Ahyaudin B. Ali

Partial characterization and activities of proteases from the digestive tract of discus fish (Symphysodon aequifasciata)

A series of studies based on biochemical assays and electrophoretical observations was conducted in order to partially characterise various types of proteases present in the digestive tract of discus (Symphysodon aequifasciata), a highly valuable ornamental species. Casein digestion assays revealed the presence of acidic protease from the stomach region with optimum activity at pH 2.0 and alkaline proteases from the intestinal section with optimum activities observed at pH ranging from 7.5 to 9.0 and 11.5 to 12.5, respectively. Further assays with specific substrates and also pre-incubation with specific protease inhibitors showed the importance of trypsin and chymotrypsin in protein digestion while also revealing the presence of serine-proteases and metallo-proteases, respectively. SDS-PAGE technique using casein as substrate and specific protease inhibitors also showed the presence of eight distinct proteases based on molecular weights ranging from 19.2 to 76.5 kDa.

Effects of feeding rate on growth, feed utilizationand body composition of a tropical bagrid catfish

A 10 week experiment was conducted to determine theeffects of feeding rate on growth, feed utilizationand body composition of the tropical bagrid catfish,Mystus nemurus. Catfish fingerlings with anaverage initial body weight of 12 g were fed apractical diet (36.2% protein, 16.5 kJ/g diet) atrates of 1, 2, 2.5, 3, 3.5, 4 or 5% of their bodyweight (BW) per day in two equal meals. Watertemperature was approximately 29 °C throughoutthe experiment. Percent weight gain increased almostlinearly with increasing feeding rates up to 2.5%BW/day beyond which no significant (P > 0.05)improvement in weight gain was observed. The specificgrowth rate of catfish fed rations of 1% BW/day was0.72%/day and this increased significantly to anaverage of 1.39%/day for catfish fed 2.5% BW/day andbeyond. Feed utilization did not differ significantly(P > 0.05) between fish fed 1.0 to 2.5%BW/day but decreased when rations were increased to3.0% BW/day and above. Feed efficiency ratio was0.79 for catfish fed 1.0% BW/day compared to a ratioof 0.27 for fish fed at 5% BW/day. Catfish fed 1.0%BW/day had the lowest condition factor, hepato- andviscerosomatic indices, but the highest carcass tobody weight ratio. These fish also had lowerproportions of whole body dry matter, lipid andprotein, carcass dry matter and lipid, and visceraldry matter and lipid than fish in other groups. Therewere no significant differences in either conditionindices or relative body composition of fish fedrations of 2.0 to 5.0% BW/day. Based on the growth,feed efficiency and body composition data obtained, afeeding rate of 2.5% BW per day is recommended forM. nemurus fingerlings raised at 29 °C.

Distribution and habitat requirements of oxudercine gobies (Gobiidae: Oxudercinae) along the Straits of Malacca

Indonesian and Malaysian tidal flats along the Straits of Malacca were surveyed to determine the distributions of oxudercine gobies and their habitat conditions. Eight species from Penang Island and Selangor, Malaysia, and 12 species from Tebing Tinggi and Bengkalis Islands, Sumatra, were collected, including 2 species that had not been previously known to occur in these areas. Depending on the species, the habitats varied from sandy to muddy, level to sloped, exposed to immersed, wet to dry, and seashore to tidal river reaches.

A study on the epidermal structure of Periophthalmodon and Periophthalmus mudskippers with reference to their terrestrial adaptation

Epidermal structures of three species of Periophthalmus (Ps.) and two species of Periophthalmodon (Pn.) were investigated in relation to their lifestyle. All species of both genera lack a dermal bulge, which species of other two oxudercine genera, Boleophthalmus and Scartelaos, have in their epidermis. In Periophthalmus and Periophthalmodon species, which are highly terrestrial, the middle cells are well developed in the epidermis and the capillaries are distributed in the surface of the epidermis on the head and dorsal body. In Periophthalmus species and Pn. septemradiatus, the capillaries and blood vessels are also distributed in the epidermis of the abdomen, superficially in Ps. modestus and deeply in other species. In Ps. modestus, the capillaries are also densely distributed on the surface of the epidermis in the caudal area, whereas in other species, the epidermal capillaries and blood vessels of this area are located deep with a very low density. In Pn. schlosseri, the epidermal capillaries are not found in either the abdominal area or caudal area. A comparison of the distribution of epidermal capillaries among Boleophthalmus, Periophthalmodon, Periophthalmus, and Scartelaos species revealed that the skin makes a larger contribution to respiration in the species having a more terrestrial lifestyle. Goblet mucous cells are completely lacking in Periophthalmus species, whereas slimelike materials were often found on the skin surface of Periophthalmus species. This finding suggests that Periophthalmus species have some unknown mechanism for producing mucus. In Pn. schlosseri, exposure of the dense capillary net on the surface of the head is likely to increase cutaneous respiration, but it also makes the fish an attractive target of bloodsucking insects.

On the epidermal structure of boleophthalmus and scartelaos mudskippers with reference to their adaptation to terrestrial life

The skin structures of 4 species of oxudercine gobies (3 species ofBoleophthalmus and 1 species ofScartelaos) were investigated in relation to the terrestrial exposure of these fishes. These species have similarities in both lifestyle and skin structure. The specializations for terrestrial life mainly include the presence of dermal bulges, a thick middle cell layer, and a vascularized epidermis. Moreover, mucous cells are distributed only on the epidermis where the capillaries are undeveloped. In all species, the dermal bulges are large on the head and dorsal body, which are most often exposed to the air, and push up a thin epidermis, forming so-called papillae. Capillaries are densely distributed on the apical area of each papilla. InBoleophthalmus, the middle cell layer is thicker, the bulges are larger and distributed over a greater part of the body, and the area of the skin surface having the papillae is larger than it is inScartelaos. These differences suggest that the contribution of the skin to respiration is comparatively large inBoleophthalmus species, reflecting their more frequent activities on mudflats relative to the activities of theScartelaos species, which prefer to stay in the water. Mucous cells are abundantly distributed on the epidermis surface between the papillae in all species. The separation of the capillaries and the mucous cells may be due to an impeding of gas exchange by the mucus.

The reproductive biology of the cyprinid, Thynnichthys thynnoides (Bleeker), in the Chenderoh Reservoir — a small tropical reservoir in Malaysia

The reproductive biology and breeding cycle of a tropical cyprinid, Thynnichthys thynnoides (Bleeker), from Chenderoh Reservoir, Malaysia was studied from June 1991 to November 1992. A total of 329 and 246 mature females and males and 167 immature females were sampled during the study. Three breeding cycles were observed and the cycles coincided with high reservoir water level which resulted in the floodings of the littoral zone. Five and four gonad developmental stages were observed for females and males, respectively. Oocyte diameter distribution study indicated the species was a total spawner although clutches of ripe oocytes might be released over an extended time period. Fecundity was related to body weight and both absolute and relative fecundity increased with body size. Absolute fecundity ranged from 26962 ± 1484 to 173520 ± 127420 eggs fish−1, whereas relative fecundity ranged from 121 ± 53 to 451 ± 259 eggs g−1 body weight, respectively.

Effective use of plastic sheet as substrate in enhancing tropical oyster (Crassostrea iredalei Faustino) larvae settlement in the hatchery

Abstract Various methods were employed to exploit plastic sheet as substrate for enhancing tropical oyster ( Crassostrea iredalei ) larval settlement in the hatchery. Plastic texture (rough and smooth surfaces) and condition (with and without biofilm) showed a significant difference ( P P C. iredalei and Crassostrea belcheri promoted better setting rates (28.3±3.9% and 26.1±5.5%, respectively) as compared to those soaked in tissue extracts from other bivalve species such as the green mussel, Perna viridis (15.7±1.4%) and the rock oyster, Saccostrea cucullata (12.9±3.6%). The setting rate on the control was also low (15.3±2.7%) and was not significantly different ( P >0.05) from plastic with tissue extracts of the green mussel and the rock oyster. Exhalent water (used as media) from the above mentioned bivalve species were also found to increase oyster larval settlement on plastic substrate as compared to the control (without exhalent water). Higher setting rate was obtained for plastic with exhalent water from S. cucullata (48.9±3.5%) followed by C. belcheri (32.0±2.3%), P. viridis (30.4±4.3%) and C. iredalei (27.0±1.7%) which did not vary significantly ( P >0.05), while lower setting rate was recorded for the control (18.9±5.9%).

Aspects of the reproductive biology of female snakehead (Channa striata Bloch) obtained from irrigated rice agroecosystem, Malaysia

Snakeheads (Channa striata), collected for one year from February 1992 from the rice fields and the contiguous irrigation and drainage canals of North Kerian, Perak, Malaysia, were studied. There were six developmental stages of oocytes. Oocyte size frequency distribution and frequency of occurrence for the different ovarian stages indicated that gonadal development occurs throughout the year. Multi-modal oocyte size frequency distribution in the population indicated the presence of developing as well as mature oocytes in the females also confirms spawning readiness throughout the year. Estimates of mean absolute fecundity ranged from 4326 to 9017 oocytes whereas estimates of mean relative fecundity ranged from 10.5 to 36.3 oocytes per g body weight. Both TL (cm) and weight (g) can be used for estimating fecundity.

Seasonal dynamics of microcrustacean and rotifer communities in malaysian rice fields used for rice-fish farming

The abundance, seasonal dynamics and species composition of microcrustacean and rotifer communities in rice fields used for rice-cum-fish culture were examined. The shallow littoral-like nature of rice fields resulted in the presence of cladoceran and rotifer species, but copepods were numerically more abundant. Abundance and seasonal dynamics were affected by factors such as pesticides and herbicide use, predator-prey relationships, presence of hydrophytes and interactions among microcrustaceans and rotifers. The implications of microcrustacean and rotifers abundance and seasonal dynamics on rice-fish farming are discussed.

Some ecological aspects of fish populations in tropical ricefields

Fish yields from the captural method of rice-fish farming system were monitored from 1985 to 1987. Seven species were obtained, with Trichogaster pectoralis, Clarias macrocephalus, and Channa striatus dominant and economically important. Low number of species is due to double cropping of rice resulting in increased human activities. The maximum yield obtained, 174.6 kg ha−1, is probably near the maximum for this type of rice-fish farming and the harvests have also stabilised when compared to those obtained in the early 1970s. Fish populations included more than one year-class in each harvest. A decline in individual weight, especially of herbivores, was recorded and correlated to the abundance of the species, and hence, to food supply.