.).
Sediment type can indirectly affect food availability, dissolved oxygen concentration, predation and territorial areas. This lab based study will investigate what sediment type Atlantic salmon may prefer, which could help locate salmon populations in the wild by sampling the sediment; and help maintain the health and wellbeing of cultured salmon within lab environments. The ventilation rate of Atlantic salmon was used to identify which sediment the individuals preferred (associating high ventilation rate with stress). Juvenile Atlantic salmon were within the Parr phase of their Life cycle. The Atlantic salmon life cycle is illustrated in Fig(X) below:
(Shearer, W. 1992)
The eggs of the salmon are colonised within a cluster known as a Redd (Shearer, W. 1992). Alevin is the first stage, once salmon have hatched from the Redd, and still rely on the yolk sac as the primary source of nutrition.
The next stage is the Fry, which is the stage carrying from the independence after consuming the yolk sac (Shearer, W. 1992), to disperse from the Redd.
The next stage is the Parr, which is the phase of when the salmon migrate through freshwater as a smolt. Parr are the newly migrating smolts in freshwater ranging from 1-3 years, less than 4 years (Shearer, W. 1992). They later fully mature within the smolt stage. On occasion, male Parr may fully mature in freshwater, migrating downstream earlier and becoming more silver (smolt and are known as precocious Parr (Shearer, W. 1992). The Salmon used in this study are within the Parr phase of their life-cycle and are between 1-3 years of age.
Smolt is the next stage in the life cycle, which is the phase of which the Salmon migrates downstream and into seawater systems (Shearer, W. 1992). The Salmon are fully matured at this stage, being able to cope in the change of temperature and salinity. Post-smolt is the stage from departure from the river until onset of wide annulus formation at the end of the first winter in the sea (Shearer, W. 1992). The Salmon stage is the final stage of the life cycle. This stage can be classified differently depending on its age and how many winters it may survive (Shearer, W. 1992).
The variation of animal activity incurs energy costs, which has had great ecological importance (Millidine, K. et.al. 2008). This energy can be accurately measured through metabolic rates; however there can be limitations to measure metabolic rates. Various techniques have been used to estimate the metabolic rate, including doubly labelled water, oxygen consumption and measuring ventilation rate.
A study by Millidine (2008) study showed that in salmon, the relationship between ventilation rate and metabolic rate was well described by a significant positive linear fit across a range of activities at any given temperature. Other factors may come into play, such as food digestion, recent stress, however this did not affect the manner in which metabolic rate was related to ventilation rate.
The ventilation rate in this study was measured by observing the gills (opercular beats) of salmon individuals, since it was a cost effective, reliable method to obtain ventilation rate that could be done without disturbing the individuals. The sediment type was varied to perhaps show a sediment preference and explain the variation in ventilation rate.
In the natural environment shelters can be a valuable source, providing individuals to conserve and restore energy to ensure survival. Natural shelters can be formed by the river or simply be the sediment type present. Shelters primarily provide protection against harsh environmental conditions and predation (Millidine, K. et.al 2006). In fast flowing water systems, shelters provides a physical barrier at which individuals can be less mobile; from predators it can shade and camouflage to preserve the costs of individuals to adapt their colouration (Millidine, K. et.al 2006). Shelters can be a valuable source to protect individuals.
The absence/presence of a shelter may affect the ventilation rate of the salmon, since sheltering can be such a valuable attribute within the natural environment. This study included artificial shelters, to observe whether individuals use the shelter and whether their ventilation rate was affected.
Individuals fighting over a resource have opposing interests in the outcome of the contest, but they may share a common interest in the avoidance of injury. So there may be a potential for mutual benefits and cooperative visual signals between opponents to avoid the cost of injuries (O’connor 1999). Certain fish species are able to modify the colour and sometimes patterns of body regions in short periods of time (O’connor 1999). These visual signals are thought to be a means of communication from competitive and aggressive behaviour. The signals can be controlled by a means of nervous and hormonal control of the contraction and expansion of pigment cells (chromatophores) (O’connor 1999). The precise meaning of such signals is rarely understood and this study will investigate what the darkening signals, juvenile Atlantic salmon use, may represent.
The social system of salmonids in streams is very stable. A minority of fish are mobile, but most maintain the same small home ranges for prolonged periods (Kalleberg 1958). Within these small home ranges, some fish aggressively defend a territory while others adopt a floating strategy, avoiding conflict by living in the interstices between the sites occupied by more dominant individuals. There is some indication that body darkening is associated with territorial defence, as territory-holding salmon can become pale in overall coloration while fighting, but darken between bouts. However, there has been no detailed investigation of either the factors that determine darkening, or whether it is apparently being used as a signal (O’connor 1999). It is likely that darkening in subordinates receiving frequent attacks may be a result of extreme stress, which also indicates subordination to the opponent (O’connor 1999). Each salmon was isolated to show that darkening could be related to a stressed individual (one that has a high ventilation rate).
This study observes the colouration aspect of juvenile Atlantic salmon, to possibly associate variation in resting ventilation rate. A study from O'connor (1999), showed that the subordinates did not maintain their darker coloration after the initial contest, which suggests that darkening may carry an associated cost, such as increased conspicuousness and hence risk of predation.
Aim: To investigate what sediment types, within lab conditions, may affect the resting Ventilation Rate of juvenile Atlantic salmon (Salmo salar). Observe indications of stress, to investigate significant relations towards increased Ventilation Rates.
The Hypothesis, Null Hypothesis and Alternative Hypothesis are listed below:
- Hypothesis – Active Individuals will have an increased Ventilation Rate
Null – Activity of individuals does not affect the Ventilation Rate.
Alternative – Non-Active individuals will have an increased Ventilation Rate
- Hypothesis - As the weight of the individuals' increases, the Ventilation Rate increases
Null – Weight of the individuals' does not affect the Ventilation Rate
Alternative - As the weight of the individuals' increases, the Ventilation Rate decreases
- Hypothesis - As the sediment type increases in size (Sediment type from 1-5), the Ventilation Rate decreases
Null – the size of the sediment type does not affect the Ventilation Rate
Alternative - As the sediment type increases in size (Sediment type from 1-5), the Ventilation Rate increases
- A) Hypothesis - As the colouration of the Parr Marks darkens (increases from 1-4), the Ventilation Rate increases
Null – the colouration of the Parr Marks does not affect the Ventilation Rate.
Alternative - As the colouration of the Parr Marks darkens (increases from 1-4), the Ventilation Rate decreases
B) Hypothesis - As the colouration of the Oval Patches darkens (increases from 1-4), the Ventilation Rate increases
Null – the colouration of the Oval Patches does not affect the Ventilation Rate.
Alternative - As the colouration of the Oval Patches darkens (increases from 1-4), the Ventilation Rate decreases
C) Hypothesis - As the colouration of the Spaces Between Oval Patches darkens (increases from 1-4), the Ventilation Rate increases
Null – the colouration of the Spaces Between Oval Patches does not affect the Ventilation Rate.
Alternative - As the colouration of the Spaces Between Oval Patches darkens (increases from 1-4), the Ventilation Rate decreases
- Hypothesis - As the colouration of the Sclera (eye) darkens (increases from 1-4), the Ventilation Rate increases
Null – the colouration of the Sclera (eye) does not affect the Ventilation Rate.
Alternative - As the colouration of the Sclera (eye) darkens (increases from 1-4), the Ventilation Rate decreases
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