Otolith morphology analysis is one of the main tools used for fish or fish stock identification. Moreover, otolith shape can also be used in animal dietary studies (stomach content) for the identification of prey fishes and their size according to the relationship between fish and otolith sizes. In the present study, the relationship between fish length and otolith morphological dimensions was investigated for the sabre squirrelfish, Sargocentron spiniferum (Forsskål, 1775) (family: Holocentridae). Samples of 185 fish were collected from the coast of the Red Sea, Egypt. To analyze the relationship between fish and otolith, otolith morphometric measurements (length, width, area, perimeter, weight, sulcus, and ostium) and shape factors (aspect ratio, compactness, form factor, rectangularity, roundness, ellipticity, squareness) describing the outline shape were extracted using image analysis. Generalized linear models were applied for the relationship between body length and each otolith morphology feature. From the relationships between the total length of fish and fourteen morphology features, only otolith length, caudal length, and squareness were significantly correlated with fish size. Our results provide more information for the relationship between fish length and otolith morphometric features.

Macroalgae play a vital role in marine ecosystems, but human effects are threatening the composition and structure of algal communities. In the present investigation, the spatial and temporal variations of species composition, functional groups and percentage macroalgal cover were studied in relation to seasonal fluctuations of some physicochemical parameters, to determine the ecological status of macroalgae in coastal waters along the coast of the northwestern part of the Red Sea, from November 2020 to October 2021. Fifty-five species of macroalgae were collected and identified from the sites studied. Five functional groups of macroalgae were recognized. Among these were two turf-forming species, 34 species of upright fleshy algae, and three crustose algae. There was a large variation in the cover, as well as in the species richness and assemblage structure of the macroalgae in different sites and seasons. Seasonal changes, determined by environmental conditions, led to small changes in macroalgal cover at different sites, with the growth of some brown macroalgae suppressed by high sea temperatures, whereas some green and red macroalgae, increased in response to increasing temperature and salinity.

Rabbitfishes, family Siganidae, are one of the most abundant fishes inhabiting the Red Sea and now widely distributed in the Mediterranean. Age and growth of Siganus rivulatus, the most common species, were studied from samples collected randomly between October 2017 and October 2018 from Shalatein landing site. Otoliths of 2000 specimens were used for age determination and the maximum attained age for this species was four years. The von Bertalanffy growth parameters L∞, K and to and the instantaneous annual rates of total, natural and fishing mortality were estimated and consequently the exploitation rate was determined. It is found that the current exploitation level is higher than the optimum one reflecting the intensive exploitation of S. rivulatus in the Southern Red Sea, Egypt. Yield per recruit analysis revealed that fishing effort should be decreased. This can be adopted through closed seasons/areas, increase of mesh size, increase of minimum landing size and setting of a total allowable catch (TAC).

In this study, it has been recorded one species of family Latilidae (the Freckled tilefish Branchiostegus sawakinensis) in the coastal waters of the Egyptian Red Sea for the first time. It was found within the Nempiterus one sample that was caught by the line from Hurghada, Red Sea. It is the first documented record of this demersal species in the Red Sea, Egypt. This species is easily distinguished from Nempiterus samples by rectangular black blocks on the base of the dorsal membrane between fin rays and by prominent two horizontal yellow stripes observed on the caudal fin, and a noticeable dark spot on the operculum. Also, the morphometric and meristic characteristics were given together with some biological features.

The food and feeding habits of the two-bar seabream, Acanthopagrus bifasciatus fishes from Southern Red Sea, Egyptwere studied to know its feeding behavior in relation to sex, length and season as well as its preference for food items. Fish samples were collected monthly covering a period of 12 months from January 2015 to December 2015 and a total of 227 fish stomachs were examined for this study. The results indicated that Acanthopagrus bifasciatus fish feed on a variety of food materials mainly Mollusks (gastropods, bivalves and chitons), crustaceans (hermit crabs, crabs and eggs of hermit crab), fish scales, cnidarians (soft coral), Echinodermata as well as food remains. The variety of food substances in the stomach of Acanthopagrus bifasciatus shows that the species is a carnivorous. The feeding intensity showed its highest value during spring (76.74%) followed by winter (73.58%), while the lowest value was recorded during summer (57.14%). Acanthopagrus bifasciatus shifted their fullness index as they grow in length where the lowest value ofthis index was recorded for a length group 17–25 cm TL and the highest value was recorded for a length group 36–45 cm TL. The feeding habits of Acanthopagrus bifasciatus showed no significant difference between males and females and both sexes have the same diet composition with nearly the same concentration and distribution except for bivalves which were recorded only in the stomachs of female.