Dispersion, population dynamics and stock assessment of Caspian Sea prawns, genus Palaemon in Guilan Province coastal waters

Biological aspects, population dynamics and stock assessment of the Caspian Sea prawns Palaemon adspersus and Palaemon eleganse were investigated in Guilan coastal water of the Caspian Sea. Sampling was done monthly with a bottom trawl with mesh size of 3 mm in cod end in 0 - 5 m and 5 - 10 m depth in areas as Astra, Shafa Roud, Anzali, Chonchanan Chamkhaleh and Chaboksar during year 2002. Results of one year sampling showed that mean total length of Palaemon adspersus (pooled data) was 39.9±6.84 mm (X±SD) and mean wiegth was 1.133±0.67 g. The mean total length of females and males was 41.6±7.5 mm and 37.9±5.2 mm respectively and mean weight for the mentioned sexes was 1.353±0.65 g and 0.868±0.38 g respectively. There was significant differences in mean length and weight of females and males (P<0.05). The mean total annual sex ratio of males: females for this species was 1.4 and this sex ratio deviated significantly from 1:1 (X2, P<0.05) and biased towards males in the population of this species. The spawning season of Palaemon adspersus begins in April and ends in September with a peak in June . Mean fecundity of this species was 1994.5 ± 506.6 . The growth coefficients Loo and K for females were estimated as 58.5 mm and 2.3 /Year and for males as 55.9 mm and 2.6 /year respectively . The mean CPUA ( catch / Km2 ) for this species was 9.99 ± 33.2 kg / km2 and the correspondance biomass was calculated as 5067.7 kg in 0 - 10 m depth . The mean total length of Palaemon elegans (pooled data ) was 27.5 ± 5.7 mm (X±S.D) and mm and 24.01±4.18 mm respectively and mean weight for the mentioned sexes were was 0.553 ± 0.3 g and 0.237±0.15 g respectively. There was significant differences in mean length and weight of females and males (P<0.05). The mean total annual sex ratio of males:females for this species was 0.57 and in this species also sex ratio differed significantly from 1:1 (X2, P<0.05) and skewed towards females in the population of this species. The spawning season of Palaemon elegans extended from May to September with a peak in July . Mean fecundity of this species was 642.7±313.4. The growth coefficients LOO and K for females were estimated as 42.119 mm and 2.40 /Year and 33.87 mm and 2.50 /year for males respectively. The mean. CPUA ( catch/ Km2 ) for this species was 0.75±3.86 kg/km2 and the correspondance biomass was calculated as 382.1 kg in 0-10 m depth .

The fish stocks in Uganda aquatic systems: opportunities and challenges for transformation

The status of fish stocks in a water body at any one time is a function of several factors affecting the production of fish in that water body. These include: total number (abundance) and biomass(weight) present, growth (size and age), recruitment (the quantity of fish entering the fishery) including reproduction, mortality which is caused by fishing or natural causes, Other indirect factors of major importance to the status of the stocks include production factors (water quality and availability of natural food for fish), the life history parameters of the different species making up the stocks (e.g. sex ratios, condition of the fish, reproductive potential (i.e. fecundity) etc), Changes in fish stocks do occur when any of the above listed factors directly influence aspects of growth, reproduction and mortality and therefore, numbers and standing stock (biomass). In the exploited fisheries, major research concerns regarding stocks relate to the listed factors especially: estimates of stock abundance/biomass, the quantity of fish being caught,where the fish are caught, which species are caught (relative abundance)when the fish are caught, how the fish are caught. The balance between stock abundance and amount of fish caught provides the basis for intervention. Due to the diverse characteristics of the physical water environment, fishes are in general, not evenly distributed throughout a water body. Shallow and vegetated areas tend to support higher abundance and diversity of fish species. In addition, seasonal variations in fish abundance are so strong that fluctuations in catch have to be expected at fish landings.

Fish exploitation and changes in the fish community of Lake George, Uganda

Unlike Lake Victoria, the fisheries of Lake George have undergone gradual changes in the size and proportion of the major commercial fish species, the Nile tilapia (Oreochromis niloticus: cichlidae) in the last 40 years (1950-1989). The size decreased from an average weight of 900g in 1950 to 430g in 1989 while percentage contribution in commercial catches during the same period declined from 92% to 36%. The over all annual commercial catches though showed a steady increase from the period 1950 when the fishery was opened to intensive and controlled exploitation, consistently high catches were observed in the 1960s and 1970s followed by a general decline in the early 1980s to amore or less stable fishery in the late 1980s. These changes are attributed to increased fishing pressure especially on the nil tilapia and to increased use of smaller gill net mesh sizes lower than the recommended 127mm mesh. The changes in gill net mesh have brought O. leucostictus, acichlid, into commercial catches confirming that the 88.9mm mesh size nets are used by the commercial fishermen to harvest smaller fish species. The commercial catches are presently dominated by the piscivorous fishes,(over 60%) whose contribution was less than 10% during initial exploitation of the virgin fishery in 1950.The piscivorous fish are mainly caught using hooks and lines. The entire fishery is believed to be exploited close to the maximum. The above trends serve to show the impact of exploitation on fish species diversity. Quantitive and qualitative changes of the major fish species on lake George are due to exploitation pressure unlike Lake Victoria where it is a combination of both exploitations and impact of fish introductions. There has been no fish introduction in Lake George.

Effects of atrazine herbicide on physiological, biochemical and histological biomarkers of developmental stages of larvae and fry in Caspian kutum, Rutilus frisii kutum

To investigation of the toxic effects of atrazine on newly hatched larvae and releasing age fry of the Caspian Kutum, Rutilus frisii kutum, the 96h LC50 was determined as 18.53 ppm and 24.95 ppm, respectively. Newly hatched larvae were exposed to three sublethal concentrations of atrazine (1/2LC50, 1/4LC50 and 1/8LC50) for 7 days. Different histopathological alterations were observed in fins and integument, gills, Kidney, digestive system, liver and the brain of the exposed larvae. Fry’s were exposed to one sublethal concentration of atrazine (1/2LC50) for four days, and like the larvae’s, many histopathological alterations were observed in fins and integument, gills, Kidney, digestive system, liver and the brain of the exposed fry’s, too. Also, measurements of the body ions: Na+, K+, Ca2+, Mg2+ and Cl- in atrazine exposed larvae and fry’s compare to control groups showed that atrazine is changed the body ions composition. No significant differences were found in length growth rate, weight growth rate and the condition factor of the atrazine exposed larvae and fry. Immunohistochemical localization of the Na+, K+-ATPase in integumentary and gill ionocytes, showed no differences in dispersion pattern of the ionocytes in atrazine exposed larvae and fry, compare to control group. Measuring the dimensions of the ionocytes and counting the ionocytes showed that atrazine is affecting on ionocytes by mild increasing in size and mild decreasing in number. Ultrastructural studies, using SEM and TEM, showed that atrazine have significant effects on cellular and subcellular properties. It caused necrosis in surface of the pavement cells in branchial epithelium, necrosis in endoplasmic reticulum of the ionocytes and changed the shape of the mitochondria in these cells. Results showed that sublethal concentrations of atrazine were very toxic to larvae and fry of the Rutilus frisii kutum, and at these levels can made some serious histopathological alterations in their tissues. Related to the severe histopathological alterations in osmoregulatory organs, like gill, kidney and digestive system, and the alterations in the body ion composition, it could be concluded that atrazine could interfere with the osmoregulation process of the Rutilus frisii kutum at the early stages of the life history.