A global problem of today is the large amount of waste in the seas and oceans, primarily plastic waste. It is estimated that every year 1.25 to 2.41 million tons of plastic material is being carried by rivers into the seas and oceans. Waste is a major problem for marine organisms, causing entanglement, choking, strangulation, malnutrition and death. In 1972 the problems caused by microplastics, particles smaller than 5 mm, were first observed. Such particles bind pathogenic microorganisms on to their surface. Increasing quantities of microplastics have been found in the stomachs of fish, and also in shellfish that feed by filtering sea water. Ingested by marine organisms, such plastics may eventually pass through the food web and can end up ingested by humans. In addition, plastic releases chemical compounds whose effect on marine organisms and humans has still not been studied. Many international and state organizations offer solutions through recycling plastic waste, as well as reducing the production of plastic materials and informing the public about the problem.
Length-weight relations (LWR) and monthly occurrence are presented for juvenile fi sh, sampled from April to December 2018. in the of Donji Molunat bay, Croatia. From total number of 1448 caught fi sh of 30 fi sh species, 699 individuals of 16 fi sh species: Atherina hepsetus, Chromis chromis, Coris julis, Diplodus annularis, Gobius bucchichii, Microlipophrys canevae, Oblada melanura, Oedalechilus labeo, Pagellus acarne, Sarpa salpa, Serranus scriba, Siganus luridus, Symphodus cinereus, Symphodus doderleini, Symphodus ocellatus and Symphodus rostratus were analysed. Two parameters were measured: total length (TL) using precision ruler to the nearest 0.1 cm, and weight (W) using digital balance to the nearest 0.1 g. The b values ranged from 2.731 to 3.427, with median 3.0305. This study provides the fi rst LWRs for juvenile fi sh species in the Donji Molunat bay, as that it can serve as a tool used for future reference.
Rainbow trout Oncorhynchus mykiss (Walbaum 1792) larvae that first started active feeding were separated into 3 replicate batches (1A, 1B, 1C) with 100 individuals each, while four days later, the fry that last started active feeding were also distributed in 3 replicate batches (2A, 2B, 2C) with 100 individuals. Four measurements were performed with an interval of four days between the first and second measurements, as well as between the third and fourth measurements, to compare the initial masses of individuals by groups (1ABC and 2ABC) on the same day from the beginning of active feeding. The average initial body weight of the fry per batch in each measurement was generally higher in the first group (1ABC) than in the second group (2ABC). However, when comparing the weight of both groups for the same number of days from the beginning of active feeding, it is noticed that the second group (2ABC) has a higher average individual weight than the first group (1ABC). There was no statistically significant difference (one-way ANOVA, p>0.05) in SGRw between the groups in the first three measurements, while there is a statistically significant difference (one-way ANOVA, p<0.05) in SGRw in the fourth measurement. Group 2ABC has a significantly higher SGRw (5.0064%day−1±0.05394) than group 1ABC (4.7711%day−1±0.01715). This leads to the conclusion that in the second group 2ABC, the backlog of 4 days in mass was compensated. It is also noted that mortality in the first group (1ABC) was only 1%, while in the second group (2ABC) it was 3.7%. Consequently, a higher density of the fry in the first group (1ABC) could have an impact on a lower growth rate.
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