Fish Assemblages As Indicator Of Water Quality Biology Essay

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Fish communities are more frequently used to assess quality or to monitor environmental changes in estuarine environments. The estuarine environment, owing to its dual marine and fresh water characteristics, supports a wide faunal diversity (Dreux, 1986; Mauvais and Guillaud, 1994; Bachelet et al., 1997) and its biological productivity is high. Fish assemblages are very varied, composed of true estuarine, amphihaline or euryhaline species (Marchand and Elie, 1983; Elie et al., 1990; Mauvais and Guillaud, 1994; Elliott and Dewailly, 1995; Methven et al., 2001).

Estuaries play a vital role in the functioning of both marine and inland aquatic systems by providing many marine, migratory or estuarine species with basic requirements for their life cycle (Potter et al., 1986; Elie et al., 1990), such as key habitats for reproduction, feeding, growth or physiological preparation for migration (Mc Dowall, 1988). Due to their position within the drainage basin, these environments are among the most impacted by human activities (Hostens and Hamerlynck, 1994; Maes, 2000; Cabral et al., 2001).

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Length-weight relationship gives a great importance in fishery assessment (Garcia et al.,1989). Therefore, the length and weight measurements with age data can give information on the stock composition, age at maturity, life span, mortality, growth and production (King, 1996; Diaz et al., 2000). Other than that, the length-weight relationship also useful in stabilizing the taxonomic characters of the species as well as important in management and exploitation of fish population (Pervin & Mortuza, 2008). Besides, the length-weight relationship is crucial for the studies on biology, population and management of species and their fisheries (Le Cren, 1951; Shafi and Quddus, 1974).

The length frequency data fish will be analyzed using special program package for length-based stock assessment called FiSAT II (FAO-ICLARM Stock Assessment Tools - Version 1.2.2). This software will be developed for detailed analysis of length frequency data and other related analyses for example catch at age, size at age, selection and data collected for tropical fish stock assessment (Gayanilo et al., 1997).

Water serves a multitude of uses. As the various uses have grown in diversity, constrained by the more or less fIXed quantity available, significant interaction of uses and reuses of water has also developed. Water quality is a very broad term when used by some people and quite specific for others and is the complementary aspect of water quantity (Biggar, 1979). Chemically pure water rarely occurs in nature. Its content varies largely from region to region, and is a reflection of the local geography and climate (Hynes, 1970). According to Tanji Key to authors' name: A. Suki; M. Kemil; T.P. Mok (l979), water is often referred to as a universal solvent and because of this solvent power, it tends to pick up impurities as it comes into contact with gases, liquids and solids.

In a developing country like Malaysia, rapid changes are continually taking place. These include population growth, urbanisation, agricultural, mining and logging activities, and industrialisation.

These changes bring about complex environmental problems and the most important natural resource that is affected is water (Abu Bakar, 1985). The development of land and natural resources, and the discharge of waste products into the water body are the main water pollution sources in Malaysia especially at Sungai Merbok in Kedah.

Objectives of the study

The objectives of the study are:

To describe the current fish assemblages in Sungai Merbok

To study the length-length and length-weight relationship of fish at Sungai Merbok

To study the monthly water qualities (physical and chemical) pattern in the Sungai Merbok

To analyse the effects and influences of the monthly water qualities fish species in the estuary waters of the Sungai Merbok.

ii. Literature Review

Fish assemblages

Fish population can be analyzed using length-weight relationship. Length and weight data are useful standard results of fish sampling programs (Morato et al., 2001). In fish, size is generally more biologically relevant than age, mainly because several ecological and physiological factors are more size-dependent than age-dependent. Consequently, variability in size has important implications for diverse aspects of fisheries science and population dynamics (Erzini, 1994). Length-weight regressions have been used frequently to estimate weight from length because direct weight measurements can be time-consuming in the field (Sinovcic et al., 2004).

One of the most commonly used analyses of fisheries data is length-weight relationship (Mendes et al., 2004). The length-weight relationship can be done by measuring the length and weight of fish taken at a particular time because fish can continuously change either in their length or weight. Length-weight relationships (LWR) provide basic information in fisheries biology, being useful to determine the weight of an individual fish of known length or total weight from length-frequency distribution, and to compare specific growth among different regions (Froese, 1998; Koutrakis and Tsikliras, 2003). This relationship was initially used to obtain information on the growth condition of fish and to find out whether the somatic growth was isometric or allometric (Le Cren, 1951; Ricker, 1973). Other than that, by using length and weight data, one can predict the fish growth parameters as well as predict the mortality rate which is useful in fish stock assessment (Samat et al., 2008).

Water Quality

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The quality of water required to maintain ecosystem health is largely a function of natural background conditions. Some aquatic ecosystems are able to resist large changes in water quality without any detectable effects on ecosystem composition and function, whereas other ecosystems are sensitive to small changes in the physical and chemical makeup of a body of water and this can lead to degradation of ecosystem services and loss of biological diversity. The degradation of physical and chemical water quality due to human influences is often gradual, and subtle adaptations of aquatic ecosystems to these changes may not always be readily detected until a dramatic shift in ecosystem condition occurs. For example, in many shallow European lakes, the gradual enrichment of the surface water with plant nutrients has resulted in shifts from systems that once were dominated by rooted aquatic plants to systems that are now dominated by algae suspended in the water column (Scheffer et al. 2001). Regular monitoring of the biological, physical, and chemical components of aquatic ecosystems can serve to detect extreme situations in which the ability of an ecosystem to return to its normal state is stretched beyond its limit.

Typically, water quality is determined by comparing the physical and chemical characteristics of a water sample with water quality guidelines or standards. Drinking water quality guidelines and standards are designed to enable the provision of clean and safe water for human consumption, thereby protecting human health. These are usually based on scientifically assessed acceptable levels of toxicity to either humans or aquatic organisms. The scientific and regulatory research community use to identify natural background conditions for chemicals that are not toxic to humans or animals and to use these as guidelines for the protection of aquatic life (Robertson et al., 2006; Dodds and Oakes, 2004; Wickham et al., 2005). Other guidelines, such as those designed to ensure adequate quality for recreational, agricultural or industrial activities, set out limits for the physical, chemical, and biological composition of water needed to safely undertake different activities.

Methodology

Fishing Operation and Sampling locations

This research is located at the estuary of Sungai Merbok in the district of Kuala Muda in Kedah It therefore has the advantage of being sheltered from the strong wind and waves. It is easily accessible from major towns like Sungai Petani, Alor Star and Butterworth. Moreover, since it is situated near Tanjung Dawai.

Generally, the fishermen in Merbok and Kuala Muda applied the artisanal fishery. The data about the fishing operation in these areas will be collect by interviewing the fishermen. Fishermen gave the required information about fishing vessels and boats, fishing gears and fishing operation. The data will be collect and noted by using the form in a table. Majority of fishermen in Kuala Muda use the trammel net or 'pukat tiga lapis' to catch the fish. Trammel nets are monofilament and consist of three layer of mesh. The outer mesh size will be 10.2 cm and inner mesh size will be 3.8 cm. The function of three layers will be to 'secure' the fish from escaping and fish will entangle. The net length will be 120 meters and net width will be 3-4 meters. This net floats vertically on the headrope and weighted on the groundrope. Trammel nets are most common as stationary gear, but they can also be used drifting. The fish entangle themselves in a pocket of small mesh webbing between the two layers and large meshed walls. Afterwards, the trammel nets are hauled back to the surface for extracting the entangling fish from the netting.The fishermen in Merbok usually used barrier net or 'pukat kering' to catch the fish. The barrier net will be set up during low tide and prefer lowest tide day and night operation. During high tide, fishermen use boat by pulling headline above water level and secure the net to the poles. The catches will be collected during low tide.

Prior to length, weight and other measurements, the fishes will be taken out from the freezer and allowed to thaw. The total length (TL) of each fish will be taken from tip of snout to longest ray of caudal fin. In other words, total length is the maximum length of the fish. Then, standard length (SL) will be measured from the snout to the end of vertebral column. Fork length (FL) measured from the tip of the snout to the end of the middle caudal fin rays. The total length, standard length and fork length measured in centimeters using a measuring board. Lastly, the body weight (BW) in grams will be measured to the nearest 0.1 gram using electronic weighing balance.

Length-Weight Relationships

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The length-weight relationship will be determined by using the data on the measurement of length and weight of Arius argyropleuron. The graph plotted by excel format (XY scatter) with total length (TL) on x-axis and body weight (BW) on y-axis. The length-weight relationship can be expressed by using equation:

W = aL b ( Le Cren, 1951; King, 1995; Froese, 2006)

Where W = weight of the samples in grams (g),

L = length of the sample in centimeters (cm),

a = constant (intercept)

b = constant (slope of regression line)

The value of a and b may change with age, sex, seasons and location (Froese, 2006). In fisheries practice, knowledge of length-weight relationship is very useful in fish stock assessment and for fisheries management (Sparre and Venema, 1992). The above equation can be transformed into linear form by using equation:

ln W = ln a + b ln L ( Arshad et al., 2008)

All data on total length (TL) and body weight (BW) transformed into ln TL and ln BW. Then the graph plotted with ln TL on x-axis and ln BW on y-axis in order to get the linear graph form instead of exponential form.

Water Qualities Sampling and Analysis

Water quality parameters (temperature, salinity, turbidity, dissolved oxygen, conductivity, pH and Total suspended solid [TSS], chlorophyll-a, biological oxygen demand [BOD], phosphate, nitrate and ammonia) of seawater around the sampling sites will be collect and measured for both surface and bottom water. Water qualities data is obtained once a month with two replicate at every station during the sampling of jellyfish to allow the determination of the exogenous environmental factors effect on the monthly distribution and abundance of jellyfish species in the estuary of the Sungai Merbok. Measurements of salinity, dissolved oxygen, pH, conductivity and temperature are recorded in-situ. Other parameters are analysed in the laboratory from the water samples collected.

Table 1 List of equipments used for water qualities measurements.

No

Parameters

Measurements' equipments/ methods

Unit

1

Temperature

YSI 85 DO-SCT meter

°C

2

Salinity

ppt

3

Conductivity

mS/cm

4

Dissolved Oxygen

mg/L

5

pH

6

Turbidity

Secchi Disc

metre

7

Total suspended solid

Standard manual method, APHA (1995)

mg/L

8

Chlorophyll-a level

Spectrophotometer

mg/L

9

Biological oxygen demand

5- Days BOD Test, APHA (1995)

mg/L

10

Phosphate, PO43-

Method by Strickland & Parsond (1972)

mg/L

11

Nitrate, NO3-

12

Nitrite, NO2-

13

Ammonia, NH3

Species Identifications

Species Checklist

3 months Specimen Sampling

Water Qualities Sampling

Field Measurements

Length

Weight

Composition

Length-weight relationship

In-situ analysis

Phosphate

Ammonia

Nitrite

Nitrate

TSS

BOD

pH

Temperature

Salinity

Conductivity

Dissolved Oxygen

Turbidity

Sites Survey/ voucher samples collection

Ex-situ analysis

Sampling Flow Chart

Gantt chart

Year 1

No.

Activities

Year 1

J

J

O

S

O

N

D

J

F

M

A

M

1.

Site survey/ voucher samples collection and preservation

X

X

X

2.

Species Identification

X

X

X

X

X

X

3.

Species Checklist

X

X

X

X

X

X

4.

Field sampling and measurements

X

X

X

X

X

X

X

X

X

X

X

X

5.

Fish assemblages collecting data ,Water qualities sampling & laboratory analysis

X

X

X

X

X

X

X

X

X

X

X

X

6.

Field data & result analysis

X

X

X

X

X

X

X

X

X

X

7.

Progress report writing

X

X

X

X

Year 2

No.

Activities

Year 2

J

J

O

S

O

N

D

J

F

M

A

M

1.

Field sampling and measurements

X

X

2.

Fish assemblages collecting data ,Water qualities sampling & laboratory analysis

X

X

3.

Field's Data and result analysis

X

X

X

X

X

X

X

4.

Progress report writing

X

X

X

5.

Final thesis writing

X

X

X

X

X

X

X

X

X

6.

Publication (Journal & presentation)

X