Comparative analysis of chemical composition of some commercially important fishes with an emphasis on various Malaysian diets

This study compares the chemical composition of cockle (Anadara granosa) and some commercially important marine (Asian seabass Lates calcarifer, grouper Epinephelus bleekeri, hardtail scad Megalaspis cordyla, longtail tuna Thunnus tonggol and Indian mackerel Rastrelliger kanagurta) and freshwater (sutchi catfish Pangasius hypophthalmus, Nile tilapia Oreochromis niloticus and eel Monopterus albus) fishes in Peninsular Malaysia. The results show that the proximate composition and trace metal content were significantly different (P < 0.05) among species investigated. The mean protein content was the highest in eel (19.1%) and the lowest in sutchi catfish (13.0%) and cockle (13.0%). The mean lipid content of Indian mackerel (3.9%) was higher than cockle (2.0%), followed by eel (1.3%) and longtail tuna (0.8%). The mean ash content was the highest in Indian mackerel (1.4%) and the lowest in cockle (0.9%). Zinc and manganese contents in cockle (Zn: 61.2 mg kg−1, Mn: 22.7 mg kg−1) were very high compared to other species investigated. The copper content was minimum in sutchi catfish (1.0 mg kg−1) and a maximum in the hardtail scad (11.7 mg kg−1). Trace metal content in sutchi catfish, Nile tilapia, grouper, longtail tuna, eel and cockle followed an order Zn > Mn > Cu, whereas Asian seabass, hardtail scad and Indian mackerel followed a different order Zn > Cu > Mn. Trace metal content in the tissue of the fishes examined was within safe limits for human consumption except Mn content in the cockle and Cu content in the hardtail scad, which is a matter of concern. When considering the daily fish fat, mineral and trace metal intake, marine fishes and shellfish are better than freshwater fishes.

Effect of Pre-Treatment on Physical Properties and Sensory Attributes of Gelatin Extracted from Sutchi Catfish (Pangasius sutchi) Skin

This study was conducted to evaluate the effect of pre-treatment on fishy flavor and odor removal of gelatin extracted from sutchi catfish (Pangasius sutchi) skin. Pre-treatment of the skin involved soaking at 4°C in distilled water (GC), lime followed by tamarind (GLT) or salt followed by activated carbon (GSC) prior to extraction in warm distilled water (50°C) for 12 hrs. Yield, physical properties and sensory were determined. Results showed that GLT produced highest yield (19.72%) compared to GSC (15.01%) and GC (15.81%). Although, GLT exhibited lowest gel strength (282.29g), viscoelasticity (14.1ºC) and setting point (10.46ºC) compared to other pre-treatments, fishy flavor and odor of the gelatin were almost absent obtaining the score of 1.68 and 1.74, respectively. These values were below those of reference which are 1.87 (fishy flavor) and 2.71 (fishy odor) denoting from ‘absent to weak’. Since fishy flavor and odor were almost absent, soaking sutchi catfish skin in lime followed by tamarind could be a good method to obtain gelatin with the desired sensory attributes.

MORPHOLOGICAL TYPES AND ARRANGEMENT OF CONE CELLS, AND THE VISUAL ACUITY OF SUTCHI CATFISH PANGASIANODON HYPOPHTHALMUS

The density and spatial arrangement of photoreceptor cells in the retina reflect the visual environment of a fish. The density of photoreceptor cells also determines the visual acuity. In this study, the morphological types and arrangement of cone cells, and the visual acuity of sutchi catfish Pangasianodon hypophthalmus were determined to obtain fundamental understanding of its vision. The left eyes of the adult sutchi catfish were enucleated, fixed in Bouin’s solution for 24 hours and then preserved in 70% ethanol. The fixed retinae were cut into 17 regions. The nine major regions were the dorso-nasal (DN), dorsal (D), dorso-temporal (DT), nasal (N), bottom (B), temporal (T), ventro-nasal (VN), ventral (V), and ventro-temporal (VT). The 17 regions were then immersed separately in a series of ethanol (from 70% to 100%), cleared with histolene, embedded in paraffin, cut into 6 μm thick tangential sections, and stained with haematoxylin-eosin. The density of cone cells per 0.01 mm2 in each region was counted from the stained sections. Visual acuity was then calculated using cone cell densities and lens radii. Only one type of cone cells, which is the single cone cell, was identified and these single cone cells were closely spaced. The area around the bottom region showed tendency of higher density of single cone cells. These findings provide the fundamental understanding on the adaptation of retinal structure of sutchi catfish to its feeding behaviour.