Age determination and growth of the night shark (Carcharhinus signatus) off the northeastern Brazilian coast

Age and growth of the night shark (Carcharhinus signatus) from areas off northeastern Brazil were determined from 317 unstained vertebral sections of 182 males (113–215 cm total length [TL]), 132 females (111.5–234.9 cm) and three individuals of unknown sex (169–242 cm). Although marginal increment (MI) analysis suggests that band formation occurs in the third and fourth trimesters in juveniles, it was inconclusive for adults. Thus, it was assumed that one band is formed annually. Births that occur over a protracted period may be the most important source of bias in MI analysis. An estimated average percent error of 2.4% was found in readings for individuals between two and seventeen years. The von Bertalanffy growth function (VBGF) showed no significant differences between sexes, and the model derived from back-calculated mean length at age best represented growth for the species (L∞=270 cm, K=0.11/yr, t0=–2.71 yr) when compared to the observed mean lengths at age and the Fabens’ method. Length-frequency analysis on 1055 specimens (93–260 cm) was used to verify age determination. Back-calculated size at birth was 66.8 cm and maturity was reached at 180–190 cm (age 8) for males and 200–205 cm (age ten) for females. Age composition, estimated from an age-length key, indicated that juveniles predominate in commercial catches, representing 74.3% of the catch. A growth rate of 25.4 cm/yr was estimated from birth to the first band (i.e. juveniles grow 38% of their birth length during the first year), and a growth rate of 8.55 cm/yr was estimated for eight- to ten-year-old adults.

Spatial and temporal patterns in the demersal fish community on the shelf and upper slope regions of the Gulf of Alaska

We analyzed data from National Marine Fisheries Service bottom trawl surveys carried out triennially from 1984 to 1996 in the Gulf of Alaska (GOA). The continental shelf and upper slope (0–500 m) of the GOA support a rich demersal fish fauna dominated by arrowtooth flounder (Atheresthes stomias), walleye pollock (Theragra chalcogramma), Pacific cod (Gadus macrocephalus), Pacific halibut (Hippoglossus stenolepis), and Pacific Ocean perch (Sebastes alutus). Average catch per unit of effort (CPUE) of all groundfish species combined increased with depth and had a significant peak near the shelf break at 150–200 m. Species richness and diversity had significant peaks at 200–300 m. The western GOA was characterized by higher CPUEs and lower species richness and diversity than the eastern GOA. Highest CPUEs were observed in Shelikof Strait, along the shelf break and upper slope south of Kodiak Island, and on the banks and in the gullies northeast of Kodiak Island. Significant differences in total CPUE among surveys suggest a 40% increase in total groundfish biomass between 1984 and 1996. A multivariate analysis of the CPUE of 72 groundfish taxa revealed strong gradients in species composition with depth and from east to west, and a weak but significant trend in species composition over time. The trend over time was associated with increases in the frequency of occurrence and CPUE of at least eight taxa, including skates (Rajidae), capelin (Mallotus villosus), three flatfish species, and Pacific Ocean perch, and decreases in frequency of occurrence and CPUE of several sculpin (Myoxocephalus spp.) species. Results are discussed in terms of spatial and temporal patterns in productivity and in the context of their ecological and management implications.

Distribution of decapod larvae in the Bombay Harbour-Thana-Bassein Creek regions

Variations in the abundance and composition of larval decapods were studied from 90 km stretch of the Bombay Harbour-Thana Creek-Bassein Creek (BHTCBC) system for a period of 15 months. The larvae belonged to Penacidea, Caridea, Anomura and Brachyura. Among these, brachyurans were the most abundant in the entire study area indicating good potential for crab fishery. Penaeus, Metapenaeus and Parapenaeopsis were the genera recorded in the family Penaeidae of which Metapenaeus spp. were the most common. Generally there was a higher abundance of Penaeus and Metapenaeus during monsoon probably indicating intense breeding. A few genera of decapods showed patchy occurrence in this system. Results of this first investigation were quantitatively and qualitatively evaluated with comments on fishery potential of the commercially important groups of decapods.

Water quality parameters of coastal shrimp farms from southwest and southeast regions of Bangladesh

The impacts of shrimp farming on water quality and effluent loading of shrimp farms in southwest (Khulna) and southeast (Cox's Bazar) regions of Bangladesh was investigated during March-August and August-October season, respectively. Water salinity fluctuated from 3.0 to 15.0 ppt in the southwest, whereas it was between 2.5 to 20.0 ppt. in southeast region. Total ammonia nitrogen as recorded in most farms of Cox's Bazar region was higher (0. 1160.438 mg/L) than the recommended level of shrimp farming. Mean values of total ammonia nitrogen and total nitrogen at the outlet of shrimp farms were higher than those of inlet in both regions. Mean values of phosphate phosphorus and total phosphorus at outlet were lower than inlet except in harvest time of Penaeus monodon. Total suspended solids were deposited on the bottom of shrimp farms in both regions, which resulted in higher concentration in inlets than outlets in both regions.

Some biochemical constituents and the calorific values of different regions of the body musculature of pond murrel Channa punctatus Bloch

A study of the distribution of some chemical constituents in the musculature of Channa punctatus Bloch showed it to be fairly heterogeneous. The increase in the levels of protein, fat, ash, total carbohydrates, glycogen, RNA, DNA and cholesterol towards the posterior region of the fillet was the result of increase in the number of cells per unit weight of the sample and in the concentration of myocommata. The distribution of water in the musculature was inversely related to that of the fat. The concentration of protein appeared to be associated with the RNA level. The posterior region of the fillet exhibited more calorific value than the anterior region.

Culture potential of Amblypharyngodon mola with carps in polyculture in farmers' pond of northern regions of Bangladesh

To assess the culture potential of mola (Amblypharyngodon mola) along with carps in polyculture systems, an experiment consisted of three treatments each with five replications was conducted for 4 months in two villages of Parbatipur upazilla under Dinajpur district. In the first treatment (SS), catla, rohu, mrigal, grass carp, Thai punti, common carp and a higher density of silver carp (8 per 40m²) were stocked. In the second treatment (SM), stocking density of silver carp was reduced to half and mola was added at a stocking density of 12,500/ha with all other fishes used in SS. In the third treatment (MM), no silver carp was stocked and mola was added at a stocking density of 25,000/ha with all other fishes used in SS. All treatments were subjected to the same regime of feed and fertilizers. The yields of large carps were 2035 kg/ha, 1757 kg/ha and 1326 kg/ha for treatments SS, SM and MM, respectively. Catla, grass carp and carpio showed better growth and production performance in presence of mola at a higher density, while rohu, Thai punti and mrigal showed better performance when stocking density of mola was relatively low. Mola yield was almost two times higher (184 kg/ha) in absence of silver carp (MM) than (62 kg/ha) in presence of silver carp (SM). The result showed that there was a significantly (p<0.01) lower total fish production in treatment MM. But there were no significant difference in total production between treatment SS and SM.